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

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Pest Report- June 14, 2009

HORSEHAIR WORMS

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.

TOMATO SPOTS

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.

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