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MOFGA's Pest Report - June 29, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

The season still is a tough one for many because of continued wet weather and wide fluctuations in temperature alternating from cool nights to heat waves. Growers with well drained soils are sure doing better than growers with clay or high water tables. Late blight is still popping up, but staying well south of us. I am worried because the weather has been right for it to spread north, but it hasn't yet. Keep your eyes open for a "Pest Alert" rather than the usual "Pest Report" in the subject lines of your emails from me. Spotted Wing Drosophila has been reported already, but it too is well south of us at this time.

In this issue of the Pest Report I will cover:

  • Asiatic Garden Beetle
  • Potato Leaf Hopper
  • Squash Vine Borer
  • Tomato Fruit Worm
  • Caterpillars in Brassica Crops

By the way, a week or two ago my brother was out walking and a farmer passing by in his truck stopped and rolled down the window and said, "your brother sure is a pessimist". I have that reputation in the MOFGA office too. Still, some find the Pest Report useful and stay happy. I am going to go out and enjoy this sunny day, the first in five.

Asiatic garden beetle. Photo by Eric Sideman.

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

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

Potato leafhopper damage. Photo by Eric Sideman.

Potato Leafhopper (Empoasca fabae) - I have seen some potato leaf hopper (PLH) already, so this is the time to keep an eye out for them. They could appear at your place at anytime, and remember, once you see severe damage from them it is too late to do anything. You have to find the insect and manage it before the plant symptoms catch your eyes.

They primarily feed on beans, potatoes, eggplants, strawberries and alfalfa. The 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, and is frequently mistaken as such. The leaves first get pale, then yellow and then brown from the edges. Then the plant dies. The symptoms are called hopper burn. It all happens very quickly.

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 even 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 of them, you are in trouble. Researchers have developed a threshold before treatment is recommended. Thresholds vary but here is one that is typical: Treat potatoes if 5 adults or 15 large larvae are found on 50 leaves.

Crop rotation does nothing for you since they are coming from far away. Covering your crops with a row cover would work, but these crops are not the type that are usually covered. Effective insecticides are limited. The only material that I have seen work that is allowed in organic production is pyrethrum, so Pyganic is the recommendation that I make. However, it does not work as well as a pyrethrum with PBO. BUT PBO is not permitted in organic production. If you market crops as organic, be sure to use an approved brand of pyrethrum, such as Pyganic 5%. Use the most concentrated mix allowed. Spray late in the day or evening, get good coverage including the undersides of the leaves, and don't wait until it is too late.

Squash vine borers. Photo by Jeff Hahn, University of Minnesota Cooperative Extension.

Squash Vine Borer - Squash vine borers are showing up in traps in NH already, and I am sure that southern Maine is next. Many vine crops are in bloom, and the row covers have been taken off to allow the bees access, and that means the borer now has access too. Care should be taken during bloom to avoid using insecticides when the bees are active.

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

Growers should scout their pumpkin and squash fields weekly for squash vine borer from late June through early August. Examine the base of vines for eggs. The squash vine borer can be killed with an insecticide and the recommendation would be spinosad (Entrust, Monterey Garden Spray), but appropriate timing is crucial. The insecticide is most effective when applied to young larvae before they bore into the stem. Once they are in the stem the insecticide will be useless. If you see the moths flying or find eggs, then two insecticide sprays, ideally applied to the base of the plants and timed five to seven days apart, will control newly hatching larvae before they are able to bore into the stem. Again, the timing is crucial and there is no point in spraying before you find evidence or after the larvae bore into the stem.

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

Some growers monitor for the moths using Scentry Heliothis pheromone traps from early June through early August. If more than 5 moths per week are captured, then they make 2 to 4 weekly applications of pesticides. Timing is very important, so this is not recommended for the casual gardener. - Source material from New England Vegetable Management Guide; Handbook of Vegetable Pests, A Capinera; ATTRA, UMass Vegetable Newsletter and URI Extension Fact Sheet.

Tomato fruitworm. Photo from North Carolina State University Cooperative Extension.

Tomato Fruitworm - I have seen in our own high tunnel of tomatoes, and have received reports from other growers, a caterpillar feeding on tomatoes. It is eating large holes in the side of the fruit. The numbers in each tunnel are small, but loosing even a single beautiful red tomato is awful. I think this is the tomato fruitworm, but it may be a related species. If anyone has a similar problem, please try to get me a sample. I took pictures, but my expert entomologist says he needs a specimen to get a sound identification. I put mine into the chicken pen and I cannot seem to find them anymore.

The tomato fruitworm is actually the same critter known as the corn earworm when it feeds on the tips of corn. It does not over winter here in the north, but every year, to a greater or lesser extent, they migrate up from southern regions. The preferred food is corn, but if none is available other items will do, e.g., tomatoes, peppers, lettuce, cotton and more. I rarely see them, except on corn.

The moth flies at night and typically lays eggs on the silk of corn. On tomatoes the eggs are laid on leaves near the flower or young fruit. The eggs hatch in 2-5 days. The caterpillar crawls down the silk channel to the kernels on corn, and to the fruit on tomato. They are pretty voracious feeders and can do a lot of damage. Rarely do you find two of them on the same fruit because they eat each other. The young caterpillar are pale, and the grown caterpillars are very variable in color, from green to brown to striped with spots. Bt will kill them, but I have not found enough to warrant spraying.

Above: Diamondback moth larva. Photo by Eric Sideman.
Above: Imported cabbageworm. Photo by Eric Sideman.
Above: Cabbage loopers at various stages. Photo from North Carolina State University Cooperative Extension.

Caterpillars in Brassica Crops - There are three common caterpillars that feed on our broccoli family crops. Keep an eye out for them. The imported cabbageworm butterflies are flying now.

Quick ID Cues:

  • Diamondback moth caterpillar: Green, very wiggly when poked, pointed on both ends, not fuzzy, only grows to about 1/2 inch. You may find white silken cocoons. They eat wholes in the leaves. There are many generations in a single season, even though they do not overwinter here.
  • Imported cabbageworm: gray-green, slightly fuzzy, and sluggish. Grows to >1 inch and favors the center of the head as it gets larger. Leaves wet green frass (droppings). Eggs single, light green or yellow. They eat large chunks out of leaves. The adults are those white butterflies you commonly see flying around your broccoli.
  • Cabbage looper: light green, smooth, loops up like an inch worm as it moves. Eats big holes in leaves.

Scout undersides of leaves to look for fresh damage, and get control of the caterpillars when they are small and damage is slight. Check heading crops as soon as heads start to form. Greens should be scouted at all growth stages.

For organic growers both Bt and Spinosad are very effective (Bt products are a lot cheaper), but remember to only spray after scouting and assessing damage. The pest has to be there to be killed, i.e., neither material has long efficacy after spraying. Destroy crop after harvest so it does not act as a harbor for the pests all season.

For more information, contact:

Eric Sideman
Organic Crops Specialist
Maine Organic Farmers and Gardeners Association
Phone: 603-269-6201

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