Late Blight Recap - 2009
It all started when the big box stores brought diseased seedlings into the Northeast from down south and sold them to gardeners. With ideal weather conditions for survival, spores spread from these plants and by the end of the summer every corner of the region had late blight.
During the season the best organic farmers managed late blight with copper sprays to save their crops and reduce the amount of spores blowing in the wind infecting other plantings. It is important to note that only a few copper products are approved for use on organic crops. Organic growers should contact their certifiers before using any materials to make sure they are allowed.
In addition, farmers and gardeners pulled and destroyed or buried diseased plants to reduce the amount of spores blowing in the wind and infecting other plantings.
Now that the growing season is coming to an end, there is less to worry about. Late blight only over winters in Maine in living crop tissue, i.e., spores do not survive in soil or crop debris or on stakes or in mulch.
The pathogen only survives outdoors here in potato tubers.
So, fall clean up is easy for this disease.
If you do this, and everyone does this, you should be fine and free of late blight.
- Allow all plant debris to freeze.
- Avoid composting or piles that may prevent freezing.
- Next spring use clean potato seed and scout for potato volunteers.
Pest Report - September 3, 2009
LATE BLIGHT: It is late in the season and the calls I receive now are not about saving the crop but about avoiding the problem next year. At last I have good news. The late blight fungus does not live through the winter in the northeast in the soil or on crop debris, UNLESS the crop debris does not die. The spores of late blight are not very resistant to the environment and remain viable only a short time. In other words, late blight survives in the Northeast essentially only in potato tubers. So, with that bit of information you can figure out what to do. Here are some answers to questions you still may have.
SQUASH: HARVEST PERIOD, STORAGE, AND VARIETY SELECTION TO OPTIMIZE EATING QUALITY IN SQUASH (Reprinted from the Umass Vegetable Notes). The record rainfall in June & July, followed by the recent heat, has led to a boom in fruit rot caused by Phytophthora capsici. Given the wet conditions and high disease pressure we’ve experienced this year, it makes sense to get your winter squash and pumpkins out of the field as soon as possible to help reduce the risk of fruit rots. It can be difficult, however, to assess whether or not the fruit is truly ready for harvest – especially in dark green squash, such as acorn varieties. This article aims to provide some insight into judging the ideal time to harvest squash and pumpkins. There are three major species of squash that are grown worldwide – Cucurbita pepo, C. maxima, and C. moschata. The species C. moschata includes calabaza or tropical squash, round to oval pumpkins grown in the Midwest for pie processing, and the popular butternut varieties, highly regarded for excellent shelf life. The species C. maxima includes the large show pumpkins, Golden Delicious type processing squash, Hubbard varieties, and buttercup/kabocha varieties, the latter esteemed for their exceptional eating quality. Lastly, C. pepo is the species having the greatest variation in type, including hard-shelled gourds, summer squash, ornamental pumpkins, and squash. In North America, acorn is the most popular C. pepo squash, but striped Delicata and Sweet Dumpling varieties are known for having good eating quality. The demand for acorn squash has been adversely affected by generally poor quality of popular commercial varieties and the practice of harvesting squash before it reaches maturity. Components of eating quality: People differ in their preference for flavor components and degree of moisture in squash. Nonetheless, connoisseurs of squash usually prefer a relatively dry squash that has a pasty, slightly moist texture after cooking and a high level of sweetness. High sugars not only contribute to a desirable sweet taste, but also mask undesirable flavor components associated with certain varieties. Sugar levels can be estimated easily by pressing juice from a small sample of flesh and measuring soluble solids in the juice with a hand-held refractometer. Relative sugar content is given in units of percent soluble solids (or oBrix). Soluble solids levels of 10% are passable, but generally levels of 11% or greater are considered necessary for good eating quality in squash. The pasty texture of squash is attributable to starch. At harvest starch comprises about two thirds of the dry matter of squash, so squash with high dry matter also have high starch content. Starch provides substrate for conversion to sugars during the latter stages of squash maturation and during subsequent storage. Squash with low dry matter, generally less than 16%, lack sufficient starch levels to produce the combination of pasty texture and degree of sweetness desired for acceptable eating quality. In varieties with low dry matter, starch is rapidly depleted during storage by conversion to sugars, and the texture of the squash becomes watery and fibrous.
- Freezing kills tomato and potato plant tissue so late in the season, when you are no longer worried about the disease spreading, the best practice may be to leave the plant debris on the surface of the ground to freeze.
- Buried potatoes may not freeze and are the most common means by which the disease survives the winter. Next year scout for volunteer potato sprouts and kill them as soon as you see them so they are not a source of spores to start the problem again.
- Use only disease free potato seed.
- Late blight does not survive in tomato seed. Be sure to ferment well if saving your own seed.
- Composting will kill the late blight fungus and spores, BUT it has to be good and hot composting. AND, poor composting is worse than just leaving the debris on the ground. If the compost pile, or any portion of the compost pile gets warm but not hot then you may have diseased tissue not freezing during the winter and the pathogen surviving.
- Cure potatoes for a few weeks after harvest before putting into winter storage in hopes of identifying any that have late blight. Blighted potatoes are likely to rot in storage.
Stages of squash development: To understand how harvest period, storage and variety selection can affect eating quality, it is necessary to understand basics of squash development and maturation. This process includes not only the development of flesh quality, but also the effect of seed development on maintaining flesh quality. Small-fruited varieties of squash, such as acorn, reach close to full size within 15 to 20 days after pollination (DAP) and subsequent fruit set. Dry matter and starch accumulation begins shortly after fruit set, but is most rapid between 10 and 20 DAP and reaches a maximum at 30 DAP. Sugar levels, on the other hand, are very low at 25 DAP, but continue to increase until maturation of squash at about 55 DAP (Figure 2). Some varieties, however, lack adequate sugar levels even at mature harvest, and need to be stored to develop sugar levels suitable for good eating quality. Even though the dry matter of the flesh (mesocarp tissue) peaks at about 30 days after pollination, seed development takes much longer. If a squash is cut open at 20 DAP, the seeds appear to be full size. This is because the seed coat, the leathery covering over the embryo, reaches full size by this time. But if the seed is cut in half, the embryo is actually barely visible at this time, being about an eighth to a quarter of an inch in length. The embryo expands rapidly and largely fills the seed coat cavity by 35 days after pollination. However, dry seed biomass (seed fill) continues almost linearly until about 55 DAP. Thus, a squash fruit can be considered to reach full maturation when seed development is complete at about 55 days after pollination. If fruit are picked immature, seed development continues in stored fruit at about the same rate as in fruit left on the plant. Seed development in an immature, detached fruit occurs at the expense of depletion of nutrient reserves in the fleshy tissue, thereby reducing dry matter (mostly starch) and lowering eating quality. Post maturation changes occur in stored fruit. There is a progressive moisture loss during storage, so fruit fresh weight decreases. Respiration consumes carbon in the form of sugars, and starch continues to degrade to replace the sugar consumed by respiration. The eating quality of squash varieties with low sugar at harvest will initially be enhanced in storage because sugar levels increase. Eventually, however, long storage time will deplete starch levels to a point where the texture of the squash is compromised. To maximize shelf life, squash should be stored at 55 to 60° F with moderately high relative humidity (50 to 70%). Because seed maturation is not complete until 7 to 8 weeks after fruit set, it is important to maintain a healthy plant until at least 50 days after fruit set. This insures a continuous supply of photosynthates (carbon source produced from photosynthesis) to the developing fruit. Seeds are the primary sink for assimilates such as sugars, so if photosynthesis is impaired by disease or insect feeding, nutrients for the developing seed are withdrawn from the flesh, depleting starch levels and lowering eating quality. Harvest period and eating quality: Because fruit and seed development are similar in all three species of squash, their recommended harvest periods are similar. Butternut squash do not reach their characteristic tan color until late in development, so premature harvest before starch accumulation and seed fill are complete is generally not a problem. With kabocha varieties, it is actually desirable to harvest them before complete seed maturation, about 40 to 45 days after fruit set when the fruit are still bright green. New Zealand studies indicate that rind hardness is maximum around 40 DAP, so fruit harvested at 40 days suffer less damage to the fruit surface, and in turn, less chance for disease entry during subsequent storage, than fruit picked during later stages. Kabocha squash are also susceptible to sunburn damage and changes in rind color to brownish green, so it is best to harvest the squash before fruit are exposed to direct sun as the vines die down. Kabocha squash have a high dry matter content, usually 20 to 30%, and a small seed cavity, so that any seed maturation following harvest has a minimal effect on depleting starch reserves in the flesh. Acorn squash present the most difficult problem with respect to determining harvest time. Most modern acorn varieties not only reach near full size within two weeks after fruit set, but also develop a dark green to black mature color. For this reason, acorn squash harvested for the large wholesale markets are often picked immature. This can be easily observed in supermarkets by noting that the rind on the ground side of the squash is light green or light yellow rather than dark orange coloration of mature fruit. If these immature squash are sampled, they are found to have very low sugar levels. If such immature squash are left in storage, sugar content will increase, but the starch will be depleted both by respiration and movement of nutrients from the flesh to the developing seed, and this results in poor eating quality. The problem of poor quality in prematurely harvested squash is further exacerbated because most commercial acorn varieties and many of the newer striped varieties have inherently (genetically determined) low dry matter and starch levels. How do you determine when to harvest? Most acorn varieties are semi-bush and set most of the crown fruit within about a week period. Modern hybrids tend to produce some female flowers before male flowers appear and these usually abort unless there are other varieties of C. pepo nearby supplying pollen. But this is shortly followed by a period of both male and female flowering and fruit set. Some later fruit sets will occur on runners, but these fruit are usually undersized and lack quality, and so should not be harvested and sold. These late set fruit are a drain on photosynthates, and pruning these fruit off of the plant can actually increase quality of the crown set fruit. By noting the initial flush of male and female flowers on a semi-bush squash cultivar, a grower can estimate the approximate time when fruit set occurred, and delay harvest until about 50 days or more from the fruit set period. Another approach is to check the ground spot on the fruit, and not harvest fruit until the spot turns orange. Some of the newer striped varieties of C. pepo will show some color changes with maturation, but the color change, say from white to tan between the stripes or stripes changing from green to orange, may occur well after the fruit are ripe enough to harvest. So with these, I think that it is better to keep track of the approximate date of fruit set. However, if you observe a color change that correlates with maturity in a particular variety, then you can use that as a harvest indicator. How about variety selection? That is a tough call. I have found that most modern hybrids being commercially sold lack the eating quality of a good Sweet Dumpling or Delicata squash. UNH has developed some high quality acorn and sweet dumpling type varieties that are being released to the seed industry. High Mowing Organic Seeds offers a UNH-developed, sweet dumpling hybrid, Sugar Dumpling, which also has intermediate resistance to powdery mildew. Johnny’s Selected Seeds is in the process of producing one of my PMR mini-acorns, and currently sells an acorn hybrid, Tip Top, that has good eating quality. Cornell Bush Delicata is another variety in this class with good eating quality and powdery mildew resistance. There are several other varieties available that have reasonably good eating quality, so growers will just have to evaluate them to determine if they fit into their particular farm and marketing situation. - Brent Loy, Department of Plant Biology University of New Hampshire.
IMPORTED CABBAGE WORM. 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 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 that 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.
ALTERNARIA LEAF BLIGHT OF CARROT: The lesions on the leaves start along the margin as spots but they grow together and the leaflets shrivel and die. This disease effects the older leaves much more than the younger leaves and so it is common to see healthy young leaves growing through the mass of dead old leaves. The pathogen survives on seed so be sure to buy seed from a good source. It overwinters on crop residue and on related weeds. It is spread by wind and water, mostly happening when the leaves are wet long periods. A two to three year rotation and good sanitation are important. For late season carrots that have healthy young foliage a boost of nitrogen now may help carrots to size up before harvest.
Pest Report - August 12, 2009
LATE BLIGHT: What to do with a field infected with late blight
[Reprinted and modified a bit from an article by Becky Grube Sideman, UNH Cooperative Extension, Sustainable Horticulture Specialist]
Late blight is now in potato and tomato fields throughout the state. From what I have heard, those using preventative fungicide programs have kept the disease at bay thus far, but many who did not apply fungicides are having fields go down. Once symptoms are widespread in the field, it is the time to cut your losses and kill the plants to prevent the disease from spreading into other fields or high tunnels. For tomatoes, this will mean a crop loss. For potatoes, however, it may still be possible to get a decent crop.
Killing potato vines before harvest will reduce the chance of infecting tubers. Late blight spores do not survive on dead vegetation. Vines can be killed by mowing, burning, or using dessicants (herbicides). Mowing can be a challenge in a hilled potato field. After killing the vines, wait at least two weeks before harvesting to give the vines time to die completely. This helps avoid dragging the potatoes through spore laden foliage. The ground is a good place to store potatoes while waiting to dig them; it is cool, moist and dark, and the skins will harden on those tubers that are not already infected. That said, ground storage poses some risks: wireworms, grubs, and rodents may find and feed on potatoes, and the longer the tubers stay in the ground, the higher the risk. Digging test hills in a few locations to check for evidence of these pests may help you evaluate the tradeoffs.
Harvest when soil is not excessively wet, and do not wash tubers. Tubers should be dry when placed in storage. Remove any obviously infected tubers before storage. Curing tubers (10-20 days at 50-60 F, 95% relative humidity) generally heals wounds and help tubers store longer. These conditions will also cause those tubers infected with late blight to decay rapidly, so that you can cull rotted tubers. In storage, forced air ventilation through the storage bin can help minimize spread from tuber to tuber. Storage of potatoes with small amounts of late blight should be at 38 F to retard late blight tuber rot. If you must wash tubers before sale, organic growers can use Storox (Oxidate) or chlorine (dilute to 4ppm before discharge) at labeled rates in wash water.
Some common questions…
How do I get rid of infected tubers? If you end up with infected tubers, it’s important to dispose of them properly. Do not make cull piles. In a cull pile, the late blight pathogen can survive the winter and be a source of inoculum early next year. No matter how you dispose of tubers, carefully monitor for (and destroy) and volunteer sprouting potatoes next spring. Options for safe disposal include the following:
Burial. Trenches filled will culls should be covered with at least 18” of clean soil to prevent tubers from sprouting.
Livestock feed. This can be done during late fall and winter, when freezing temperatures will kill tubers that are not eaten within one day. During summer, this is not recommended unless all culls are eaten within one day.
Composting. Compost piles must be turned and mixed routinely and may require special equipment for large piles. The University of Maine fact sheet ‘Composting Cull Potatoes’ has more detailed information: http://www.umaine.edu/umext/potatoprogram/Fact%20Sheets/Composting%20Cull%20Potatoes.pdf
Spreading. Cull potatoes may be spread during late fall and early winter on fields that are not destined to be potato fields the next year. Culls should be left on the surface to ensure they are killed by freezing temperatures.
Can I save my potatoes for seed? If you have late blight symptoms in your field, saving seed tubers from that field is very risky. Even when there’s no evidence of tuber blight, up to 20% of the tubers in a seed lot can have latent infections with the late blight pathogen. Tubers with latent infections can cause foliar symptoms very early in the season, and set you up for needing to apply foliar late blight fungicides. The best way to avoid seedborne transmission of late blight is to purchase certified disease-free seed next year and make sure to scout for and remove any volunteer potato plants that come up next spring.
My tomato plants are going down, but fruit look OK. Can I harvest and sell healthy fruit? Once plants are infected, symptoms continue to develop in fruit even after they are harvested. In previous years, it has not been uncommon to see infected fruits in markets. Fruits harvested from infected plants are definitely at risk of developing symptoms during storage before they are sold and consumed.
Information compiled from many sources including Universities of Vermont, Maine, Massachusetts, and Idaho.
DOWNY MILDEW UPDATE. (Reprinted and modified from the University of Massachusetts Vegetable News letter). Downy mildew is being reported in Massachusetts. This makes it very possible that downy will be showing up in your fields soon. Cucumbers are especially at risk. SCOUT OFTEN. Downy mildew first appears as yellow polka-dots on the leaves. These yellow spots quickly turn into square or almost square brown lesions that are restricted by the small leaf veins. Next the older leaves begin to curl upwards at the margins and finally all the foliage in the field dies. If you see the yellow polka-dots or brown mosaic-like lesions you will need to respond quickly with an effective material because it only takes a week to 10 days for the foliage to die. Resistant varieties, selecting sites with good air movement and other practices that promote quick drying and drip irrigation rather than overhead are the most important cultural practices to avoid downy mildew. Copper compounds are probably the best material organic growers have, but they are not very effective. See the ATTRA publication for more information on copper and other management ideas (http://attra.ncat.org/attra-pub/downymildew.html).
BLACK ROT OF BRASSICAS. Black rot is one of the most important diseases of brassicas world wide and is much more of a problem in warm, humid climates than in the cool northeast. Still, it is very common here and does result in crop loss. The disease is caused by a bacterium called Xanthomonas campestris. The initial infection is most often through seeds and infected crop debris. The bacteria are spread by rain splash, insects, workers, and equipment. The symptoms are irregular, dull yellow areas along the margins of the leaves that expand in a "V" shape (see picture on MOFGA website). The veins in the lesions often look dark. Sanitation is the key to avoiding this disease, but the problem is that sanitation is most important during seed production. Buy seeds from a reputable source. Begin sanitation when raising seedlings. Any yellowing seedlings or plants with "V" shaped lesions should not be planted in the field as they will serve as a source of bacteria that may spread to the whole field. There are resistant varieties. Crop rotation (3 years) is important so if you have this problem pay attention to which fields and clean equipment so you do not drag crop debris to new fields. Avoid overhead irrigation, but of course this year that would make no difference. Do not use manure from livestock that have been fed diseased Brassicas on fields intended from Brassica crops. Hot water treated seed is recommended. For cabbage and Brussels sprouts soak seed for 25 minutes in 122 F water, and for broccoli and cauliflower soak for 20 minutes. Precise time and temperature control is essential to minimize damage to the seed.
Pest Report - July 22, 2009
LATE BLIGHT: This is still the hot topic. It is now reported pretty much in all the corners of the state. Some areas are hot spots with lots of reports and others have only one or two growers reporting. We in Maine are not alone as it is all through New England and New York. Previous Pest Reports and Extension publications have dealt with how to handle it. Steve Johnson has recently put together a guideline for mixing small quantities to spray small areas, and also included a discussion of Worker Protection Standards for commercial growers. Download Steve's document.
LEAFHOPPERS: Potato Leafhoppers (PLH) have made it to Maine. I have just received a report of them in Wells on beans and they have been in southern New Hampshire for a while. They are likely to be moving north so be on the lookout. They also feed on potatoes, strawberries and alfalfa.. PLH does not over winter anywhere near here. They over winter way down south and leapfrog up here in mass migrations. The first to arrive are females, and they are usually carrying fertilized eggs when they get here. Then there are a few generations over the growing season before the cold north winter kills them.
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. The leaves first get pale, then yellow and then brown from the edges. Then the plant dies. The symptoms are called hopper burn.
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 and watch one of the white-looking bugs land. The nymphs are similar to the adult, but have no wings and are smaller and 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 leafhopper.
The adults are flighty. When you brush your crop you will see them fly up. If there is a cloud, you are in trouble. If there is only one or two in a row of plants your crop will probably not be hurt badly. That is why researchers have developed a threshold before treatment is recommended. For example, on beans a population equal or exceeding an average of one nymph per leaf, or fifty adults per ten sweeps with a net means it is time to spray.
Crop rotation does nothing for you since they are coming from far away. Covering you 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 that well. 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.
MEXICAN BEAN BEETLE: (modified from an article By Ruth Hazzard - reprinted from the Umass Vegetable Newsletter). If you are having Mexican bean beetle problems now then next year plan for your management in the spring. It would have been good for me to give you that advice last winter. If these destructive insects have historically been a problem on your farm, you will very likely see them again every year. They may be pests on snap beans, soybeans, and lima beans. While they are not a pest on every farm, some farms report significant damage from these pests and have to take action to prevent crop loss. Using biological control can replace 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 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 increasing in numbers.
|Adult Mexican Bean Beetle.
The only material for organic growers is Pyganic and its efficacy is at best fair.
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. (http://www.state.nj.us/agriculture/divisions/pi/ prog/beneficialinsect.html4).
|Mexican Bean Beetle Larvae.
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. 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. The release rate should be at least 2,000 adult wasps per field for less than an acre, or 3,000 per acre for fields of one acre or more. The 2007 cost from NJDA was $30 plus shipping for 1,000 adults, or $15 for 20 mummies (pupal parasites inside dead MBB larvae) from which about 500 adults will emerge (call for current prices). 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. Contact information for New Jersey source: Tom Dorsey, 609-530-4192; address; NJDA, Phillip Alampi Insect Lab, State Police Drive, W. Trenton, NJ 08628. You’ll also get advice on how to use the wasps from this office (website:http://www.state.nj.us/agriculture/divisions/pi/prog/beneficialinsect.html). Pediobius is also available from the following suppliers: Green Spot Ltd., NH., www.greenmethods.com 603-942-8925; IPM Laboratories, NY 315-497-2063; ARBICO, 800 -827-2847 (AZ), http://www.arbico.com/; Network (TN), 615-3704301, http://www.biconet.com/; Rincon Vitova (CA), 800-248-2847, http://www.rinconvitova.com/
July 13, 2009
: No questions now. Late blight is showing up around the state in potatoes and tomatoes and we should all be on the look out and responsibly handle it. Remember, late blight is a community problem because if it is in your field then you become a source of spores effecting your neighbor.
Spores are reported to be blowing in the wind now, but that does not take you off the hook. We all have to be responsible and keep the number of spores in the air to a minimum.
Look at the previous Pest Report for a description of the disease symptoms and biology of the pathogen. For really good pictures see:
If you positively ID late blight in areas of your field, then pull those plants, bag them (DO NOT JUST PULL AND THROW ON THE GROUND!), and dispose of them so they are not a source of spores. Do this for an area about 5-10 feet in diameter around the plants showing symptoms. Then, spray the field with an approved formulation of copper fungicide. Some growers are doing both an Oxidate spray, and then a copper fungicide spray.
There are lots of diseases of potatoes and tomatoes showing up now after all that rainy and damp weather. Mostly what I am seeing is Botrytis and early blight. If you are not sure that your diseased plants have late blight feel free to email me a picture, or contact your Extension office.
ONION THRIPS: Thrips are one of those problems that you rarely spot the insect but see the symptoms of their feeding first and then start searching. I have had reports of them being out this year in onions in central Maine. These insects feed on lots of different kinds of plants and often are there but in small numbers so can be ignored. Sometimes the populations get large and can really take down an onion field or at least greatly reduce your yield.
The onion thrips feed on onion leaves by rasping the tissue and sucking juices. The feeding leaves white streaks that get larger if feeding continues, and white patches on the leaves develop. I am surprised to hear that this pest is a problem this year because it tends to be a problem in dry years, and heavy rains often wash the pest away.
If you see what you think is the damage, then look for thrips in the tiny spaces between the leaves. Thrips are very small, about 1mm.
Crop rotation can help as can sanitation and weed control. The pest overwinters as an adult in crop refuse. Infestation often begins on field borders if the pest overwintered in weeds or nearby fields and then migrated to the new onion field. Mowing fields of alfalfa can drive the pest into the onion field. Heavy irrigation may wash the thrips off. If you have them bad and need to spray, Entrust should work.
ROSE CHAFER: The rose chafer is in the same family of beetles as the Japanese beetle and has a similar life history. The adult is out now and voraciously feeding on many different crops such as rose, raspberries, apples, grapes and some vegetables too. They skeletonize the leaves and are feeding on blossoms and young fruit too.
The adult is a half inch long, gray-tan beetle with a reddish-brown head. The adults are mating now and will lay white, shiny eggs in the soil soon. The larvae are white grubs that live in sod feeding on roots, especially on sandy ground. The life span of the adult is only about three weeks so you may just want to wait them out. But if your population is large you may loose your crop while you wait.
Crop rotation will not help because they are good fliers. You may be able to control grubs with beneficial nematodes, but that is likely to help little with controlling adults because your neighbor's sod ground will be a source even if yours is not.
Hand picking or knocking the critter off the leaf into a jar of water works well for small plantings.
Pyganic and Surround seem to do little to deter adults. Rotenone may work, but there are no formulations permitted in organic production and its EPA registration as an insecticide has been dropped.
I have heard from a grower that neem oil works well, especially a neem and diatomaceous earth combo. Has anyone else tried that with success? Are there any other suggestions?
Alert to Potato and Tomato Growers
[Reprinted and modified from a posting by Meg McGrath,
Department of Plant Pathology and Plant-Microbe Biology, Cornell University]
Late Blight Found in Potato in Suffolk County, on Long Island, NY and in PA
Late blight is spreading quickly north. Some large, nationwide retail stores are selling seedlings already infected, even in Maine. If you bought seedlings at one of these stores check you plants and keep on checking.
Symptoms of late blight were confirmed on 23 June in a commercial field of potatoes in Riverhead and on 24 June on tomato in a home garden in Wading River. Rainy, cloudy conditions have been providing favorable conditions for the pathogen to successfully be dispersed long distances and for infection. Clouds protect spores being dispersed in wind from the killing effect of uv radiation.
This is the fourth year late blight has occurred on LI over the past 21 years. The earliest it had ever previously been detected was 26 Aug.
All growers, including gardeners, should thoroughly inspect their potato and tomato plantings because this can be a very destructive disease when not managed, quickly killing foliage and rotting tomato fruit and potato tubers, AND be a source of spores spreading the disease to other growers. Late blight was the cause of the Irish Potato Famine.
Classic symptoms are large (at least nickel sized) olive green to brown spots on leaves with slightly fuzzy white fungal growth on the underside when conditions have been humid (early morning or after rain, or if it is dry you can induce it for identification by putting an infected leaf in a plastic bag over night). Sometimes the lesion border is yellow or has a water-soaked appearance. Leaf lesions begin as tiny, irregularly-shaped brown spots. Brown to blackish lesions also develop on upper stems. Firm, brown spots develop on tomato fruit. Photographs are posted on the web at www.mofga.org . If you believe you have the disease, get a sample to your local Extension office.
If late blight is found in a localized spot in a field or garden, promptly destroy all symptomatic plants plus a border of surrounding plants to eliminate this source of inoculum. Physically pull, bag and get rid of affected plants. Do not just drop in field as they will still be a source of spores. If disking is used to destroy a whole field, the crop should first be sprayed with fungicide first because of the potential to move spores on equipment especially while driving out of the field, and the equipment should be pressure washed afterwards.
Management in organic crops. Apply fungicides preventatively, using a 5-day schedule when conditions are favorable. Copper is effective for protecting a crop, but copper has been found to be ineffective when used as the sole practice for controlling late blight once it has started to develop. Other OMRI-listed fungicides labeled for late blight include Sporatec, Sonata, Serenade Max, and Companion. It is important to scout regularly and promptly destroy affected plants when found to reduce the amount of inoculum in a field. It is recommended that plants with symptoms be physically pulled up plus a few border plants, preferably on a bright sunny day when possible, then tarp the plants; spores will be killed by sunlight and also heat under the tarp. Scout daily thereafter for a few days to see if more plants develop symptoms. Clean after working in infested fields to avoid moving spores on equipment and workers. As soon as harvest is complete disk down field. And next year scout for and destroy any volunteer potato plants.
Some of this information on management was provided by Dr. Steve Johnson, University of Maine Cooperative Extension, and Dr. Tom Zitter, Cornell University.
Pest Report - June 19, 2009
STUNTED LITTLE YELLOW PLANTS, WILL THEY RECOVER? It depends. The cold nights and cool days of June have let little biological activity in the soil happen and nitrogen, in the organic form that most of us organic growers use, is not being made available to the crops. The plants are showing nitrogen deficiency. They probably will
recover when the soil warms and the seed meals and compost release the nitrogen.
But now we may have to deal with another cause of low nitrogen. Roots of nearly all species of plants must have oxygen available to them and when the soil becomes waterlogged all of the air spaces are filled. Roots stop absorbing nutrients, especially nitrogen. If it stays wet long enough the roots die.
The wet weather will also compound the problem with the way nitrogen behaves in the soil. Nitrogen can be found in soil in many forms such as the gas nitrogen, as part of the proteins in organic matter and as ions such as nitrate, nitrite and ammonium. Most plants can only pick up the nitrogen when it is in the nitrate form and some (e.g. blueberries) when it is in the ammonium form. In soil that has air and moisture (but not too much), nitrogen cycles around these different forms by biological activity and some is always passing through the nitrate form and is available to crops. When the soil is too dry, too cold or too wet the cycling stops or can even change direction so the nitrogen is lost from the soil either by leaching or by reverting to a gas form and goes out into the atmosphere. This may happen all over a field when it is wet like this weekend, or only in portions of fields where water puddles.
The rains of June have come again and some of the nitrate may lost by simple leaching. If the rain continues, the soil may became waterlogged and anaerobic, and the nitrate may revert to nitrogen gas and be lost. If most of your nitrogen is in the nitrate form at this time, it may be gone. Folks who use chemical fertilizers will probably have to reapply it. The nitrogen that was in organic forms such as seed meals, fish meal, compost and livestock manure probably will still have much of the nitrogen left because the soil became cold and anaerobic before the bacteria converted the organic nitrogen to soluble nitrate. Farmers just have to wait for the air spaces to reappear in the soil and the bacteria to get to work. Of course, this should have happened in May. So it may be wise to supplement your crops with a bit of available nitrogen.
Spring in New England is nothing but fun.
Cutworm are still a real challenge for some growers, especially for small transplants and carrots and onions. Cutworms are the caterpillar of a few different species of night flying moths. Some of the species fly in very early in the spring and others arrive in the fall. They lay eggs at the base of plants (weeds and cover crops as well as your cash crop). The eggs hatch into tiny, dark gray, greasy caterpillars that feed at night. Some species just simply cut off your plants just about at ground level. Other species climb up and cut off leaves or eat notches out of them. The caterpillars can be found in the soil by digging around near the damaged plants. They curl up into a "c" shape when you handle them.
The big problem is you never know whether it will be a problem or not. On a small scale, Dixie cups with the bottoms cut out placed around a transplant make a good barrier.
One method that works on a large scale but is usually not practical is to starve them out. If you can keep a field completely free of ANY growing plants (weeds or crops) for a few weeks after they hatch then they will die.
I have received good reports about making a bait from wheat bran, a Bt solution and molasses and then sprinkling it or making patties and putting the patties along the row of effected crops. This year I tried using alfalfa meal instead of bran and I really think it works. No, I don't have a specific recipe. This idea is a copy of baits that were recommended fifty years ago, but then with materials way to frightening to mention. I suggest you make the most concentrated solution of the Bt allowed on the label. A solution of Entrust would work too. Make the solution of Bt and molasses and then add the bran or alfalfa meal to make it damp. Put it out in the evening because the cutworms feed at night and the Bt breaks down quickly in sunlight.
I have also heard very good reports from folks who have used parasitic nematodes. The best results for cutworms is achieved when a combination of two types of nematodes are applied in a mixture because the different species work different levels in the soil and attack the cutworms both while they hide deeper in the soil during the day and when they move up at night. A mixture of Heterorhabditis bacteriophorea (Hb) and Steinernema carpocapsae (Sc) has essentially eliminated cutworm problems for some of our growers. The nematodes are usually shipped on a sponge ready to mix with water and apply to the soil. It is important not to let the soil surface dry out shortly after application. 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). It may be too late this year for nematodes to help, but remember for next year.
MANAGING STRIPED CUCUMBER BEETLE IN VINE CROPS
(Reprinted and modified from Umass Vegnotes, June 4, 2009)
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, 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 and delayed plant growth. The striped cucumber beetle vectors Erwinia tracheiphila, the causal agent of bacterial wilt, and this can be more damaging than direct feeding injury. 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. The higher beetle density during early plant growth, the more severe the incidence of wilt. Male beetles that discover a host plant will release an aggregation pheromone that calls others to their spot. Groups of beetles feeding, wounding and defecating on a single plant are more likely to transmit disease, and to acquire the pathogen and transmit it to other plants.
Cultural Controls: Crop rotation. Because beetles spend the winter in field borders close to last year’s crop, planting into the same field encourages rapid invasion by high numbers of beetles. Rotating to a field at a distance from last year’s cucurbits reduces beetle numbers significantly. Of course, crop rotation has many other benefits as well – in vine crops, it is critical for disease management. Any barriers between the fields – woods, buildings, fallow fields or other crops, roadways and waterways – help delay the arrival of beetles.
Cultural Controls: Using Transplants. Several studies in the Northeast have shown that three-week-old transplants, set out in the field at the same time as a direct-seeded crop, will produce not only earlier but higher yields. These studies were done with both summer and winter squashes. Transplants have multiple benefits. Germination of untreated seeds in cool soils can be spotty, while transplanting ensures a good stand. Transplants provide a jump on the weeds. Plants are bigger when cucumber beetles arrive so that they are less vulnerable to both feeding damage and to wilt. An insecticide or repellent can be applied to flats before plants are set out, making it less costly. Planting dates are more flexible – for some crops, it may be possible to delay planting until late June and avoid the worst of the beetles. Plants can be held inside to avoid late frost or wait until fields are dry (or wet) enough to plant. Of course, it is not advisable to hold transplants too long. If they are already flowering or have been stressed when they are set out, they tend to develop into small plants with early but small fruit. Standard seedling production methods work well for vine crops, but large cell sizes (72, 36 or 24) or peat pots are recommended as roots should not be disturbed when transplanting.
Cultural Controls: Floating, or spun-bonded, row covers are very effective barriers that keep beetles off the crop during the critical early growth stage. They have the added benefit of enhancing growth and reducing wind damage in the early season, for an earlier yield. Studies have also shown an increase in yield with row covers. Covers must be removed at flowering to allow for pollination. Wire hoops are very helpful, to prevent damage from abrasion; these are usually used on single rows, but can also be used under wide sheets of 15 or 25 or 50 feet. Black plastic adds warmth and solves the problem of weed management under the covers.
Thresholds and foliar controls. Beetle numbers should be kept low, especially before the 5-leaf stage. Scout frequently (at least twice per week 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, 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. Proper timing is key.
Organic insecticides. OMRI-list insecticides available for use in organic cucurbits include kaolin clay (Surround WP), pyrethrin (Pyganic Crop Spray 5.0 EC), and spinosad (Entrust). Pyrethrin is a short-lived contact toxin that has shown poor results on SCB in trials. Spinosad acts both as a contact and a stomach poison and has shown reasonably good results in recent trials. See last week’s issue for more details. Surround WP should be applied before beetles arrive because it acts as a repellent and protectant -- beetles do not “recognize” the plant and so do not feed -- not a contact poison. With direct seeded crops, apply as soon as seedlings emerge if beetles are active. Transplants can be sprayed before setting out in the field. Surround can also be used on the main crop of a PTC system, creating a “push-pull” dynamic.
Perimeter trap cropping. This strategy saves time and money – and it works! See http://www.umassvegetable.org/soil_crop_pest_mgt/insect_mgt/PerimeterTrapCro
(Ruth Hazzard, University of Massachusetts)
ASIATIC GARDEN BEETLE
The Asiatic Garden Beetle is a native of Japan and China where it is not an important pest. I am getting more and more reports about problems here recently. The pest overwinters in the soil as a grub feeding on the roots in sod ground and weedy gardens. The larvae 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 have had 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.
Pest Report- June 14, 2009
The rain has brought out these odd creatures and growers are calling to ask if there is need to worry. No, horsehair worms are not harmful to humans, pets or plants. In fact, they are potentially beneficial in that they are parasites of insects.
Horsehair worms are closely related to nematodes. They are similar in appearance in being long, thin and round. And similar to nematodes, they whip and thrash when handled because of the prominent orientation of longitudinal muscles. They are thin like hairs and are long (2-6 inches is common; see photo on the MOFGA website).
The worms you are finding now are free-living adults. There are a few hundred different species and range in color from white to brownish black. They are common soil inhabitants but are most commonly seen after rain and often are found in wet soil or puddles.
The juveniles are the parasite. The preparasitic worms are minute, and infect their host when they are accidentally ingested. They cannot penetrate hosts from the outside. This group, called Nematomorphs, infect insects, including crickets, cockroaches, beetles, mantids, and grasshoppers, but also spiders and sowbugs.
COLORADO POTATO BEETLE
See the last issue of the pest report for the discussion. This is a reminder to get out there and scout. Remember, this pest is known as the potato beetle but loves eggplant even more than potatoes.
CUCUMBER BEETLES ON MY POTATOES?
No. Those are not cucumber beetles. Potatoes, tomatoes 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.
The three most common problems with tomatoes grown in the field in Maine are Early Blight, Bacterial (Spot and Speck) and Septoria Leaf Spot. It is early, but it is time to start looking if you want to get some control on them.
Bacterial Speck starts as dark brown to black spots on leaves that later develop yellow halos around the area affected. On the fruit black specks develop that rarely get larger than 1 mm. Bacterial Spot starts as brownish, circular spots that may become as large as 3mm and irregular. The diseases may be seed borne and may be carried over in weeds. High humidity and low temperatures favor bacterial speck.
Early blight of tomato is caused by fungi and starts on the lower leaves as small circular spots that have a target appearance of concentric rings. Leaves develop yellow blighted areas as the spots enlarge. Later the tomato fruit may rot on the stem end. The disease is carried over on tomato residue in the soil and can be seed borne.
Septoria Leaf Spot is a fungal disease that starts as spots on the lower leaves that have a dark brown margin and a tan center, and no target appearance. Rapid defoliation can occur.
Crop rotation is the first line of defense from these problems. Sanitation is important. Do not grow tomatoes near cull piles of last year's crops. Trellising, staking, cages, etc help but remember to disinfect if they were used last year (a 12X dilution of household bleach is effective). Prune off diseased lower leaves, but it is especially important to disinfect tools if the problem is one of the bacterial diseases. Avoid working in the crops
when they are wet. Scouting is going to be important this year. With this wet weather we have, start early and if you decide to use a material, copper is probably the one most effective for us organic growers. If you decide to do it, start at the first sign of problems and you need to keep the new tissue covered. This year because of problems with the way inert ingredients are regulated in the NOP Rule and the changes in the way EPA
categorizes inert ingredients, Champ WG is one of the very few permitted formulations of copper for certified growers. Be sure to check with your certifier if using something other than that.
CATERPILLARS AND MAGGOT FLIES IN BRASSICA (Reprinted and modified from U. Mass Vegetable Notes, June 11, 2009)
Early cabbage and broccoli crops will soon begin to form heads, which means caterpillar injury will have more impact on the marketability of the crop. They have found both diamondback moth caterpillars and imported cabbageworm in the Connecticut Valley. Though cooler temperatures slow them down, these pests are actively feeding down there and its time to start scouting your fields. In the early season the numbers tend to be lower than late season, but keeping the first heads clean is key.
Growers have reported maggot eggs and damage on transplants set out in late April and early May. By now, egg laying by the first flight of maggot flies is likely to have subsided. Dry conditions may help reduce survival of eggs and maggots, but cool temperatures favor it.
||Imported Cabbage Worm.
||Diamondback moth caterpillar.
||Diamondback moth adult.
Imported cabbageworm; cabbage butterfly (Pieris rapae). This familiar white butterfly can be seen in daytime fluttering around cole crop fields. Each forewing has a dark border and one or two round black spots. Eggs are laid singly on the underside or top of leaves, about 1/8 inch in length, light green and slightly elongated, standing upright. The caterpillar, called imported cabbageworm, is gray-green, slightly fuzzy, and sluggish. Feeding and resting occur on the underside of leaves, and larvae feed more heavily in the head of cabbage or broccoli as they grow. The chrysalis (pupa) will be green or brown, smooth with three pointed ridges on its back, and attached to a leaf. There are 3-4 generations per year.
Diamondback moth (Plutella xylostella) caterpillars are smaller, light green, appear more segmented and more pointed in shape. When disturbed they wiggle vigorously and may drop off the plant on a string of silk. Feeding causes small, round holes and tends to be spread across the foliage and not necessarily concentrated in the head. The adults are tiny (<1/2 inch), light brown, and rest with their wings folded together like a tent. They overwinter in crop residue, but not thought to overwinter in Maine. The enter our region by migrating from southern states.
Field Scouting for caterpillars: It is especially important to check cabbage or broccoli plantings as they begin forming heads. Greens such as collards, kale, and Chinese cabbage should be scouted earlier, since all leaves are marketed. Feeding damage can be found on the underside of leaves or in the center of the plant where heads are forming. Look for tiny feeding holes, clustered together. Often it is easier to spot the feeding damage first, and then find the caterpillar. Check 25 plants throughout the field and note how many have one or more caterpillar (i.e., are “infested”), then calculate the percent of plants infested. Spray if the following threshold is reached: 35% of plants ‘infested’ for Cabbage & Broccoli, Cauliflower before head formation begins and 15% during head formation for cabbage and broccoli and 10% for cauliflower; 10-15 % for kale, collard and other greens. These thresholds are based on research that showed that spraying whenever this level of infestation is reached results in 98-100% clean heads, the equivalent of weekly sprays but with far fewer insecticide applications.
Bt and spinosad products are very effective. Important, if you have a bad infestation then do not let that crop stand in the field and act as a breeding ground for the next generation. Plow it under.
Pest Report June 1, 09
COOL SOIL AND CROP GROWTH
Once again it feels to me that we got an early start with soil in good condition for planting in April and then May came with some long stretches of cool and sometimes wet weather. I am getting a number of calls that relate to this. The most frequent is poor germination of peas and beans plus some folks who rushed and put out warm weather crops before it was warm.
See last week's Pest Report for a discussion of the seed corn maggot, which will cause very spotty germination.
Don't rush out crops. Peppers, eggplant, sweet potatoes and especially crops in the cucumber family respond very poorly to cool soil. Their roots do not work well in cool soil and so they suffer nutrient problems (purple or yellowing leaves), and worse if the soil is in the low 50s, which is really cool for these crops, they will suffer physiological drought. The leaves wilt and the plant may die because the roots cannot function and get water to the plant.
ASPARGUS BEETLES [Modified from an article by Ruth Hazzard, UMass Vegetable notes, May 1, 2008]
Common asparagus beetles are active in asparagus fields. The spotted asparagus beetle tends to become active somewhat later in the spring. 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 photo on MOFGA website). Eggs are black, laid standing on end in rows along the spears, and hatch in 3-8 days. 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 fern. Eggs and larval damage makes spears unmarketable. Larval feeding damage in the ferns 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.
Life cycle: Beetles feed as soon as they become active, and begin laying eggs after several days of feeding. Eggs hatch in 3 to 8 days depending on temperature. Larvae feed for 10 to 14 days and if in large numbers can
defoliate the plant. They molt four times, then crawl into the soil to form chambers in which they spin cocoons and pupate. After 5 to 10 days, new adults emerge. There are probably two generations in this part of New
Scouting: At this time in the season, look for adult beetles, for feeding damage and for eggs laid on spears.
Cultural and biological controls. This time of year you can greatly reduce the population by harvesting ALL of the ready spears every day. Do not let spears that have gotten too big to develop. Pick the field clean to reduce
the number of stems where eggs will survive long enough to hatch and grow up into summer-generation beetles. If you harvest ALL of the spears right to the ground during the harvest period you will starve many of the beetles,
give them no site to lay eggs, and fewer will make it to the time you stop harvesting and let the fronds grow. In the fall remove all of the crop residue and other refuse nearby that may provide shelter for adults over winter, by disking lightly or burn 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.
There are several beneficial insects that attack the asparagus beetle, including a tiny parasitic wasp (Tetrastichus asparagi) that attacks the egg stage. It kills eggs by feeding on them and by laying its own eggs, which hatch and grow inside the beetle eggs. Providing a nearby nectar source such as umbelliferous flowers for the wasps may increase their chances of survival, but may not be sufficient to prevent economic damage. Chemcial control. Entrust may be used on fronds after harvest, but asparagus is not on the EPA Entrust label for treating spears. Treat ferns if 50 to 75% are infested. Organic options on spears include Surround WP as a repellent, Pyganic EC5.0, or products containing capsaicin.
References: Handbook of Vegetable Pests by John Capinera; 2008-2009 New England Vegetable Management Guide; Eric Sideman, MOFGA; Brian Caldwell, Cornell Universtiy.
The garden springtail is a wingless insect that hops like a flea beetle and eats small holes in leaves of young seedlings like a flea beetle, but is not related to, nor does it look like a flea beetle. The springtails are in an
order of insects all there own. They are tiny, plump and have a taillike appendage that they use to hurtle themselves into the air. They live in moist environments that are high in organic matter. There are many species of springtails, most of them are harmless and live on the forest floor. But the garden springtail does some harm. Young seedlings of beets, spinach, beans, onions and some others are hosts and if the population is large enough the seedling is set back by the number of holes drilled into its leaves. In most situations the seedlings out grow the pest and little harm
is done. Usually, the environment changes quickly in the spring and it becomes too dry for springtails. Anything you can do to make it less humid earlier will help, e.g., reduce surface residue, control weeds, wide crop
COLORADO POTATO BEETLE
Colorado potato beetles (CPB) adults are just starting to show up in potato and eggplant crops. 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 with the next hot spell.
Scouting and Thresholds
Walk your fields NOW 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), based on a count of 50 plants or stalks.
Controls are needed on eggplants when there are 2 small or 1 large larvae per plant (if plants are less than six inches) and 4 small larvae or 2 large per plant (if plants are more than six inches).
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. In potato, adult damage in rotated fields 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 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.
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 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
(online at 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), larvae (12-spotted ladybeetle, spined soldier bug, ground beetles), and eggs.
Organic controls. 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. NOTE: There is no longer a registered product for agricultural use in organic crops in the US that contains Bt tenebrionis as the active ingredient. 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.
(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)
Pest Report - May 19, 2009
This is the first Pest Report for the 2009 growing season. The Pest Report is sent out every week or two during the heart of the season and highlights problems happening now or likely to show up soon. I hear about problems from growers all around the region so please help out and let me know if something big or unusual is happening.
I write much, and much of what is in the Pest Report is reprinted from newsletters by crop advisors around the region. The ones I use the most are from the University of Vermont (Vern Grubinger), University of Massachusetts (Ruth Hazzard), and the University of New Hampshire (Becky Grube). As you can guess, using material from there often gives us a bit of time to prepare because many pests move into Maine from the south and west during the season, i.e., do not spend the winter here. Also, this year I will be picking out some of my own pieces from previous Pest Reports because usually the warning is the same every year.
The Pest Report pieces include a description of the pest, the biology of the pest, a description of the damage, and some suggested management practices allowed under organic standards.
The frost last night reminded me of a recommendation that I often make and that is to plant your garden based on the calendar for sure, but on top of that pay attention to the immediate weather. Even if the calendar says the soil should be warm do not put seeds out that require warm soil to germinate if the weatherman is predicting days of cold weather.
Peas, beans, corn, potato sprouts and even cucurbits in the greenhouse are attacked by the larvae of this fly named the seedcorn maggot. They are yellow-white maggots about a quarter of an inch long and sharply pointed at the head end. The symptom is usually that you see no germination, and when you dig around you may find nothing left or may find the maggots burrowing into the seed. Sometimes the seed germinates but only a weak or partially eaten plant is seen. The injury is most likely to occur in cold wet seasons where the germination is slow, and also in soil high in organic matter.
The attack is early in the spring because the critter spends the winter as pupae in the soil, or maybe free maggots in manure or unfinished compost. The adult is a grayish brown fly only about a third of an inch long. It emerges in early spring and deposits eggs in rich soil and even compost piles usually near seeds and seedlings. Exposed peat or potting soil mix of transplants can also serve as attractive sites for females looking for a place to lay eggs. There are a few generations each season.
The best method of dealing with this critter is to do everything you can to encourage quick germination and rapid growth. In the cold, wet soils the seeds are just sitting ducks. Shallow planting helps when conditions are poor. Best yet, wait for things to warm up and dry out
Wireworms (Reprinted from Becky Grube's Newsletter)
I have gotten quite a few questions about problems with wireworms recently. Wireworms damage root and tuber crops such as potatoes and carrots by tunneling, causing unsightly holes as well as providing an entry point for pathogens. Young seedlings with small root systems can be weakened or Life of the Wireworm. Wireworms are the larvae of click beetles (family Elateridae). There are many species of wireworm. The larvae have slender, hard, ¾ -1 inch long bodies that range from tan to orange to brown in color. The larvae pupate in the spring, and the adult beetles emerge and are active in the summer. The adult beetles are not typically pests. Female click beetles lay eggs during May and June. They lay eggs in the soil, primarily in weedy or grassy fields. The eggs hatch in 3-4 weeks, and the larvae then look for food. The larvae can live for several years, depending on the species, availability of food, temperature, and soil moisture. Because eggs are typically laid in grassy fields, wireworm problems are usually most severe in fields that were recently sod. However, because the larvae can live for many years, problems can persist in fields that have not been sod for some time. And grassy cover crops can attract the adults for egg laying. Wireworms are often more prevalent in moist areas of fields, and in areas with high organic matter.
What they Eat. Wireworms are omnivores. They feed on the roots of grasses or weeds and on other soil insects. It is hard to starve wireworms out of a particular area, because of their diverse diet. Crops that tend to increase wireworm populations include potato, carrot, sweetpotato, small grains (wheat, barley), onion, beet, and clovers. A clean (non-weedy) alfalfa crop can reduce populations. This may be in part because of alfalfa's deep root system reduces soil moisture, making the environment less favorable for the larvae.
Minimizing Damage. Rotation into alfalfa or crops that are not preferred can reduce wireworm populations. Avoid planting highly susceptible crops such as potato and carrots into sites with a high potential for damage, such as fields previously planted to grass sod, pasture or small grains, or fields with a prior history of wireworms. The edges of fields (near sod) can also be a problem, because the larvae can move through the soil in search of food. Baits can be used to determine wireworm pressure prior to planting a susceptible crop. This can be done by placing carrots or potatoes in a softball-sized hole about 4-6” deep, covering with loose soil, and then covering the area with a piece of black plastic to warm the soil. Wait 4-7 days, and dig up the bait to check for the presence of wireworms before planting. On small scale plantings this baiting sytem can be used to reduce numbers in gardens. Another version of this method involves burying a fist-sized clump of corn, wheat, or rolled oats. It may also help to harvest crops as soon as possible. Some reports indicate that the wireworms seek out the moisture in potato tubers if soil conditions become dry, and wireworm damage increases over time in potato crops left in the ground.
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. [Different species of flea beetles feed on the tomato family of crops.] 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 Œshot-holes¹. 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. Occasionally in tender greens such as arugula, tarnished plant bug feeding may be confused with flea beetle feeding. In addition to the shot holes from flea beetles, there may also distorted leaves that are typical of TPB feeding, which injures leaf tissue when leaves first emerge.
To reduce and delay flea beetle invasion of spring crops, move them as far away from the fields that were used for fall Brassica crops as possible. Remember when you choose rotation fields that the species of flea beetle on Brassicas are different from those on the tomato family. Beetles overwinter in field borders near last year¹s crop. Planting the same crop close by to where it was last year ensures a high population in the spring.
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, 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 the Pyganic right through the floating row covers and knock down any flea beetles that may have gotten inside.