Login
"When tillage begins, other arts follow. The farmers therefore are the founders of human civilization."
- Daniel Webster
  You are here:  PublicationsPest ReportsPest Reports - 2013   
 MOFGA's 2013 Pest Reports - Compiled by Eric Sideman, PhD

September 13 | August 29 | August 2 | July 23 | July 11 | June 28 | June 12 | June 6 | May 29 | May 17 | May 7 | April 22
 
Show as multiple pages

Pest Report – September 13, 2013
Compiled by Eric Sideman, PhD, MOFGA's Organic Crop Specialist

COMMON GROUND FAIR – I will be at the Common Ground Fair next weekend, and all three days I will host a question and answer session about pests and other growing issues. Mark Hutton (vegetable specialist with the University of Maine) will join me. We have been doing it together for quite a few years now and it has become quite a lively time. We hope to see you there. It will happen Friday, Saturday and Sunday (September 20, 21 and 23) at 10:00 in the MOFGA Tent.

Harvesting sweet potatoes at Becky Sideman's research plots.
University of New Hampshire researcher Becky Sideman with a good harvest of sweet potatoes.
Covington sweet potatoes grown in New Hampshire.

SWEET POTATO HARVEST AND STORAGE

- Adapted by R. Hazzard from the New England Vegetable Management Guide, nevegetable.org; articles by Becky Sideman, UNH Cooperative Extension; wireworm information from J. Capinera Handbook of Vegetable Pests. Modified a bit by me.

Becky Sideman's fact sheet on Growing Sweet Potatoes can be found at

http://extension.unh.edu/resources/files/Resource000843_Rep881.pdf

Sweet potato acreage is steadily increasing in New England as it becomes clear that this crop can yield well, store well, and has a strong market. Sweet potato harvest and storage needs differ from other common New England root crops. Once harvest is completed – generally by early to mid-October – curing and storage issues continue to be important.

Sweet potato roots continue to grow until the leaves are killed by frost or until soil temperatures fall consistently below 65°F, whichever comes first. Time of harvest is often determined by digging up a few representative plants and determining the percentage of roots in different size classes. When tops of the plants turn black after the first frost, it is imperative to harvest as quickly as possible regardless of root size.

Sweet potatoes are very susceptible to damage at harvest. Sweet potato roots do not have a thick protective outer layer of cells such as that on white potato tubers. Abrasions and wounds can lead to rots in storage.

A freshly harvested sweet potato is more starchy than it is sweet. During curing and storage, starches in the sweet potato are converted to sugars, improving flavor. It is recommended to wait at least three weeks after harvest before consuming sweet potatoes (or selling without guidance to the customer to wait) to permit the starches to convert to sugars for maximum eating quality.

Curing immediately after harvest is recommended especially when sweet potatoes will be held in storage for retail or wholesale sales. Curing minimizes damage and loss during storage by healing harvest wounds. To cure, maintain roots in temperatures between 80°F to 86°F and a high relative humidity (85-95% RH) for 4 to 7 days. This forms a corky periderm layer below the damaged areas which limits microbial invasion and water loss. A greenhouse can provide good curing conditions, as long as the greenhouse does not get too cold at night. Sweet potatoes suffer when the temperature drops below 55 F.


Sweet potatoes can maintain excellent quality for up to a year in proper storage conditions. [Actually, Becky and I have eaten sweet potatoes nearly two years old and they seem fine.] The ideal storage conditions for sweet potato are the same as for winter squash; moderately warm (55-60F) at 60-75% relative humidity. Like winter squash, sweet potato suffers chilling injury at temperatures below 55 F. Signs of chilling injury include sunken, dark areas on the tuber surface, and blackening of tubers when cut open.

Yield studies were conducted for several years by Becky Sideman at University of New Hampshire. Best yields were found in Beauregard, Covington and O’Henry (a white-fleshed variety). A good yield was 2.5 lbs per plant, equivalent to >100 lbs per 20 row-feet.

Tuber damage from wireworms can occur during the growing season and reduce marketability. More work needs to be done to understand which species is causing the damage, but likely candidates are Corn wireworm (Malanotus communis) or wheat wireworm (Agriotis mancus). Both feed on roots, stems, stolons and tubers and are pests of potato, sweet potato, other non-root vegetables crops, and grains such as wheat and oat as well as sod and grassy cover crops such as Sudangrass. Adults are most active in spring (April-June). Eggs are laid in soil and larvae feed and develop for 2, 3 or 4 years. They can survive periods without food – essentially waiting for new crops to come along. Corn wireworm adults may be especially attracted to grassy cover crops such as Sudan, thus keeping fields free of those during peak egg laying is advisable. It is difficult to trace the history and cause of wireworm damage, because it often 2-4 years after eggs are laid before the damage becomes noticeable or serious. Damage is likely to be worst when larvae are nearly full grown. There are baiting methods to sample for larvae before planting. Corn wireworm larvae are also favored by wet soil conditions thus damage may be heavier in wet areas.

Voles love sweet potatoes and can take up residence in the sweet potato field, causing significant damage. Timely harvest may reduce the level of damage. Watch storage for vole activity after harvest.


Pest Report - August 29, 2013
Compiled by Eric Sideman, PhD, MOFGA's Organic Crop Specialist

We have moved past the problems associated with the very wet summer that many of us experienced. In fact, many growers are now complaining about the lack of rain. Now the typical late summer problems are popping up, and some new pest and disease problems are too. Although some very suspicious pictures came in today, there have been no other reports late blight in Maine or New Hampshire, other than the report from the mid coast a few weeks ago and regular reports up in the County. Lots of people have sent me pictures of leaf hopper damage (Pest Report June 6, 2013), or Botrytis on tomatoes (May 29, 2013 Pest Report), or early blight (June 12, 2013 Pest Report) thinking it is late blight. Please continue to send pictures of anything suspicious so I can clear your mind, or tell you to worry. Late blight symptoms include brown to black lesions on the leaves, with little or no yellowing. It usually spreads quickly. Often you also see brown lesions on the fruit. We are lucky up here in northern New England. There have been many reports further south and in New York.

In this issue:

Spotted Wing Drosophila Update
Basil Downy Mildew
Plectosporium on Summer Squash
When to Harvest Winter Squash

Wound in a blueberry, caused by Spotted Wing Drosophila (SWD). Berry softened by maggot of SWD. SWD maggot revealed.

SPOTTED WING DROSOPHILA (see the July 11 issue of the Pest Report for details)

Here on our farm the SWD is now in big numbers, as expected. Blueberries that we picked in July and most of August were mostly fine. Maybe we found a SWD infected fruit here or there. But now in late August it suddenly jumped to more than half of the fruit infected. The first sign is the fruit have a little hole or two in the side. That is where the fly laid an egg. I set some of those fruit aside on the counter and watched. The firm little berry with the hole got soft in about 3 days, and when cut open there was a maggot inside. If I had refrigerated it when I first picked it, the egg would have taken much longer to hatch and I could have eaten that fruit unaware.

Top

BASIL DOWNY MILDEW

Basil downy mildew
Basil downy mildew spore production

This is a pretty new problem, and it is all of a sudden widespread. We have lost all of our basil here on our farm, and the two farms I visited yesterday were quickly losing theirs. Downy mildew of basil was first reported in Uganda back in 1930. Recently it has been getting lots of attention as it spreads, first to Italy in 2004, France in 2005, United States (Florida) in 2007 and by 2009 New England. This year it is all over Maine and New Hampshire and we all have a chance to see it.

The first symptom is a pale yellowing of the upper surface of the leaves, quite similar to sunscald. Later, vein-bounded patches of dark spore production can be seen on the lower surface. This develops into a gray, fuzzy growth typical of downy mildews of other crops. At first you may be able to convince yourself that some soil has been splashed onto the underside of the leaf, but soon the plants will be going down and it will be clear that it is not a problem that can be washed away.

I bet that a lot more about this disease will be known next year than now. At this time we know that the disease may be seed borne, but that is probably a very rare event. The spread in most likely due to the wind blown spores. In the damp conditions of the early and mid summer they could move far and wide. There is also some belief that seedlings already infected and moved across country for sale play a role.

The infected leaves are safe to eat, and I have a report from a grower that mildly infected leaves still made a fine tasting pesto. Some types of basil are less or not susceptible at all. For example, my Thai basil is fine. I have heard from a grower that the lemon basil is not susceptible, and that the purple basil seems a bit less susceptible. The common sweet basil is the most susceptible. If you have this problem, and you grow more than one type of basil, please keep records and let me know if you see any resistance so we can make some recommendations for next year.

There are relatively few fungicides labeled for herbs. Also, I have not seen reports of efficacy of any. Some copper fungicides are labeled. Other OMRI listed products that are labeled for herbs include Actinovate AG, Trilogy, and OxiDate. But, again, I do not have any evidence that they are effective. If you try any of these, leave some plants untreated so we can get some information.

For now, anything that will make the leaves dry quickly will help, e.g., weed control, good spacing, venting tunnels, watering in the morning instead of the evening, etc.

Plectosporium blight on pumpkins
Plectosporium stem lesions
Plectosporium on zucchini fruit

Top

PLECTOSPORIUM BLIGHT [ON ZUCCHINI] (modified from a report by T. Jude Boucher, University of Connecticut, Cooperative Extension System)



Plectosporium blight, caused by the fungus Plectosporium tabacinum (formerly known as Microdochium tabacinum), is a relatively new destructive disease of cucurbits in New England. This disease was found in Tennessee in 1988 and has since spread rapidly throughout the eastern United States. It occurred on a single farm in Massachusetts in 2000 and on at least a dozen farms in Connecticut and Massachusetts in 2003. In the fall of 2004, after two seasons of rainy weather, it was present in every field Jude visited from Long Island Sound to Burlington, Vermont. I saw a lot of it in Maine in 2006, and I am now seeing it again this wet season, especially on zucchini.



Plectosporium blight is known to cause damage to a wide variety of cucurbit crops in Europe and Asia, but the strain present in the U.S. seems to primarily damage pumpkins, summer squash, zucchini and a few varieties of gourds. In wet years, which favor disease development and spread, crop losses in no-spray and low-spray fields can range from 50 to 100%.


This disease is easily recognized but is difficult for organic growers to manage. If you spot it, be prepared to implement good sanitation and develop an effective crop rotation of your cucurbits to clean fields next season.



Description and Management:

The clearest symptom to look for on vines and petioles are white lesions that tend to be diamond to lens-shaped; and on fruit and leaves the lesions are usually round and white.


Plectosporium blight is favored by cool, rainy weather. The fungus can overwinter on crop residue and thus can persist in the soil for several years. Plectosporium has not been reported to be seed-borne. Tiny, one or two-celled, sickle-shaped spores are formed in lesions on vines, stems, fruit, leaves and leaf petioles. Spores are dispersed by wind over long distances. Lesions are small (<1/4 inch) and white. The lesions increase in number and coalesce until most of the vines and leaf petioles turn white and the foliage dies. Severely infected pumpkin vines become brittle and will shatter if stepped on. Early in the infection cycle, foliage tends to collapse in a circular pattern before damage becomes more universal throughout the field. These circular patterns can be easily detected when viewing an infected field from a distance. Numerous fruit lesions produce a white russeting on the surface and stems that render the fruit unmarketable. Fruit lesions also allow for entry of soft rot pathogens that hasten the destruction of the crop.



Disease management recommendations include:



  • a 2-3 year crop rotation

  • planting in sites with good air circulation to encourage rapid drying of the foliage

  • switching to trickle irrigation if you have been using overhead

  • scouting fields to confirm the presence of Plectosporium, and plowing under crop residue after harvest

  • Although there are some fungicides for conventional growers, the fungicides available to organic growers are not thought to offer adequate control.

  • Winter squash curing in a greenhouse

Top

WINTER SQUASH LOOKS READY – SHOULD I HARVEST?

Winter squash look ready to harvest before they actually are mature. It is important to wait for maturity to have maximum storage and best eating quality. Most squash varieties reach full size by 20 days after fruit set. Accumulation of starch and other dry matter peaks at about 30-35 days after fruit set. But, the fruit is not fully mature until the seeds are fully developed, which occurs about 55 days for butternut. This is different for other varieties. If you would like to read more, take a look at this article by Brent Loy, the very well known plant breeder at the University of New Hampshire.

http://www.hort.cornell.edu/expo/proceedings/2011/Vine Crops/Maximizing Yield and Eating Quality in Winter Squash 11.pdf

Or, here is a summary put together by the folks at Johnny's Selected Seeds (see http://www.johnnyseeds.com/t-eating_quality_in_winter_squashes.aspx)

Harvest and Storage

Another critical factor in eating quality is maturity of the squash when it is harvested. Most small varieties reach full size by 20 days after fruit set. Accumulation of dry matter and starch content peaks at 30 to 35 days after pollination. However, the fruit is not mature until the seeds are fully developed, which occurs about 55 days after fruit set.

Dr. Loy stresses the importance of maintaining healthy plants until at least 50 days after fruit set because photosynthesis is essential to the development of sugars and dry matter. A squash that is picked too early will continue to develop seeds, but it does so by depleting the dry matter, thereby reducing eating quality.

Although fruit and seed maturity are similar across the three main species of edible winter squashes and pumpkins, harvest and storage recommendations vary by type.

Cucurbita maxima | Kabocha, Hubbard, and Buttercup Squashes

Kabocha, hubbard, and buttercup (C. maxima) varieties should be harvested before complete seed maturation, at about 40 to 45 days after fruit set, when the fruit is still bright green. That's when the rind is hardest, so less likely to be damaged in storage. They also are susceptible to sunburn as the vines die down, so it's best to get them harvested and out of direct sun before then to prevent the rind from turning brown or, with extreme sunburn, white. Kabocha squash have a high dry matter content and small seed cavity, so seed maturation off the vine is not a problem. However, once harvested, they should be stored at room temperature for 10 to 20 days to allow sugars to reach acceptable levels.

C. pepo | Acorn Squash, most Pie Pumpkins

Acorn squash (C. pepo) are misleading because they reach full size and develop a dark green-to-black mature color about two weeks after fruit set – 40 to 50 days before they should be harvested. Dr. Loy says that a better way to judge maturity is to look at the rind where it touches the ground. Immature squash have a light green or light yellow ground color, whereas mature squash have a dark orange ground color. Immature acorn squash have low sugar levels and although they will develop sweetness after harvest, they do so by depleting the dry starchy matter to convert it to sugars. This means storage life is shortened and eating quality declines.

C. moschata | Butternut Squash, some Pie Pumpkins

Butternut squash (C. moschata) are easier to judge by sight because they don't acquire their characteristic tan color until late in development, 35 days or more after fruit set. If the weather stays frost-free, they should be allowed to remain on the plants until 55 days after fruit set. In short-season areas, they often are harvested soon after turning tan because of the risk of frost damage. At that point, however, the sugars have not elevated to the 11% required for good flavor, so butternut squash harvested at 55 days after fruit set should be stored for 60 days at 56-60°F/10-16°C, with relative humidity between 50 and 70%. Carotenoid content also increases in storage, making the butternut squash more nutritious after it's been stored for a couple of months. To accelerate maturity and increase sweetness, Dr. Loy has found that butternuts held at warm temperatures (up to 85°F/29°C) for two weeks develop acceptable levels of sugars.

Top


Pest Report - August 2, 2013
Compiled by Eric Sideman, PhD, MOFGA's Organic Crop Specialist

This week offered much better weather for farmers. The summer bounty is beginning and many crops are looking good. On the other hand, as a pessimist I need to point out that some of the impact of the extreme weather (extremely hot or extremely wet) that filled most every day of the summer until this week are now showing up. I am seeing weather related problems such as blossom end rot in summer squash and tomatoes (wet or dry), stunted corn (loss of N), and dead buds in broccoli (heat). Late blight is being reported, but only pretty far away in places like PA, NY, OH and WV. There are no new reports in the Northeast. Squash bug eggs are hatching and if you are going to spray for this pest, the small nymph stage is the time to do it. Spotted wing Drosophila trap numbers are climbing fast. I have not heard about impacted fruit yet, and hope not to. Last year by mid August much of the soft skinned fruit was in sad shape. To lessen the impact, harvest frequently and thoroughly, and get the fruit refrigerated or frozen quickly. See the July 11, 2013 issue of the Pest Report for more details about SWD.

In this issue of the Pest Report there is information about a few problems out there or coming to a farm near you soon:

Buckeye Rot of tomato
Hornworms
Tarnished Plant Bug
Phytophthora Blight in cucurbits and peppers
Powdery Mildew in cucurbits

BUCKEYE ROT OF TOMATO

Buckeye rot of tomato
Buckeye rot of tomato. Tom Zitter photo.

I have had two reports of what I believe is buckeye rot of tomato. It is not a very common disease, but occurs sometimes in warm, wet conditions. We have had warm, wet conditions this year.

It looks a tiny bit like late blight, and in fact the pathogen is in the same genus as late blight (Phytophthora), but it is a different species. The first symptom is a brown spot, which enlarges and may engulf more than half of the fruit with a brown lesion that is made up of concentric rings of light and dark brown. Unlike late blight, the pathogen does not impact the foliage.

The pathogen survives in the soil and is spread by moving surface water or spattering rain or irrigation. Avoid poorly drained soil. Reduce compacted soil. Low areas in a field are particularly prone to the problem. Rotation with crops not in the tomato family will help reduce the pathogen level in the soil. Staking and mulching helps.

Top

TARNISHED PLANT BUG

Tarnished plant bug and leaf damage (lower left).

The tarnished plant bugs, and other plant bugs, are rampant again this year. It is a small (6 mm), bronze, brown and black bug that feeds on a very wide variety of plants. They overwinter as adults under debris and become active early in the spring. The population size explodes in fields of hay. When the hay is cut the critters fly in search of food and end up on fruit and vegetables. There are three or more generations per season. They are serious pests on strawberries (causing cat faced berries), lettuce (browning of midrib), Celery (causing scars on the petiole), flowers (destroying buds), eggplant and pepper (destroying buds so there is no fruit), broccoli (brown beads in the head), and much more. In potato they basically kill flowers (who cares?) and damage some of the leaflets (minor problem). But I often get calls about the browning leaflets from folks who think it is late blight.

It is pretty easy to kill them with pyrethrum, but not worth it because their numbers are so great in all the fields of hay and weeds surrounding you that what you kill will be replaced in a day or two. Weeding and nearby field management is about all you can do to keep the numbers low. I do cover all of my peppers and eggplants with a floating row cover and leave that on well into June.

Tomato hornworms.
Tomato hornworm frass below tomato plants.
Tomato hornworm hosting braconid wasp cocoons. Vern Grubinger photo.

Top

 

HORNWORMS

Hornworms are probably the most destructive insect attacking tomatoes and they are showing up now. They are giant caterpillars that can do a vast amount of eating in a very short time. Right now we are finding young, tiny ones. Sometimes it seems that overnight healthy looking tomato or pepper plants are stripped of their leaves leaving bare stems. The hornworms will also attack the fruit eating gouges out so large that they look more like bites of a furry animal than an insect.

Look now for the damage and the frass, which is black pellets laying all around plants hosting hornworms. The frass may be your first sign there is a problem. The frass of young hornworms is small. I don't bother looking for the caterpillar because they blend in so well, I just look for the frass.

The adults are large, fast flying hawk moths, which in flight may look like a hummingbird. At dusk they hover over flowers sucking nectar. Eggs are laid on tomato leaves and hatch in 5 days.

Hand picking is a bit frightening but does work and chickens enjoy fighting with the challenging pest. The problem with hand picking is that they blend in very well and it is easy to overlook one or two caterpillars, which can do significant damage in a day or two. I just got a report this year from a grower who is using a black light at night and finding the worm shining.

Bt works very well on this caterpillar.

 

WHAT ARE THOSE WHITE THINGS ON TOMATO HORNWORMS?

Tomato hornworm larvae are parasitized by a number of insects. One of the most common is a small braconid wasp, Cotesia congregatus. Larvae that hatch from wasp eggs laid on the hornworm feed on the inside of the hornworm until the wasp is ready to pupate. The cocoons appear as many small white projections protruding from the hornworm's body. Parasitized hornworms should be left in the field to conserve the beneficial parasitoids. The wasps will kill the hornworms when they emerge from the cocoons and will seek out other hornworms to parasitize. (Note: Picture is reprinted from a 2005 Vermont Veg and Berry News by Vern Grubinger.)

 

Top

 

POWDERY MILDEW 


Early symptoms of powdery mildew.
Powdery mildew on pumpkins.

Powdery mildew is a common disease of pumpkins and winter squash. All cucurbits are susceptible, but many common cucumber and melon varieties are resistant. The disease can cause infected leaves to die prematurely, reducing yields and lowering fruit quality, especially taste. Winter squash from diseased plants won’t store as long as fruits from healthy plants. The fungus that causes the disease does not overwinter in Maine. Spores blow up every year from southern overwintering sites. If they arrive late in the season, you may not need any control; but if they arrive in early to midsummer, exercise some control or you may have no leaves by mid-August, or bland starchy squash.

I am just seeing the first powdery mildew now. This may warrant attention. Go out and scout. Check upper and lower surfaces of leaves of older plants every few days starting now. The first symptoms usually are white, powdery fungal patches on the undersides of older leaves. Yellow spots may form opposite these, on the upper leaf surfaces.

No products with systemic activity (products that move through the plant) are approved for organic production, and applying fungicide to the lower leaf surface is difficult. In experiments, foliar applications of sulfur have been more effective than most other organic products for powdery mildew, apparently because sulfur deposited on the upper leaf surface can volatilize and be redistributed to the lower surface. Sulfur can be phytotoxic on melons, especially if applied when temperatures are hot.

There are some new products made from potassium bicarbonate (Kaligreen and Milstop are two of these) that are showing good efficacy. For a good discussion of these, including efficacy, see the new edition of the Resource Guide to Organic Insect and Disease Management at: http://web.pppmb.cals.cornell.edu/resourceguide/

ATTRA (National Sustainable Agriculture Information Service, (http://www.attra.ncat.org) reports that a single spray application (to runoff) of 0.5 percent (wt./vol. of water) baking soda, plus 0.5 percent (vol./vol. of water) SunSpray UFP® horticultural oil almost completely inhibited powdery mildew on heavily infected pumpkin foliage; while baking soda without the oil was ineffective, and a 2 percent (wt./vol. of water) solution of baking soda damaged the leaves.

Top

Phytophthora blight on pepper stem.

PHYTOPHTHORA BLIGHT ON PEPPER AND CUCURBITS

I recently received a few reports of phytophthora blight on pepper, and assume I will get some on cucurbits too. This is a disease caused by a pathogen in same genus as late blight (Phytophthora), but it is a different species. The problem only arises in wet areas in a field, which this year there are many of. Some years it is a very serious problem with pepper, eggplant, cucurbit and bean production. The plant will collapse as the pathogen attacks the roots and crown and girdles the stem. Fruit will rot where they touch the ground, or from spores carried by splashing water land on it. In cucurbits there is a white, yeast-like growth on the fruit.

The pathogen can be introduced on produce purchased from other farms, on shared equipment, and on irrigation or flood water. It lives in the soil and can persist many years. There are no materials that manage this disease and so control is based on cultural practices. A three year crop rotation to non host crops is recommended. All practices that prevent wet soil help (raised beds, choosing well drained fields, creating water ways, using drip instead of overhead irrigation, etc.).

Top


Pest Report – July 23, 2013
Compiled by Eric Sideman, PhD, MOFGA's Organic Crop Specialist

Leafhopper burn on potatoes Squash bug eggs
Leafhopper burn Squash bug eggs
Early blight Septoria leaf spot
Early blight on tomatoes Septoria leaf spot

As I write this it is raining again. Pouring you could say. Crops in soils with good drainage are doing well. Some soils have been waterlogged nearly every day of the season so far. Some crops have tolerated it well enough (sweet corn), and others have rotted away (ex. potatoes). Most crops are someplace between and have suffered a bit. The potato leafhopper is still active, and beans and potatoes left untreated in areas where they are plentiful are now showing hopperburn. Squash bug eggs are everywhere and soon the nymphs will be feeding. I recommend you be prepared for this (see the June 28, 2013 Pest Report). Late blight has only been reported in a few sites, and those pretty far away (MA, NJ, NY and one report in the County). Early blight and septoria leaf spot are running wild on tomatoes. It is a challenging year to farm or garden, and yet we have a wonderful bounty. I may sound like I am a pessimist but actually I recognize good fortune when I see it, and I see it now. Don't worry.

Covered in this issue:

Purple blotch in onions

Fusarium rot in garlic

Asiatic garden beetle

Imported cabbage worm

Purple blotch on onion leaves.


PURPLE BLOTCH ON ONION (Alternaria porri)

Purple blotch is a very common and sometime destructive disease that effects onions, garlic, shallots and leeks. Lesions begin as whitish sunken areas that elongate and develop purplish centers. Under favorable conditions (warm with wet leaves) the purple blotch lesions grow large and oval with concentric rings. The lesions may merge and take down whole leaves, and may become covered with brownish spores. The older leaves are more susceptible than the younger leaves.

Onion residue is the source of the disease in the spring. The fungal mycelium and conidia spores persist as long as the onion debris in the field or in cull piles. New conidia are produce on infected tissue in the spring and wind blown or carried in water to the new crop. The leaves have to have liquid water on them for the spores to germinate, but germination is very quick, less than an hour. Symptoms may appear in less than a week after germination and new conidia spores are quickly produced.

Cultural Control

Sanitation is very important to limiting spread. Infected crop debris should be destroyed or buried after harvest. Cull piles should not be kept near the new onion field. Onions should be grown in rotation with non host crops.

Materials Approved for Organic Production

Serenade has been shown to be effective against purple blotch.

Top

Fusarium rot on garlic. Lower photo by Crystal Stewart.

FUSARIUM ROT ON GARLIC (Fusarium oxysporum f. sp. cepae)

Now is the time to harvest garlic, or at least it will be shortly. And it is the time to check for problems. It is very important to determine if you have a problem with the garlic bloat nematode (see the June 28, 2013 Pest Report), or white rot (see the July 7, 2010 Pest Report. It may be a good time to pull out your copy of the Resource Guide to Organic Insect and Disease Management and read the Allium chapter* and become familiar with some other nasty garlic problems such as Botrytis rot and Penicillium decay.

Fusarium rot superficially looks like bloat nematode damage. The pathogen invades the basal plate and the roots decay and die. If the infection took place late in the season, then you may not see symptoms until the garlic is in storage.

Fusarium is a fungus that persists in soils as resting spores. Warm, moist soil favors development of the disease. Under very moist conditions a pinkish-white mycelium may develop making the symptoms a bit like white rot. If you are unsure whether your problem is the bloat nematode, white rot, or fusarium rot then you should send a sample into the Pest Management Office for identification (http://umaine.edu/ipm/ipddl/).

If you have a fusarium problem, then a three year rotation to crops other than any Allium is recommended. Garlic should be stored in a cool (320-360), dry place in order to slow the development of the disease. (see the MOFGA fact sheet Storing Garden Vegetables.


* The new edition of the Resource Guide can be ordered or viewed as a pdf at: http://web.pppmb.cals.cornell.edu/resourceguide/ or you can order a copy from MOFGA. Call the office (207-568-4142) or buy online at the  MOFGA Store. $20.00

Top

Asiatic Garden Beetle.

Asiatic Garden Beetle (Maladera castanea)

I have received a few reports of activity of this critter. The Asiatic Garden Beetle is a native of Japan and China where it is not an important pest. The pest overwinters in the soil as a grub feeding on the roots in sod ground and weedy gardens. Some farmers are reporting problem with the grubs in their crop fields. The larvae (grubs) pupate early in the spring and the resulting adults emerge in June and start feeding on all sorts of garden vegetables. The adults are cinnamon-to reddish brown, rounded beetles. They eat big and irregular holes in the leaves and blossoms. You have to look hard to find them because they feed at night and burrow into the soil for the day. If you see chewed leaves and no pest, then go out at night with a flashlight and see who is there. It will probably be cutworms, or the Asiatic garden beetle.

 If you have the problem, fall clean up with tilling the garden is important. Pesticides offer some control but often they are very numerous and seem to return from nowhere. Spinosad (Entrust and Montery Garden Spray) have been reported to work well.

For information about the other scarab beetles (including the Japanese beetle and oriental beetle) see the August 9, 2010 Pest Report.

Top

 

IMPORTED CABBAGE WORM (Pieris rapae)

The white butterflies are flying all around the cabbage family plants now and laying eggs, and the larvae (green caterpillars) are chewing holes in the leaves. If you have heading broccoli or cabbage you must know your customers because some folks are really turned off by the critters floating to the top of the water in the cooking pot. You may want to spray even though the crop is beyond risk.

This pest overwinters as a pupa and there are 3-4 generations per year. This means that once you start seeing the butterfly you should start scouting for the caterpillar in about a week. Bt (Dipel 2X or Dipel DF) or Entrust work very well in controlling the caterpillar. None of these materials lasts in the field and so should only be sprayed when the caterpillars are there in large enough numbers to warrant it.

Destroy or bury crop residue after harvest so as not to allow the caterpillars to continue to feed and complete their life history and thus a larger second generation later in the season.

Top


Pest Report - July 11, 2013
Compiled by Eric Sideman, PhD, MOFGA's Organic Crop Specialist

At this time the major concern in my mind is the number of leafhoppers I am seeing on beans, potatoes, and other crops too. Check the June 6 Pest Report for details on this pest, and scout your crops. Of course, the other major concern is wet weather, again. But I don't want to talk about it.

Pests and diseases coming up soon may be even worse. In this issue I will briefly cover the spotted wing drosophila and late blight. I will include links to more detailed reports.

Spotted wing drosophila

Late blight

Spotted wing drosophila on a tomato. Luckily, they only seem to go after cracked tomatoes.
Spotted wing drosophila larva in a raspberry.


SPOTTED WING DROSOPHILA

The spotted wing drosophila (SWD) has been found in Maine this week, and was found in southern New England a week or two ago. Only a few flies have been caught in traps set up to monitor the pest. It is in such low numbers that it is not a concern to fruit ripening now. But this pest has a proven record of explosive growth, and growers of soft fruits that ripen in August must be aware of the issue and make management decisions.

This fruit fly is a new pest in our region. It is a common pest in parts of Asia. The tiny fly looks like a typical fruit fly, but the males have a spot on each wing that you can barely see with the naked eye. Common fruit flies that we see here only go after over ripe and rotting fruit. The SWD is a much greater problem because it can attack sound fruit and has been very damaging to raspberries, blueberries and other late summer soft fruit. Two years ago was the first year it was seen in large numbers in northern New England. Last year on my farm in New Hampshire, nearly every raspberry and blackberry that ripened from mid August on had a maggot in it.

The fly lays eggs in the fruit and in a few days, perhaps on your customer's counter, maggots will be wriggling. In as few as 8 days it goes from eggs to new adults laying more eggs. The populations can explode quickly. And this is what has happened the past two years and is expected to happen again. A small population survives the winter, in early summer we start seeing a few flies around, by mid August fruit is being ruined, and by September nearly all soft fruit is being ruined. Some people escaped the damage last year.

Research is being done on various management practices for this new pest. At this time I do not have any fully tested recommendations. Here are some tips that have been learned in the past two seasons of dealing with this pest.

1) Trapping - Traps are very successful at monitoring the pest. The question that remains and is being researched this year is are traps useful for trapping out enough of the population to be an effective management technique. Here is a link to what has proven to be the best trap design:

www.uvm.edu/vtvegandberry/SWD/2013_SWD_Trapping.pdf

2) Netting to exclude the pest- Using nets such as Proteknet has proven successful. Whether this is practical is another question. Here is a link to a good source for commercial netting:

www.duboisag.com/en/proteknet-insect-netting.html

3) Cooling the fruit after harvest- After harvesting do not leave what looks like clean fruit on the counter at room temperature. You may be in for a surprise. Keep the fruit refrigerated until consumption, or freeze, and you may never know about any problem.

4) Pesticides are quite effective at killing this pest, but because of its quick generation time, and ability to migrate in quickly, spraying would have to be done more often then I could comfortably recommend. It turns out that spinosad (Entrust or Monterey Garden Spray) is among the best insecticide, even better than many conventional pesticides. However, not only is there reluctance to spray as often as would be necessary, there is a label restriction that crops may not be sprayed more than 3 times per season.

If you would like to read a lot more about this new pest, there are some very good fact sheets out there. I recommend the one from Penn. State:

extension.psu.edu/plants/vegetable-fruit/fact-sheets/spotted-wing-drosophila-1

Late blight on a potato leaf.

Top

LATE BLIGHT

The weather this year is as about as good as it gets for late blight. And, late blight has been found (in western Massachusetts, central New York and New Jersey and just this week in the County in Maine). It is still at a very low level and that speaks well to me of the efforts everyone is doing to manage it. For the most part, late blight only overwinters in New England in potato tubers and the low level of the disease this summer with this awful weather must be due to proper handling of diseased tubers, and the use of clean seed. Of course, no one brought in diseased seedlings to sell this year as they did in 2009, and that is a tremendous help.

On the other hand, with some late blight showing up here and there close to us, it is time to be vigilant. All of us need to be scouting our tomato and potato plants. If you find suspect plants, send me a picture or get a sample to your Extension educator.

For details about this pathogen and management of the disease, go to my article in The MOF&G:

www.mofga.org/Publications/MaineOrganicFarmerGardener/Spring2010/LateBlight/tabid/1555/Default.aspx

Top



Pest Report - June 28, 2013
Compiled by Eric Sideman, PhD, MOFGA's Organic Crop Specialist

It is wet again. Crops that were just beginning to recover are again turning yellow because of dying roots (no air) or loss of nitrogen (see the June 6th Pest Report for a discussion of how nitrogen is lost during wet conditions).

Pests that are quite common now include the three-lined potato beetle (June 6th Pest Report), Colorado potato beetle (May 29th Pest Report), Cutworms (May 7th Pest Report), cucumber beetle (May 29th Pest Report), and most worrisome is the potato leafhopper (June 6th Pest Report).

Squash bug adult and eggs.
Squash bug hatch.
Squash bug nymphs.

Problems that are now showing up and covered in this issue are the:

Squash bug

Squash Vine Borer

Garlic bulb nematode

Tortoise beetle

Buttoning of broccoli


SQUASH BUG

Squash bugs are now being seen in Massachusetts, southern New Hampshire and southern Maine. Squash bugs are serious pests throughout North America. When populations are high the entire crop can be destroyed. Damage and survival are low on watermelon, very low on cucumber and muskmelon, and highest on squash and pumpkin. Both adults and nymphs feed by inserting their mouth part and sucking juices from plant tissue. Toxic saliva injected during feeding causes foliage to wilt, then turn black and die. The severity of this damage is directly related to density of squash bugs on each plant. Often I get calls from growers who believe they have a disease. Later in the season, squash bugs may feed on the fruit, causing them to collapse or become unmarketable.
 
Adult squash bugs are a half to three quarters of an inch long, flattened and grayish-brown. They hibernate in crop debris in and around the garden for the winter and emerge in the early summer to feed a bit but mostly interested in mating and laying eggs. Eggs are laid in clusters usually on the underside of leaves and are orange when first laid, but turn bronze-colored before they hatch. The wingless nymphs are similar in appearance to adults. They are whitish when small, with a brown head, then turn gray when larger with black legs. There is one generation per year in the Northeast. The adults that arise from these nymphs will begin looking for a winter home in the fall.
 
Infestation is delayed by row covers. If possible, rotate cucurbit crops between fields as far apart as possible.
 
Black plastic, straw mulch, and reduced tillage systems encourage higher populations, probably by providing good hiding places. Remove plastic and straw mulch at the end of the season. Squash bug numbers are reduced by clean cultivation in the fall. Keep headlands mowed and free of trash to reduce overwintering sites.
 
Now is the time to scout undersides of leaves for squash bug adults and eggs. In small plantings you can reduce the population greatly if you crush the eggs you find. You may not want to crush the bugs as they stink when you do.
 
Squash bugs are unusually difficult to control with insecticides. Time squash bug sprays to kill young nymphs just after they hatch, because this stage is the easiest to control. I suggest that you mark some egg clusters when you find them with a piece of ribbon and then watch them over a few days to note when they hatch so you catch the nymphs when they are small. Squash bug adults and large nymphs are very difficult to control, especially when the canopy becomes dense. Treat very, very early in the morning or very late in the day when the flowers are closed to reduce risk to bees.
 
Pyrethrum and neem products have proved effective on the young nymphs. Some recent trials of mixtures of pyrethrum and neem have shown good control. There is a new material available called Azera, which is a mixture of pyrethrum and neem. Trials with this material for squash bug are happening this year at Cornell and I look forward to the results.

(Source material for this came from the New England Vegetable Management Guide, the UMass Vegetable Newsletter, and the Resource Guide to Organic Insect and Disease Management)

Squash vine borer.

Top

SQUASH VINE BORER

Squash vine borers (SVB) are showing up in traps in N.H., and I am sure that southern Maine is next. Many vine crops are beginning to bloom, and the row covers are being taken off to allow the bees access. That means the borer now has access too. Care should be taken during bloom to avoid using insecticides when the bees are active.

Squash vine borer moths are day-flying. They have a 1.0 to 1.5 inch wingspan and bright orange markings. In flight, they look like wasps. There is one generation each year. Adults emerge in late June/early July. The moths fly slowly in zig-zags around plants and lay eggs singly on stems; eggs are usually found on the main stem near the base, but are also found on leafstalks or on the undersides of leaves. Upon hatching, larvae bore into stems (where they are protected from insecticides). Thick-stemmed squashes are preferred. Unless you use traps or scout fields for evidence of eggs or larvae, the first sign of squash vine borer infestation is often wilting vines in July and August. By that time, it is too late to do anything.

Growers should scout their pumpkin and squash fields weekly for squash vine borer from late June through early August. Examine the base of vines for eggs. The squash vine borer can be killed with an insecticide and the recommendation would be spinosad (Entrust, Monterey Garden Spray), or the Bt aizaiwi strain (Agree WG). Appropriate timing is crucial. The insecticide is most effective when applied to young larvae before they bore into the stem. Once they are in the stem the insecticide will be useless. If you see the moths flying, or hear reports from local Extension about SVB flights, or find eggs, then two insecticide sprays, ideally applied to the base of the plants and timed five to seven days apart, will control newly hatching larvae before they are able to bore into the stem.

Again, the timing is crucial and there is no point in spraying before you find evidence, or after the larvae bore into the stem.

If evidence of larval feeding (sawdust-like frass near entrance holes) is found, then split open the stem to confirm the presence of larvae, which, by the way, may suggest more eggs are being laid so scout. Borers can be removed from vines if detected before much damage is done. Slit the stem longitudinally, remove the borer, then cover the wounded stem with moist soil above the point of injury to promote additional root formation.

Some growers monitor for the moths themselves using Scentry Heliothis pheromone traps from early June through early August. If more than 5 moths per week are captured, then they make 2 to 4 weekly applications of pesticides. Timing is very important, so this is not recommended for the casual gardener.

(Source material for this from the New England Vegetable Management Guide; UMass Vegetable Newsletter, The Resource Guide to Organic Insect and Disease Management, and the SVB Report from UNH Extension's George Hamilton)

Garlic bulb nematode.

Top

GARLIC BULB NEMATODE (Ditylenchus dipsaci)

The stem and bulb nematode, also called the garlic bloat nematode, is a new garlic pest in the Northeast, first appearing in New York in 2010 and now being found throughout the Northeast. It has been spread by infested garlic seed. I am already getting reports of growers finding it in their plantings this year. The microscopic worms feed by piercing root and leaf cells with their stylet. Leaves of severely infected plants turn yellow and dry prematurely. Plants may be stunted. The roots may be missing and the basal plate may appear to have a dry rot similar to Fusarium basal plate rot.

The pest is favored by wet, cool conditions. Although the pest is not active in hot dry weather, such weather may exacerbate symptoms. The nematode survives freezing and hot weather in soil and plant debris. It can only move short distances on its own. It is primarily moved by growers either moving soil (on tools, boots, etc.), in moving water, in debris from garlic or onion, or most commonly in garlic bulbs used for seed.


Most garlic naturally shows some yellowing of the tips of older leaves, so don't get worried right away. But, if you see some plants in your field that are significantly different than most with lots of yellowing, and they seem stunted, pull them up and check the roots. If a portion of the roots is missing, please get in touch with me and I will tell you where to send the sample for identification of this microscopic pest. DO NOT IGNORE THE PROBLEM, IT WILL GET WORSE. AND, MOST IMPORTANT, IF YOU SEE ANY, DO NOT SELL ANY GARLIC SEED. THIS COULD BECOME A MAJOR PROBLEM AND WE DO NOT WANT THAT.
 
Cultural Control

The best way to avoid garlic bulb nematode is to use your own garlic for seed, IF it is not yet infested. Monitor for symptoms of infestation during the growing season and submit suspect plants to a diagnostic lab for confirmation. Contact me to get instructions on how to take and where to send the sample.


If it is determined that you do have the problem, DO NOT use your own garlic for seed. Even bulbs that show no symptoms may have low levels of infestation. Obviously, do not sell any garlic for seed from a potentially infested lot. Do not replant garlic in an infested field for at least four years. Other hosts include all Alliums, celery, parsley, and salsify. Mustards, sorghum-sudan grass, and other bio-fumigant cover crops planted during the rotation period have been shown to reduce nematode populations in a field. These nematodes can survive in dry debris so carefully clean equipment and storage areas. 

There are no materials that offer control.

 

Top

TORTOISE BEETLE

This used to be a rare pest but this year I am getting many calls about them. Still, I do not believe that they do serious damage and do not warrant spraying. The numbers are usually very small and can be hand picked off. Of course, this could change. There is a tortoise beetle that feeds on sweet potatoes down south that is quite a serious pest.

They are oval to a square shape, clear to metallic looking with a dark square marking on the center of their back. Once you see one you will remember it. There are a few species of tortoise beetles. The one I am getting the most calls about is feeding on eggplants, tomatillos, peppers and potatoes. They overwinter as adults and come out in the mid spring. They eat holes in the leaves. When in small numbers, I recommend ignoring them or hand picking them off. If you have them in large numbers, please let me know.

Top

BUTTONING OF BROCCOLI

Every so often in some fields of early planted broccoli, there is a plant that prematurely forms a tiny, loose head. This is called “buttoning”. It usually happens when transplants go from growing quickly in the greenhouse to slowly because of some stress at transplanting. Flowering is triggered by this stress. This year, the cold period a few weeks ago may have both slowed growth and been an additional cue to flower through residual vernalization. Required vernalization by some species is a natural adaptation through which plant flowering is promoted by exposure to the prolonged cold of winter. This adaptation ensures that reproductive development and seed production occurs in spring and summer, rather than in autumn. Vernalization usually plays a minor role with broccoli, both because of its cooler growing season and because the vernalization response is fairly weak compared to other crops. Buttoning can also be caused by other stresses including hardening-off too quickly before transplanting, excessively wet or dry soil conditions, low soil nutrient levels, or high pressure from weeds, insects, or disease. Early season varieties are usually more susceptible to buttoning and bolting.

(Adapted from an article by Christy Hoepting, Vedge Edge Weekly: June 12, 2013, Cornell Vegetable Program)

Top



Pest Report - June 12, 2013
Compiled by Eric Sideman, PhD, MOFGA's Organic Crop Specialist

It is very wet, again. Crops are suffering from waterlogged soil and the loss of fertility, especially nitrogen, due to the excessive rains. In most fields, insects and diseases are much less of a problem than the excessive water and lack of sunny, warm weather. But that may change. Here are a few pests we are likely to see if it dries enough to walk in the fields.

In this report:

Striped Cucumber Beetle

Early Blight on tomato

Onion Thrips

Striped cucumber beetle

 

STRIPED CUCUMBER BEETLE

Striped cucumber beetle is our most serious early-season pest in vine crops. These beetles spend the winter in plant debris in field edges and with the onset of warm days and emergence of cucurbit crops they move rapidly into the field. Densities can be very high, especially in non-rotated fields or close to last year’s cucurbit crops. Adult feeding on cotyledons and young leaves can cause stand reduction, delayed plant growth, and reduced yield. The striped cucumber beetle also vectors Erwinia tracheiphila, the causal agent of bacterial wilt, and this can be more damaging than direct feeding injury. Crop rotation, transplants, and floating row cover are cultural controls that help reduce the impact of cucumber beetles. Many growers use row covers on cucurbits for both growth benefit and insect protection, and remove when flowering begins. Perimeter trap cropping with a preferred cucurbit crop (usually a C. maxima such as blue Hubbard or buttercup) can give excellent control with a dramatic reduction in pesticide use. For more details on perimeter trap cropping see articles on PTC at http://extension.umass.edu/vegetable/insects/cucumber-beetle-striped

Avoid early season infection with wilt. Cucurbit plants at the cotyledon and first 1-2 leaf stage are more susceptible to infection with bacterial wilt than older plants, and disease transmission is lower after about the 4-leaf stage. Using row covers at this most vulnerable stage can be very effective.

Thresholds and foliar controls. Beetle numbers should be kept low, especially before the 5-leaf stage. Scout frequently (at least twice per week before emergence, and for two weeks after crop emergence) and treat after beetles colonize the field. The threshold depends on the crop. To prevent bacterial wilt in highly susceptible crops such as cucumber, muskmelons, summer squash, and zucchini, we recommend that beetles should not be allowed to exceed one beetle for every 2 plants. Less wilt-susceptible crops (butternut, most pumpkins) will tolerate 1 or two beetles per plant without yield losses. Spray within 24 hours after the threshold is reached.

Insecticides that are allowed in organic production (listed by OMRI, the Organic Materials Review Institute, www.omri.org) include kaolin clay (Surround WP), pyrethrin (Pyganic Crop Spray 5.0 EC), and spinosad (Entrust). In 2009 UMass spray trials comparing these three products at the UMass Research Farm, kaolin was the most effective in reducing beetle numbers and feeding damage. There was a trend toward Surround WP being more effective when Pyganic or Entrust was mixed with it, but never significantly better than Surround alone. Surround should be applied before beetles arrive because it acts as a repellent and protectant, not a contact poison. With direct-seeded crops, apply as soon as seedlings emerge if beetles are active. Transplants can be sprayed or dipped before setting out in the field.

(Modified from the UMass. Vegetable Newsletter. Original written by Ruth Hazzard & Andrew Cavanagh)

Top

Early blight on tomato

EARLY BLIGHT ON TOMATO

Early blight is caused by two fungi that are serious problems in tomatoes and potatoes, but rarely affect peppers and eggplants. In most years, it is a much more common problem than late blight. All aboveground portions of the plant can be affected throughout the growing season. The disease starts on the lower leaves with small, circular spots that resemble a target with their concentric rings. Leaves develop yellow blighted areas, eventually turn all yellow and die. The tomato fruit may rot on the stem end. Though rare, potato tubers can also become infected. The pathogen overwinters on diseased plant residues in the soil. Initial infection is from splashing up from this overwintering site. By mid summer, most of the infection is coming from spores blowing in the wind from widespread infection in gardens and on farms across the region. It is important to avoid early onset of the disease because the longer you can avoid the problem the more likely it is that you will harvest red tomatoes before the plants die. Here are some cultural practices that can help avoid this disease.

Use crop rotations of at least three years to non-hosts (i.e., away from tomato, potato, and eggplant). Once the plant residue decays, the pathogen is gone.

Provide optimum growing conditions and fertility. Stressed plants (including drought or excessive moisture or shade) are more susceptible to early blight.

Stake or cage plants to keep fruit and foliage away from soil, and promote quicker drying.

Drip irrigation is preferred. If using overhead irrigation, start before dawn, so plants are dry early in the day. The key is to keep the period of leaf wetness to a minimum.

Mulching helps to prevent splashing of spores from soil up to lower leaves.

Indeterminate tomato and late-maturing potato varieties are usually more resistant or tolerant to early blight.

Early blight can be seed-borne, so buy from a reliable supplier. Hot water seed treatment at 122°F for 25 minutes is recommended to control early blight on tomato seed.

Each season, disinfect stakes or cages with an approved product before use. Sodium hypochlorite at 0.5% is effective and must be followed by rinsing and proper disposal of solution. Hydrogen peroxide is also permitted.

Grow tomatoes in a high tunnel or caterpillar tunnel. Tomatoes grown with such protection rarely suffer from early blight because there is less splashing and wind blown spores and the leaves are drier.

Top

Onion thrips damage

ONION THRIPS

Onion thrips may become active soon, and if they have been a problem for you in years past it is time to start scouting for them. They are very tiny and easily overlooked until the onion plants start showing leaves that look as if they have been rasped. In fact they have. The thrips feed by using their moth parts to rasp and pierce the onion leaves, releasing juices for them to feed upon. If the population of thrips is large you will see silvery patches on all the young leaves and when really bad the whole field will look white and silvery and the leaves wither. Obviously onion yields can be greatly reduced because the onion plants loses food and water through the damaged tissue. It is best to get control of them now before the populations grow.

Onion thrips hide between the leaves at the base of the onion plant. I find the best way to find them is to pull up a plant and hold it upside down over a white sheet of paper and pull apart the leaves as you shake gently. Even when they are walking about on the paper you will still need to look hard to see the thrips. My eyes are not that good and I need a hand lens to even spot them. The immature thrips are white to a pale yellow, elongated with very short antennas and dark eyes. Remember, tiny. The adult is tiny too, but it has wings. Thrips' wings are unique. They are fringed with hairs. Thrips are very poor fliers, but they do fly when disturbed, and they do get blown in the wind easily. Keep in mind that this means thrips will be blown to new fields downwind. Adults are pale yellow to dark brown.

There are many generations per season and they can be very quick in warm weather. Also, parthenogenesis is common, meaning females that cannot find males produce progeny all by themselves. Each female can produce up to 80 eggs, which tells you that the population can explode quite quickly under good conditions. Good conditions are warm and without heavy rains. Heavy rains wash the weak insect off the plant.

Growers can simulate heavy rains with heavy overhead irrigation. As well as disturbing the insect the extra water will help the rasped onions. Extra fertilization will help too.

Thrips survive in onion and garlic debris so clean up after harvest. I have heard that thrips are confused by inter-cropping with carrots.

If the natural enemies or the cultural practices fail to keep thrips populations down then you may need to turn to a pesticide. Remember, thrips are often around in small numbers which can be tolerated. IPM practices recommend an economic threshold of an average of 3 thrips per green leaf. When scouting, sample about 50 plants around the field from at least 10 different locations in the field and then figure the average per leaf. Entrust is the most common recommended material. Follow the label instructions and be sure to spray into the leaf axis. Surround is reported to deter thrips, and may be the better choice if you have had bad thrips problems in the past.

See the most recent issue of The Maine Organic Farmer & Gardener for an excellent article about thrips by Tom Vigue. www.mofga.org/Publications/MaineOrganicFarmerGardener/Summer2013/OnionThrips/tabid/2616/Default.aspx

Top



Pest Report - June 6, 2013
Compiled by Eric Sideman, PhD, MOFGA's Organic Crop Specialist


In this report:

Potato Leafhopper

Three-lined potato bug

Wet weather again and nitrogen

Leafhopper burn
Leafhopper nymph (circled)


POTATO LEAFHOPPERS

Potato Leafhoppers (PLH) have made it to Maine. This is the earliest I have ever seen them here. They are in big numbers in some fields, which may be very bad news. They are likely to be moving north so be on the lookout. They primarily feed on beans, potatoes, eggplants, strawberries and alfalfa.

PLH does not over winter anywhere near here. They overwinter way down south on the coast of the Gulf of Mexico, and leapfrog up here in mass migrations. Once they get here there are a few generations during the season and often become a bigger and bigger problem. The first to arrive are females, and they are usually carrying fertilized eggs when they get here. They first land in trees. They were spotted last week in apple trees in Massachusetts. This week I got two calls about them from MOFGA certified farmers in southern Maine, and so I went out to check my potatoes. Yup, there too.

The damage from leafhopper is catastrophic. The bug sucks the juice out of the plant and injects a toxin that clogs the food conducting tissue. The symptoms look like a disease after a while, rather than insect damage, and is frequently mistaken as such. The leaves first get pale, then yellow and then brown from the edges. Then the plant dies. The symptoms are called hopperburn.

The adult PLH is very light green and wedge shaped and tiny (an eighth of an inch long). The best way to find them is to brush the plant, see a bunch of these tiny things fly up, and watch one of the white-looking bugs land. The nymphs are similar to the adult, but have no wings and are even smaller. Nymphs live on the underside of the leaves. If you disturb a nymph you will see it run and it can run sideways as fast as forward. This is a clue that you have PLH and not some other less harmful species of leafhopper.

The adults are flighty. When you brush your crop you will see them fly up. If there is a cloud of them, you are in trouble. Researchers have developed a threshold before treatment is recommended. Thresholds vary but here is one that is typical: Treat potatoes if 5 adults or 15 large nymphs are found on 50 leaves.

Crop rotation does nothing for you since they are coming from far away. Covering your crops with a row cover would work, but these crops are not the type that are usually covered. Effective insecticides are limited. The only material that I have seen work that is allowed in organic production is pyrethrum, so Pyganic is the recommendation that I make. However, it does not work as well as a pyrethrum with PBO, BUT PBO is not permitted in organic production. If you market crops as organic, be sure to use an approved brand. Use the most concentrated mix allowed. Spray late in the day or evening, get good coverage including the undersides of the leaves, and don't wait until it is too late. If you wait to see damage, it is too late. Plants will not recover.

Top

 


CUCUMBER BEETLES ON MY POTATOES and TOMATILLO?

No. Those are not cucumber beetles. Potatoes, tomatoes, tomatillos, and sometimes eggplants are attacked by this pest that only superficially looks like a cucumber beetle. This is the THREE-LINED POTATO BEETLE. The adult of this pest is about the same size as a cucumber beetle but has a reddish head and a thorax with two dark spots. The wing covers are dark yellow with three black stripes. Its favorite food in my experience is tomatillo.

The Three-Lined Potato Beetle overwinters as an adult and wakes early in the spring. They are there waiting for you to plant your solanaceous crops. The females soon begin laying eggs that hatch in about two weeks to larvae that look a bit like Colorado potato beetle larvae, except these critters have the endearing practice of carrying a small pile of their own excrement on their back. The larvae mature in about two weeks. There are probably two generations per year.

On most crops the level of the pest does not warrant control. If this pest has been a problem in the past, floating row covers will help you avoid the overwintering adults and that should get you by. Hand picking will work on small plantings. Pyganic and Entrust may offer some relief. Rotenone works well, BUT REMEMBER THAT THERE ARE NO ROTENONE FORMULATIONS THAT MEET ORGANIC STANDARDS.

Top


WET WEATHER AGAIN and NITROGEN

Crops suffer from wet weather and I am getting calls about yellow/purple, dwarfed corn, broccoli, spinach, etc. Crops suffer for two main reasons. The first is that the roots of nearly all crops need air that they can only get from the spaces in the soil. If those spaces fill up with water there is no air. There is not much you can do about that.

The second reason is nitrogen. Nitrogen is an integral part of the protein molecule and all living things need it. Plants get their nitrogen from the soil and pick it up as dissolved ions, either the nitrate ion or the ammonium ion. Organic farmers and gardeners typically put down nitrogen fertilizer as protein in forms such as soy meal, fish meal, blood meal, livestock manure, etc. A bit of the nitrogen in manures is in the ionic form already, and if you use something like Chilean nitrate, it is all in the ionic form. To get a detailed discussion of these different forms of nitrogen, how they cycle around from one form to another, and how plants pick it up, see the MOFGA Fact Sheet called Providing Nitrogen to Crops at http://mofga.org/Portals/2/Fact Sheets/FS 08 Nitrogen web.pdf.

The important point to make is that lots of rain means loss of nitrogen. Even if you put down fertilizer, it is likely to be lost to a greater or lesser degree by lots of rain. And, lots of rain is in the forecast again. If your nitrogen is in the protein form, it is likely to be OK, but if it is in an ionic form, it is soluble and is likely to be lost. Or if your soil becomes water logged, your nitrogen fertilizer may be lost to the air as a gas. Pay attention, think about how long ago you added the fertilizer and if it has decomposed into the ionic form yet, or not. You may have to side dress your crops with more nitrogen.

Top


Pest Report - May 29, 2013
Compiled by Eric Sideman, PhD, MOFGA's Organic Crop Specialist

In this report:

Cucumber problems (when planted early)

Colorado potato beetle

Gray mold

Mexican bean beetle


CUCUMBER PROBLEMS

Blame it on global warming, or not, we have experienced extremes that average out to pretty normal, but we don't often see a normal day. After about three weeks of very dry weather, we just went through a week of very wet weather. Now most fields are wet, some are water logged. This is not good for roots.

The roots of plants need oxygen and most plants are not able to move oxygen down to them. Roots get oxygen from the spaces between the soil particles, and if these spaces are filled with water there is none there. Roots without oxygen do not function well and the plant is stressed. This week I have seen plants stressed to the point of wilting, some only to the point that they are weak and diseases win out.

Cucumbers have been the hardest hit. Many growers who are rushing things and have put their cucumber seedlings out are reporting problems. Some years you get away with rushing things, some years you don't. I have seen chilling injury (Chilling injury is damage to plant parts caused by cool temperatures but above the freezing point. Plants of tropical or subtropical origin are most susceptible. Temperatures below 50 degrees F. will set back cucumbers). I have also seen damping off. And, I have seen seedcorn maggots crowded into the stems of cucumber plants. Read the May 7 and April 22 pest reports for a discussion of these early season problems (see menu tabs at the top of this page).

Top

COLORADO POTATO BEETLE

Colorado potato beetle eggs
Colorado potato beetle at the 4th instar
Adult Colorado potato beetles

Colorado potato beetles (CPB) adults are not yet showing up in potato and eggplant crops, but will soon. The bright yellow eggs are laid in clumps with about 30-35 eggs each, generally on the undersides of leaves. As with most other insects and plants, there is a direct relationship between higher temperatures (in the range between about 55 and 90 degrees F) and faster rate of development. That includes egg-laying, egg hatch, larval growth, and feeding rates. A period of cold, rainy weather slows everything down, but we can expect a surge of adults and shiny yellow eggs to appear after a few hot spells.

Scouting and Thresholds

Walk your fields and look for CPB adults and eggs. A treatment should be considered for adults when you find 25 beetles per 50 plants and defoliation has reached the 10% level. The spray threshold for small larvae is 4 per plant; for large larvae, 1.5 per plant (or per stalk in midseason).

Eggplants are more sensitive. Controls are needed on eggplants when there are 2 small or 1 large larvae per plant.

Potatoes can tolerate 20% defoliation without reduction in yield (or even more, depending on time of the season and cultivar). Damage to eggplant seedlings from adult feeding is often severe enough to warrant control of the adults, but in potato, damage from adults may not be significant, so you may be able to wait until after egg hatch to kill both adults and larvae.

Look on the undersides of leaves for the orange-yellow egg masses. The fresher the eggs, the brighter orange the eggs will appear. Eggs hatch in 7-10 days, depending on temperature. If you want to know when the earliest eggs are hatching, you can flag a few of the earliest egg masses you find with bright tape or flags, and then keep an eye on the hatch.

Hatched larvae go through four stages (called instar) before they become adults. In the first stage, the larvae are about the same size as the eggs, and in the second stage they are about an eighth of an inch long. As the larvae get bigger, they do more feeding. The fourth, or largest, stage does 85% of the feeding damage. It’s a good idea to prevent beetles from ever reaching the fourth instar!

After larvae complete their growth, they drop to the ground and burrow into the ground to pupate. About ten days later the next generation of adults emerges – ready to feed. If they emerge before August 1, they will lay more eggs. After August 1, they feed and head to overwintering sites. Good control in June prevents problems with CPB in August.

Cultural Controls

Crop Rotation. The single most important tactic for CPB management is to rotate potatoes or eggplant to a field that is at least 200 yards from the previous year’s fields. Since the adult that comes out of winter cannot fly, barriers such as roads, rivers, woodlands, and fields with other crops are helpful. Rotated fields tend to be colonized 1-4 weeks later in the season. Also, the total population of adult beetles is lower, producing fewer larvae to control.

Perimeter treatments or perimeter trap cropping can be applied to potato. One approach is to plant a barrier crop between overwintering sites and this year’s crop and get it in earlier than the main crop; then control early-arriving beetles.

Early planting. Green sprouting, also know as chitting, prepares whole seed potatoes to emerge rapidly, gaining about 7-10 days to harvest. This early start makes it easier for the crop to put on growth and size before CPB adults and larvae arrive. It can be combined with raised beds and plasticulture. While it won’t avoid damage altogether, it may reduce the need for insecticides. Refer to the New England Vegetable Management Guide (www.nevegetable.org) for more details.

Late planting. Another strategy for beating the beetle is to plant late. CPB adults that do not find food leave the field in search of greener pastures. Planting after mid- June, using a short season variety, often avoids CPB damage and eliminates the need for controls.

Straw mulch. It has been well documented that when potato or eggplants are mulched with straw, fewer Colorado potato beetle adults will settle on the plants and fewer eggs will be laid. This can be accomplished on larger plantings by strip planting in a rye mulch, followed by mowing and pushing the rye straw over the plants after they emerge. For smaller plots, straw may be carried in.

Biological Control. There are numerous predators and parasitoids that attack CPB adults (a tachinid fly) and larvae (12-spotted ladybeetle, spined soldier bug, ground beetles).

Organic pesticides. Spinosad (Entrust) and azadiractin (AZA-Direct) are two options. Recent studies have shown very good results with spinosad, but please use reluctantly because resistance will build up in populations of CPB. The azadiractin has shown some efficacy, but neem works slowly. Generally it is used to reduce overall damage and reduce numbers but it is not a rescue treatment like spinosad is. Beauvaria bassiana (Mycotrol O) has been shown to suppress CPB populations though does not provide immediate control. And, using Beauvaria bassiana does not jive well with using crop rotation because you need the overwintered adult that remain infected with the fungus to eliminate buying the product new every year. But, if you are in a situation where rotation is not possible anyway, Beauvaria may help manage this pest.

[NOTE: There is no longer a registered Bt product for potato beetle management in organic crops.]

(Modified from the Umass Vegetable Notes, an article by R. Hazzard; (sources include: D. Ferro (UMass Amherst), J. Mishanec (NYS), J. Boucher (CT), J. Whalen (DE), T. Kuhar (VA), , G. Ghidhu (NJ), New England Vegetable Management Guide, Ohio Vegetable Production Guide)

Top

 

GRAY MOLD (Botrytis cinerea)

Botrytis (gray mold) on strawberries
Gray mold on peas
Botrytis sporulating on a tomato leaf

Gray mold is a fungus that you cannot run and hide from. The spores are blowing everywhere. It is a very common problem on soft fruits (ex. strawberries) and all sorts of vegetables. We organic growers must be aware of the conditions that favor the fungus over our crops and do our best to manage them. Botrytis is favored by cool, rainy, foggy and generally moist situations. It is time to worry, especially for strawberries because the initial infection is usually on senescent tissue, for example the old petals and sepals senescing right now. This is true for tomatoes (high tunnel), peas, and other vegetables too where flowers are now senescing. Wounded stems or leaves are also points of infection. The disease then spreads from there if the conditions are right to favor the fungus over the crop.

Even though you may not spot the problem until you are harvesting strawberries and you see the typical gray fuzzy mass of fungi and spores, the initial infection took place during bloom. And, during bloom this year it is wet.

Botrytis is often a problem in weedy fields, or where the foliage is too dense, e.g., the lower leaves of a lush row of tomatoes (especially in a high tunnel) or lower leaves in the dense growth of potatoes. Essentially, where the plant tissue stays damp and cool for a while there is a risk of Botrytis, especially if there is senescent tissue. I often get many people calling with fear they have late blight when really they have Botrytis gray mold. If you get the typical gray fuzzy growth it is easy to tell. Gray mold will form lesions on leaflets of potatoes or tomatoes and progressively expand to include the whole leaf and then the petiole and stem. Lesions on lower parts of the stem may girdle it and the plant will wilt. A key distinction from late blight is the gray mold lesion is usually associated with yellowing of the leaf (see picture).

After the rainy weather most of us are experiencing this spring, I suggest you pay close attention to anything that would lead to damp conditions. What I think is really important now is to get the weeds under control, do not allow foliage to get too dense, and use wide spacing between rows of crops.

Top

 

 

MEXICAN BEAN BEETLE

Plan Ahead for Biological Control
(Reprinted and modified from Mass. Veg. Notes, written by Ruth Hazzard and A. Brown)

Mexican bean beetle larva
Adult Mexican bean beetles

If Mexican bean beetles have historically been a problem on your farm, you will very likely see them again this year. They may be pests on snap beans, soybeans, and lima beans. While they are not a pest on every farm, some farms report repeated significant damage from these pests and have to take action to prevent crop loss. Using biological control can reduce the need for insecticides.

Mexican bean beetle (MBB) adults are coppery brown with black spots. They look very much like large ladybeetles and in fact are closely related – but unlike lady beetles they feed on leaves, not other insects. Adults lay yellow-orange egg masses on the underside of bean leaves. These hatch into bright yellow, spiny oval larvae, which feed, molt several times as they grow, and pupate on the underside of leaves. Feeding damage from adults and larvae can reduce yield and injure pods if numbers are high. There are several generations per season, often with increasing populations in each generation.

Pediobius foveolatus is a commercially available biological control agent for Mexican bean beetle control and has a good track record in the mid-Atlantic states and among New England growers who have tried it. (Pediobius is pronounced “pee-dee-OH-bee-us”). It is mass-reared and sold by the New Jersey Dept of Agriculture and is also available from other beneficial insect suppliers. This small (1-3 mm), non-stinging parasitic wasp lays its eggs in Mexican bean beetle larvae. Wasp larvae feed inside the MBB larva, kill it, and pupate inside it, forming a brownish case or ‘mummy’. About twenty five adult wasps emerge from one mummy. Control continues and in fact gets better as the season progresses and successive generations of the wasp emerge and search out new bean beetle larvae. Planning 2-3 releases at 7-10 day intervals will help ensure good timing. and coverage on several plantings. This makes it well suited to our succession-planted snap bean crops. After a release in the first plants, it is advisable to leave that planting intact for a while, until the new generation of wasps has emerged from their mummies. As with any biological control, make releases as soon as the pest is present – not after it has built up to damaging numbers.

The New Jersey Dept of Agriculture Beneficial Insect Rearing Laboratory recommends two releases, two weeks in a row, coinciding with the beginning of Mexican bean beetle egg hatch. Wasps will lay their eggs in larvae of any size, but it is best to target the newly-hatched young MBB larvae. This will give control before damage has been done. Thus, timing is important. Watch for eggs and time the shipment for the first hatch of eggs into larvae. If in doubt about the timing of the hatch, release as soon as you see the eggs – if you wait for the larvae you may be playing catch-up. The release rate should be at least 2000 adult wasps per field for less than an acre, or 3,000 per acre for fields of one acre or more.

The 2009 cost from NJDA is $40 plus shipping for 1000 adults, or $20 for 20 mummies (pupal parasites inside dead MBB larvae) from which about 500 adults will emerge. Order adults if you already have MBB larvae in the field. Ship for overnight delivery. Instructions for handling and release will come with the wasps. Wasps reproduce in the field and will still be around when the second generation of MBB hatches out. Thus, it should not be necessary to make more than two releases. Like beans, Pediobius wasps are killed by frost.

Plan ahead by contacting a supplier to inform them of your expected release dates and acreage.

Contact information for New Jersey source:
Tom Dorsey, 609-530-4192;
NJDA, Phillip Alampi Insect Lab, State Police Drive, W. Trenton, NJ 08628.
http://nj.gov/agriculture/divisions/pi/prog/beneficialinsect.html.

You’ll also get advice on how to use the wasps from this office.

Pediobius is also available from the following suppliers:

Green Spot Ltd. (N.H.)
www.greenmethods.com
603-942-8925;

IPM Laboratories (N.Y.)
www.ipmlabs.com/
315-497-2063;

ARBICO (Ariz.)
800-827-2847
www.arbico.com/

Network (Tenn.)
615-370-4301
www.biconet.com/.

If you would like assistance in using these biocontrols in your bean crops please call the UMass Extension Vegetable Program at 413-577-3976 or 413-545-3696 or email at umassvegetable@umext.umass.edu

Materials Approved for Organic Production

Moderate control can be achieved with Entrust as well as mixtures of pyrethrin (Pyganic EC5.0) and Neemix.

Top


Pest Report - May 17, 2013
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist


In this report:

Potato seed issues

Flea beetles

Oedema on tomato and related crops

Late Blight symptoms on tuber. Photo by Steve Johnson, University of Maine.
Fusarium rot on potato seed pieces
Ring rot on potato tuber
Black scurf on potato.


POTATO PLANTING TIME: Don't Plant a Problem

Potato seed tubers are often the source of infection for your crop and inspection before planting is well worth the time.  Some problem seed pieces are not going to spread a disease and can be planted.  Others should never be planted.  Here are some common issues.  You can see pictures of these on the web version of this Pest Report, which will be put up a day or so after the email version is sent.

Late Blight - Of course this is the big one. Look at the picture if you don't know what this looks like.

If you are not sure, check with an expert. Besides taking down your potato crop, planting potato seed carrying late blight is the most likely source of a community or state wide problem. Do not plant any potatoes suspected of being infected with late blight.

Fusarium Dry Rot - This is probably the greatest cause of loss in storage. It is also the most common problem seen on seed pieces.  It can result in seed piece decay after planting and result in uneven stands. A slimy rot often develops when Fusarium dry rotted potato seed is planted. This is a secondary infection by bacteria, which take over. Do not plant seed pieces with Fusarium dry rot.

Ring Rot -  This is one of the worst diseases you can get on your farm because once you get it, it is very hard to get the farm clean again, and it spreads very easily by the bacteria clinging to boots, crates, and equipment. Check your seed carefully and discard the whole load if any ring rot is found. In the tuber you will see the disease as a break down of the ring of vascular tissue when you cut the potato. Squeezing the tuber will expel creamy, odorless ooze of bacteria. Planting these tubers will introduce the bacteria to your soil.

Scab - Lesions on the tuber are usually circular and seldom larger than a half inch, but in very bad infections they coalesce.  They may be a cork like layer or pitted. The layer under the lesion is straw colored. Planting these tubers will introduce the bacteria to your soil.

Black Scurf - If you have little black, irregular lumps on the skin of your potatoes that resemble soil but will not wash off, then you have black scurf. This is a disease that is caused by a fungus called Rhizoctonia solani. The black specks are one of the ways the fungus reproduces. They are called sclerotia, which are tight, dry masses of fungal tissue (mycelium) in a resting phase. In the spring the sclerotia germinate and infection of the new potatoes begins. Most commonly, infection of potatoes is from planting potato seed pieces with sclerotia on them, or having done so years ago. Crop rotation is not very effective because sclerotia can survive for many years without a host crop. So, avoid ever planting seed with the disease.

Hollow Heart - Just as the name implies, the center of the potato is hollow. It appears as splitting within the tuber. The inner wall of the hollow part may be white, tan or may be infected with a secondary disease. Hollow heart is not caused by a pathogen but rather by rapid tuber enlargement especially after a period of moisture stress. Potato seed with hollow heart will not spread the disease.

Knobby potatoes - Potatoes with knobs are usually the result of high field temperature and drought or other conditions that cause irregular rates of tuber development. Planting knobby potato seed will not spread the problem.

 

 

FLEA BEETLES IN BRASSICAS

Flea beetles are busy feeding in spring plantings of brassica crops in Massachusetts. Numbers are likely to rise in coming weeks here in Maine as beetles move out of field borders where they spent the winter. Crucifer and striped flea beetles feed on Brassica crops as well as weeds that are in the same family, such as yellow rocket or wild mustard.  [It is a different species of flea beetles that feeds on the tomato family of crops. This is important information when planning rotations of potatoes or tomatoes with Brassica crops or cover crops.]

Flea beetles on broccoli leaf.
Flea beetle trying to get through Proteknet. (www.duboisag.com/en/proteknet-insect-netting.html)
Row covers.

The crucifer flea beetle (Phyllotreta cruciferae) is uniformly black and shiny, about 2 mm in length, while the striped flea beetle (Phyllotreta striolata) has two yellow stripes on its back. Flea beetle adults feed on leaves and stems, resulting in numerous small holes, or ‘shot-holes’. Eggs are laid in the soil starting in late May, and beetle larvae feed on roots. The non-waxy greens (arugula, bok choi, tatsoi, mustard, Chinese cabbage, komatsuna) are preferred to the waxy cabbage, kale and collard types of brassicas. In brassica greens, beetles feed on the whole surface of the leaf, and will continue feeding from the seedling stage until harvest. Waxy crops are most susceptible at the cotyledon and seedling stage and feeding is more limited to leaf margins on older plants.  Some crops simply out grow the beetle pressure and the damage can be tolerated.  No damage can be tolerated in crops such as arugula. 

To reduce and delay flea beetle invasion of spring crops, move them as far away as possible from the fields that were used for Brassica crops last fall. Beetles overwinter in field borders near last year’s crop. Planting the same crop close by to where it was last year ensures a high population in the spring.  The same could be true if you have fields full of mustard weeds.

One of the best ways to protect Brassica crops from flea beetles is to place a floating row cover over the bed or row. It is critical  to seal the edges immediately after seeding or transplanting, because Brassica seeds germinate quickly and beetles rapidly find the cotyledons. Flea beetles can fit through extremely tiny cracks. Edges of the cover must be sealed on all sides using soil, plastic bags filled with soil, or some other method.

Spinosad (Entrust is organic formulation) is proving to be effective in suppressing flea beetles and reducing damage. Pyrethrin (Pyganic EC 5) showed poor to moderate efficacy in trials, and has a short residual period. Yet some growers have reported a good knockdown with this product. You can spray right through the floating row covers and knock down any flea beetles that may have gotten inside.

 

 

OEDEMA (EDEMA)

I often get calls this time of year from folks who fear they have a disease on their tomatoes, or related crops such as tomatillo. It is also a common problem in plants in the cabbage family, and some house plants. They see blisters or bumps on the surface of the leaves, most often the underside. The swellings initially appear pale-green, but they can erupt and turn yellow, brown or even black. Eventually, corky spots appear on the underside of the leaves. Older leaves are more often affected than younger leaves.

Oedema is not a disease caused by a pathogen, but rather is a physiological disorder that develops when a plant absorbs water faster than it can be lost from the leaf surface. Excess moisture builds and the blisters form. This is most commonly induced when transpiration is limited. Transpiration (the natural loss of water from the plant) is reduced by cloudy days , humid conditions in a greenhouse, cool temperatures, low light levels such as when plants are raised on a windowsill in a home, etc. Overwatering under these conditions is commonly the biggest factor causing the problem.

Oedema on tomato. Photo by Tom Zitter, Cornell University.

Leaves affected with edema never clear up, but there are steps to be taken to prevent more of the problem:

* Cut back on watering, but do not let the plants completely dry out.

* Water only in the morning

* Increase the light if it is low.

* Increase ventilation and avoid over-crowding plants


MOFGA's Pest Report - May 7, 2013
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

 
In this report:

Seedcorn maggot

Cutworms

Asparagus pests

 

Seedcorn maggots on spinach.

SEEDCORN MAGGOTS Hylemya platura

 

Now is the time to be aware of the problem. Seedcorn maggot larvae feed on seeds and young seedlings of many crops (corn, beans, beets, peas, spinach, onions, cole crops, etc.). The first symptoms are usually poor germination (or failure of seedlings to emerge), or wilting transplants that have lost their roots to feeding. Symptoms can be difficult to distinguish from other problems, such as damping off due to Pythium or other soilborne fungi, or wireworm feeding. Also, symptoms are similar to damage caused by the cabbage or onion maggot, which I will discuss a bit later in the season when it is time to plant those crops.
 
If seedcorn maggots are the culprit, maggots can usually be found in the soil around and inside seedlings and seeds. The seedcorn maggot is yellow-white, 1/4 inch long, legless, with a wedge-shaped head. The adults look like small houseflies. Seedcorn maggots overwinter in the soil as pupae. In early spring, the adults emerge and lay eggs where they smell organic matter, such as compost or manure you added to a field, decays seeds, etc. The eggs hatch within 2-4 days at soil temperatures of 50F. Research has shown that peak emergence of the first three generations occur when 200, 600 and 1000 degree days have accumulated. Degree days are calculated on a daily basis by using the formula: (Max temp – Min temp)/2 – 39F. You can also refer to a handy calculator at http://www.weather.com/outlook/agriculture/growing-degree-days.
 
The first generation usually causes the most damage. The adults prefer to lay eggs in wet soil that is rich in organic matter. Crop seeds that germinate slowly are more vulnerable to attack. Crops that are planted in wet soil, or when the soil is simply too cool for them to germinate quickly, may be especially susceptible to damage. Last year my earliest planted spinach seedlings wilted within a week of transplanting, and when I pulled one up for examination I saw that it was swarming with maggots.
 
Management strategies:

By the time you see damage, it is too late to control the problem using either cultural or chemical methods. Prevention is the key.
  • Avoid seeding fields (especially wet fields) too early. Seeds germinate more quickly and are less vulnerable in warmer soils. 
  • Disk and incorporate organic matter (such as a cover crop) at least 4 weeks before seeding to give it time to break down and make it less attractive to the flies.
  • Avoid applying manure or unfinished compost in late fall or early spring to heavy soils that you might want to plant early. Lighter, well-drained, sandy soils are less likely to have problems (because they warm up faster than others). 
  • Rowcovers can help – but only if the maggot flies are coming from elsewhere. Damage can occur if the flies have overwintered in the soil and thus end up underneath the rowcovers.
  • If you need to replant, wait at least 5 days if maggots that you find are a quarter inch long; if they are smaller than that, wait at least 10 days to make sure they have pupated and will not damage the new seeds.

 

Cutworms near broccoli.
CUTWORMS (many species)
 
Cutworms are occasional pests of many crops early in the season, including carrots, peas, onions, spinach, broccoli and the list goes on and on. Some years they result in major losses, other years result in no loss at all. They are larvae of a dozen or so different species of night flying moths. They are greasy looking caterpillars that have a habit of curling into a “C” shape when disturbed. Most species that attack vegetables overwinter as partially grown larvae and so can become active very early in the spring when the plants first germinate and are very susceptible. Cutworms hide in the soil during the day and crawl on the surface at night. They feed and cut off young seedlings at the soil surface.
 
Cultural Control: Since most species lay their eggs in the late summer/fall on vegetation, keeping fields clean of weeds and crops in the fall helps. Of course, this goes counter to the recommendations to keep the soil covered cropped, so it is a management decision based on how bad the problem has been. Fall plowing exposes larvae to birds. Cultivating fields in the spring just after vegetation has appeared and grown a few inches, and keeping it clean cultivated can starve the cutworms out before the peas go in. But, in must areas this is not practical because crops need to be planted.
 
Materials Approved for Organic Production: Entomopathogenic nematodes show good efficacy when environmental conditions are favorable. Steinernema carpocapsae has been shown to be very effective against cutworms, although reports are not specifically in pea production. Success with nematodes depends on proper application methods. Be sure to follow the instructions from the supplier carefully. A few suppliers of these insect-attacking nematodes are The Green Spot ( www.greenmethods.com), IPM Laboratories ( www.ipmlabs.com), and ARBICO ( www.arbico.com).
 
Baits: Spinosad or Bt will kill the caterpillars, but getting the pest to consume the insecticide as a sprayed on material before significant damage is done is not likely. However, farmers have reported good results using these materials in baits. The bait is spread on the ground near the plants, or prior to planting to clean out an area.
  • Spinosad - Seduce (OMRI Listed) is a new commercial bait . I have no experience yet with this, so if any of you try it, please let me know what you think. 
  • Bt - A bait made from Bt is often recommended and has received good reports from farmers. This is a method of use of Bt that is not described on the label. This off-label use is permitted by EPA under FIFRA 2ee, but growers should check with their state pesticide regulators about their state regulations. Make the bait by mixing the highest concentration solution of Bt allowed on the label and then mixing in a bit of molasses and alfalfa meal or bran. Then dampen this mix if necessary. Spread the bait along the planted or planned rows in the evening.
 
Common asparagus beetles.
Asparagus beetle eggs.

ASPARAGUS

(Some of this came from the UMass. Vegetable Notes newsletter)

Frost: One of the very first questions I received when I began working for MOFGA many, many years ago turned into an argument. Not a good start, huh?. The guy who called would not believe me that asparagus is frost sensitive. His spears had turned dark, wrinkled and water-soaked and I don't know if I ever convinced him. Perhaps he is reading this.
 
Asparagus, despite its status as a primo early season vegetable, is highly sensitive to frost, ranking alongside cucumber, snap beans, eggplant and tomatoes in the ‘most susceptible’ category. When frosted, spears appear slightly darker green, water-soaked and break off easily. Thawed spears become mushy. Soft-rotting bacteria can enter the damaged tissue. New spears take several more days to emerge, but will. Temperatures below 33 degrees Fahrenheit may damage the spears.
 
Beetles: Common asparagus beetles tend to arrive in mid May. The spotted asparagus beetle generally becomes active somewhat later in the spring, and in my experience is less common (I guess with the names that is not a surprise). These two beetles are closely related and have similar life cycles but it is the common asparagus beetle that is most damaging to the cut spears.
 
Common asparagus beetle (Crioceris asparigi) is blue-black, shiny, smooth and about 6 to 9 mm (1/4 inch) long, with three large yellow, squarish spots with red margins along each wing cover (see picture). Eggs are black, laid standing on end in rows along the spears, and hatch in 3-8 days (see picture below). Larvae are wrinkled, plump, hump-backed, and dull gray with black head and legs. They grow up to 1/3 inch. These larvae feed in spears and in ferns. The larvae do the most damage, and eggs and larval damage makes spears unmarketable. Larval feeding can cause sever defoliation and weaken the stand. When full grown, larvae drop to the soil and pupate underground. New adults emerge in July, feed in ferns, and by September are looking for overwintering sites.
 
Spotted asparagus beetle (Crioceris duodecimpunctata) is reddish orange or tan, with six black spots on each wing cover (hence its other name, 12-spotted asparagus beetle). Eggs are greenish, glued singly on their sides to leaves. Eggs are laid on fronds, not on spears. Larvae are similar to those described above, but are orange colored, and feed almost entirely inside the berries so they affect seed production but do not hurt the plants.
 
Winter habitat: Both species spend the winter as adult beetles either in field borders or within the asparagus field. Sheltered sites such as under bark or in the stems of old plants are preferred. Some burrow into the soil.

Scouting: Early in the season, look for adult beetles, for feeding damage and for eggs laid on spears. Michigan State recommends a treatment threshold of 5-10% of the plants infested or 1-2% of the spears with eggs or damage.

Cultural controls: During harvest, you can greatly reduce the population by harvesting ALL of the spears every harvest day. Pick the field clean to reduce the number of stems where eggs will survive long enough to hatch or larvae can feed and grow up into summer-generation beetles. In the fall remove all of the crop residue and other refuse nearby that may provide shelter for adults over winter, by disking lightly (avoid crown damage) or burning crop stalks and fronds. Maintaining a clean environment in the fall will force beetles to seek shelter outside the field or burrow in the soil, where many predators reside.
 
Biocontrol: The most important natural enemy of common asparagus beetle is a tiny parasitic wasp (Tetrastichus asparagi) that attacks the egg stage. Wasps kill eggs by feeding on them (sucking them dry), and also lay their own eggs inside the beetle eggs. The immature wasps grow inside the beetle larvae, killing them when they pupate. Studies have found >50% of eggs killed by feeding and half of the surviving larvae parasitized. Providing a nearby nectar source such as umbelliferous flowers may enhance wasp populations.
 
Monitoring and chemical control: Scout fields regularly. You may want to treat spears if >10% of the plants are infested with beetles or 2% have eggs or damage. The daily harvest makes treatment difficult because few want to spray anything close to harvest time. Organic options on spears include Surround WP as a repellent, or Entrust.
 
 
- R Hazzard. References: Handbook of Vegetable Pests by John Capinera; 2008-2009 New England Vegetable Management Guide; Eric Sideman, MOFGA; Brian Caldwell, Cornell University

MOFGA's Pest Alert - May 22, 2013
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

In this issue:

Seedling problems

Damping off

 

SEEDLING PROBLEMS

Raising seedlings in a "sterile" mix such as Pro Mix is easy. These mixes are called sterile, however they are not really sterile. They are called sterile because they don't have plant pathogens in them, and that beats my home-made mix. These "sterile" mixes are mixes of pathogen free materials such as peat, perlite, and vermiculite. They often also include synthetic and very available sources of plant nutrients added in just the right amount to get newly germinated plants off and growing. Organic growers do not have the option to use these mixes because of the synthetic fertilizers. We either purchase mixes that are generally based on peat and compost, and other natural sources of nutrients, or mix up our own. Seedling problems are much more likely in organic mixes because of the possibility that the compost may be carrying plant pathogens. In addition, it is much more difficult to predict the availability of nutrients from natural sources because of how that depends on biological activity, which is greatly affected by temperature, moisture and other factors. Many commercially available organic mixes are quite good and consistently free of pathogens, and good with nutrients, but occasionally even these fail. Home made mixes, such as the one I make, fail more regularly. Here are some of the problems I have seen frequently in my home made mix, and occasionally in commercial mixes.

 

Seedling suffering from damping off. Photo by Eric Sideman.

DAMPING-OFF

Damping-off is a disease most commonly seen in young seedling but may rarely effect older seedlings. It is caused by species of fungi that commonly live in the upper layers of soil and when things are not right these pathogens jump at the opportunity to infect germinating seeds and seedlings. The two most common species that cause damping off are in the genera Pythium and Rhizoctonia. There are two types of damping off. The first is one growers often misinterpret because it is pre-emergence damping-off, which rots the sprouting seed before it breaks through the soil. Growers often blame the seed companies for poor seed. The fungus attacks any part of the germinating seed especially the tiny growing tip. Post-emergence damping-off begins as a lesion on the root which extends up the stem to and/or above the soil line. The young stem is constricted by the attack and becomes soft, and the plant falls over and dies.

Damping off cannot be cured but it can be prevented by starting seeds in better conditions (or a "sterile" media). First make sure you are using seeds of the highest quality. Old, mistreated, and weak seeds are more susceptible to damping-off. Anything that slows germination increases the risk of infection. Excessive watering, poor drainage and less then optimum temperatures should be avoided. Allowing the surface of the soil mix to dry a bit before watering helps.

It is possible to "sterilize" your media by baking the mix in the oven at 3500 F for about 45 minutes. The mix should reach 1600 and should stay at that temperature for 30 minutes. Do not allow it to go higher or stay hot longer because overheating kills the beneficial microorganisms and may releases toxic materials. However, many growers prefer not to do this because organic mixes are living systems and often the interactions of organisms in the mix reduces the impact of the fungi causing damping off. In other words, if the damping off pathogens get into a "sterile" mix, they are off and running free of antagonists and competitors.

Cold soil/wet soil: In addition to damping off, cold soil can cause other problems. Growing seedlings on window sills is often a problem because of cold night time temperatures. The roots of plants do not function when cold and plants frequently display symptoms of malnutrition even though the media may have plenty in it. Purple undersides of leaves, stunted growth, pale weak seedlings, etc., are often the results of cold or wet "feet". Trying to grow a tiny seedling in a large container may have the same effect because the plant is just not big enough to use the water, and over watering may be a problem the plant cannot get out of.

Salt: Some composts are high in soluble salts. Even if the salts are nutrient salts such as nitrates, high salts will cause water absorption problems and may prevent seeds from germinating. Salty composts are not a problem in field use because they become diluted with the soil, but in a seedling media it is a real problem. Compost used for media should be the best you can get and should not have salts -measured as conductivity on a compost analysis- higher than 1mmhos.

Carbon:Nitrogen: The C:N ratio is critical for compost used in potting mixes. A high C:N ratio will result in nitrogen lock up, which is a case where all the nitrogen in the media, and any you add with fertilizers, is being grabbed by the bacteria feeding on the carbonaceous material. It is a sign that the compost was made from an improper mix of feedstock, or perhaps is just not finished yet. Compost used to make media should have a C:N ratio of 15:1 to 18:1.

Ammonia: As nitrogen is released from decomposing proteins in a compost pile it passes through a phase where it is an ammonium ion. Unfinished compost will have ammonium ions that may revert to ammonia and kill roots. Ammonia nitrogen in a compost used for a potting soil should be less than 0.1%. Problems from high ammonia can be seen as very weak, dying seedlings, and when you pull them up you see that the roots are brown instead of a nice healthy white.

My recommendation is to get an analysis of any compost you plan to use to build your own seedling mix. The University of Maine Soil Testing Laboratory does compost testing. Just be sure that when you send a sample that you ask for the compost analysis. If you are buying a commercial compost based mix you may want to speak to other growers and see how that brand has worked for them.

DAMPING-OFF IN THE FIELD

Above I discussed damping-off of seedlings. I often receive calls about peas dying just after or just before germinating and I thought I better say that damping off can occur in the field too. This time of year the problem is with peas. The disease is caused by several different species of Pythium, which is a common soil inhabitant that persists in soil in root debris as spores. The species have a wide host range of crops and weeds and so crop rotation will do little to avoid the problem.

During or just after germination the pea seedling begins to show symptoms. The symptoms may be as simple as yellowing and stunting because sometimes only the root tips are infected and this root pruning interrupts growth. Sometimes a soft rot of the stem kills the plant. Sometimes you just don't see any peas germinate. High soil moisture and warm soil temperatures (warmer than optimum for pea growth, i.e., 65-75) favors Pythium. You can't control the weather but you can choose when you plant your peas. If the soil is very wet and warm weather is forecast it may make sense to delay planting a few days for the soil to dry a bit.

There are resistant varieties. The resistant gene is tied to some visual characteristics of the seed. Wrinkled seeds are more severely affected than round seeds. Also, some biological seed treatments such as Rootshield may help.


  

Home | Programs | Agricultural Services | The Fair | Certification | Events | Publications | Resources | Store | Support MOFGA | Contact | MOFGA.net | Search
  Copyright © 2014 Maine Organic Farmers and Gardeners Association   Terms Of Use  Privacy Statement    Site by Planet Maine