Beating the Bugs
by VCE Agent Kirsten Conrad
The information here was originally published in a monthly column on pest control in Between the Rows – A Guide to Vegetable Gardening published by VCE in collaboration with MGNV.
Don’t miss Kirsten’s in depth online class:
What’s Eating My [Cucumbers, Tomatoes, Eggplant, Beans, Squash]? :
Insect Pest Management for the Vegetable Garden
Pests of Tomatoes, and Peppers
Ah, the joys of harvesting fresh peppers and tomatoes that you have grown yourself! It’s June and your warm season crops should be coming into their own. In particular the members of the Solanaceae family — the peppers, tomatoes, and eggplants — are just loving the heat. A few insect pests love them as much as we do. By far the most serious of these are the flea beetles. These tiny, quick moving, dark blue, black, brown, or striped beetles feed on eggplants, pepper, cole crops, beets, spinach, mustard, and radishes. Also significant in Virginia are Colorado potato beetles, whiteflies, and grasshoppers.
Flea beetles emerge from the soil in early spring to chew holes in the leaves, mate, and lay eggs near the soil line. Its larvae feed on roots and pupate into adults in 2-3 weeks. There are multiple generations per year.
Control these with crop rotation, fall tilling of debris into the soil, and using a row cover of floating fabric. Once infested, use diatomaceous earth or pyrethrin sprays for heavy infestations. Azadirachtin or kaolin clay provide good control. Always avoid applying insecticides to flowering plants and always read the label.
Whiteflies, in addition to being tomato pests, are also a serious kale and collards pest. Related to scale, leaf hopper, and mealybug insects, adults are only 2 mm long and resemble small white moths. Whiteflies can vector virus diseases, and populations can build up to large numbers very quickly, which will kill plants. Immature pupal cases look like pale yellow-white scale insects on the bottom of leaves.
When buying plants inspect carefully to ensure that they are pest free. Interplanting susceptible crops with small flowering plants will provide some biological control. Control the egg and immature stages with oil (horticultural, canola, neem) sprays or with insecticidal soap. Completely saturate the underside of all leaves and repeat application in 2 weeks. Heavier infestations may require use of imidacloprid, permethrin, or pyrethrins. Be mindful of the days before harvest (pre-harvest interval) listed for every chemical control. These range from 1 to 21 days.
Although peppers both hot and sweet are remarkably easy to grow, our Virginia Tech specialists say that in addition to grasshoppers and the European corn borer, the most common pests are aphids, thrips, and stink bugs.
Thrips are tiny and hard to see. The winged adult, only 1/25 inch long, is bright yellow, and the even smaller immature thrip is wingless. They do deep damage to the leaf or flower buds, which is not evident until the buds open revealing distorted, withered, and/or brown or white dead plant tissue.
Thrips lay eggs in early summer on buds and leaves. Multiple overlapping generations of thrips can occur in Virginia on onion, bean, carrot, cabbage, cauliflower, celery, cucumber, melon, pea, squash, tomato, and turnip.
Control options are chemical control, dusting with diatomaceous earth, some predation by minute pirate bugs and lady beetles, and organic controls such as spinosad, insecticidal soap, and pyrethrins.
Tomatoes are the source of our most frequently asked vegetable insect control questions. In addition to flea beetles, aphids, thrips, and whiteflies that we covered earlier, we also need to fight off tomato’s most common pests — stink bugs, hornworms, spider mites — as well as blister beetles, tomato russet mites, cabbage looper, Colorado potato beetle, cutworms, grasshoppers, leaf-footed bugs, and fruitworms/corn earworm.
Stink Bugs are about 5/8 inch long and are shield shaped. Their eggs are barrel shaped and laid 20-70 in clusters on the bottom of leaves. Two of the most common here are the harlequin bug and the brown marmorated but green stink bugs and leaffooted bugs cause similar damage and are controlled in the same manner.
Adults and nymphs feed on plant buds and seedpods, which results in malformed buds and fruit. On okra and bean pods, the damage appears as raised spots. On tomatoes and peppers, white marks, often resembling halos, appear on the fruit
See a gallery of stink bug damage here: BMSB Damage Gallery.
Cultural control of some stink bugs can be achieved by removing weeds and wild fruit trees around gardens, and organic controls are limited to pyrethrins. Various chemical insecticides are effective only as contact sprays and provide very little residual control. Systemic insecticides are licensed for use on food crops, too, but are rendered nearly useless by their 21 day pre-harvest interval requirement
These tiny, about 1/50 of an inch, arachnids are pale in color, often with two dark spots. They are indiscriminate feeders on beans, tomatoes, and many bedding plants. Mite feeding causes the leaves to look sandblasted with lots of tiny yellow or off-white spots. Spider mites leave webbing and debris on leaves and plant stems. Heavy feeding can cause an entire leaf to yellow and eventually turn brown.
Chemical controls are not recommended because they make the spider mite problem worse by killing off beneficial mites and predators. Make sure plants are well watered and remove and compost any green weeds and clumps of grass in the winter. Predatory beneficial phytoseiid mites are available for purchase.
Two species of hornworm damage tomato plants in Virginia: the tobacco hornworm and the tomato hornworm. Both of these are large (up to 4”) and are green with diagonal lines on their sides and a horn on their rear ends. Hornworms feed on leaves and fruit and are almost always on the upper top part of the plant.
Controls include handpicking the worms and destroying any that don’t have wasp cocoons on them because these will provide biological control on future generations. Organic control is provided by Bacillus thuringiensis when hornworms are less than 1/2 inch long. Chemical control with capsaicin and oil of mustard, Beauveria bassiana, neem oil, azadirachtin, and pyrethrins must also be done when the larvae are less than 1/2 inch long.