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MOFGA's Pest Report - May 15, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Spring Woes: This is a very good year to point out the importance of consideration of soil type when buying your farm or garden. I often say you can deal with anything, and dealing is what is happening now for those of us who did not think about it much back then and now have poorly drained soil. Two related problems that I discussed in the last issue of the Pest Report are very common this year. I have never had as many calls about onion maggot and seed corn maggot as I received last week, and spinach germination and survival is at an all time low. Spinach is going down (or not coming up) due to damping off and/or the seed corn maggot. See last week's issue for details. If waiting for dry, warm soil seems futile, you may want to spend some money on products. There have been some fair-good reports of successful avoidance of damping off using a biological control product made from Trichoderma, such as, RootShield® Granules or RootShield® Home & GardenBiological Fungicide (BioWorks, Inc.), and SoilGard® 12 G Microbial Fungicide (Certis). Let's hope for some dry weather as that would be best.

Above - Adult common asparagus beetles.
Above - Asparagus beetle eggs.
Above - Asparagus beetle larvae.

Asparagus:

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 for my tenure, but I stuck it out. 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. The early hot spell this year moved everything, including asparagus, ahead by weeks. It made some growers in-the-know uneasy as spears pushed out of the ground, only to face the a string of cold nights. There is still a good chance of frost though you would not believe it since it was over 80 yesterday! 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 are here. 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 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. 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. Some people call them "worms". 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 severe 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. 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.
  • 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.

Cultural controls: During harvest, you can greatly reduce the population by harvesting ALL of the spears every harvest. 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. Treating infested fronds is important. Organic options include Entrust. Surround WP may work as a repellent. Thanks to for information: -R. Hazzard (U. Mass Vegetable Notes & The New England Vegetable Management Guide), and Brian Caldwell, Cornell University.


Above - Adult Mexican bean beetle.
Above - Mexican bean beetle larva.

Mexican Bean Beetle: Plan Ahead For Biological Control (Reprinted and modified from Mass. Veg. Notes, written by Ruth Hazzard and A. Brown)

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; address; NJDA, Phillip Alampi Insect Lab, State Police Drive, W. Tren- ton, 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., NH., www.green-methods.com 603-942-8925; IPM Laboratories, NY 315-497-2063; ARBICO, 800 -827-2847 (AZ), http://www.arbico.com/; Network (TN), 615-370-4301, http://www.biconet.com/.

If you would like assistance in using these biocontrols in your bean crops please call the UMass Extension Vegetable Pro- gram 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.


Above - Late blight in tubers.
Above - Fusarium dry rot.
Above - Ring rot.
 
 Above - Black scurf.

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:

  • Late Blight - Of course this is the big one. Look at the picture on the web version if you don't know what this looks like. If you are not sure, check with an expert. Besides taking down your potato crop, this is the most likely source of a community or state wide problem this year. 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 seen on seed pieces, and can result to 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 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. 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 with the tuber and the inner walls may be white, tan or even may be rarely 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:

I have had no reports of flea beetle feeding yet, but I bet that feeding on early spring plantings of brassica crops will start soon. Then numbers are likely to rise quickly as beetles move out of field borders where they spent the winter. Since row covers are by far the best management strategy, it is better to be prepared than wish you were.

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. This is good to know when planning rotations.] 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. The crop quickly becomes unmarketable. In contrast, waxy crops are most susceptible at the cotyledon and seedling stage, and then feeding is more limited to leaf margins on older plants. Usually the crop outgrows the pest so use of row covers is usually not essential on the waxy crops. 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 or delay flea beetle invasion of spring crops, move them as far away from the fields that were used for fall Brassica crops as possible. Beetles overwinter in field borders near last year’s crop. Planting close by ensures a high population early in the spring.

 
 Flea beetle trying to get through Proteknet.

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.

This may be the year to try out the new product called Proteknet. It is distributed by Dubois Agrinovation, out of Canada.

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

Fedco is selling it this year in smaller rolls. It is, as the name implies, a fine net rather than a spunbound covering. It is said to have a 5-year or more life. [See the web version of this Pest Report for a picture.]

Spinosad (Entrust is organic formulation) is proving to be effective in suppressing flea beetles and reducing damage. Pyrethrum (Pyganic EC 5) showed poor to moderate efficacy in trials, and has a short residual period. But, 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. (Thanks to the UMass Vegetable Notes for much of the information above).


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