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 MOFGA's 2009 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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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.

(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)


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.

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