||Adult flea beetles (Coleoptera) on radish (Raphanus)
Small round holes in leaves and insects that jump like fleas are two signs that a plant is infested with flea beetles. These shiny oval beetles may be black, brown, bronze, or striped and are only 1/10 inch long. They quickly leap out of sight when disturbed. There are several species of flea beetle and while some feed on only a few closely related plants, others feed on a wide variety of crop plants. Many vegetable crops are affected including tomatoes, potatoes, cole crops (cabbage family), turnips, radishes, corn, beans, and beets. Flea beetles are especially attracted to eggplants and plants may be almost totally defoliated. Flea beetles may also be vectors for transmission of disease such as bacterial wilt in corn.
Symptoms and Diagnosis
Since flea beetles are so small and active, it is easy to miss them. Watch for a sudden burst of jumping black spots among the leaves. Disturbing the foliage of the affected plant or of nearby plants may cause them to jump again. Commonly found in newly planted vegetable gardens, flea beetles are most harmful to seedlings. Larger plants are usually able to withstand damage. A light infestation of flea beetles is characterized by tiny round pits or holes in leaves, creating a shot hole pattern. Heavier infestations may cause bleached or pitted areas, ragged holes, or even total loss of leaves resulting in wilted or stunted plants. Although the larvae feed on roots of the same plants, they usually do not cause injury. Larval tunneling may sometimes cause scarring on potato tubers.
Adults overwinter in the soil and plant debris, emerging in spring to feed. They lay eggs in the soil and die by early July. The legless white or gray larvae hatch in a week and eat plant roots for 2–3 weeks. The larvae pupate in the soil and mature into adults in 2–3 weeks. There may be more than one generation a year.
Integrated Pest Management Strategies
1. Transplant large sturdy seedlings. Large transplants will be most able to tolerate damage. Monitor plants closely so that pests may be controlled before damage is severe. When planting seeds directly into the garden, sow extra seeds to allow for loss. Growing susceptible plants interspersed with less susceptible plants may help.
2. Use row covers on susceptible plants, especially seedlings and eggplant.
3. Avoid flea beetles.Plant susceptible crops as late as possible to avoid flea beetles, which are most active in early spring.
4. Till the soil in fall or early spring. This helps to remove the weeds and crop debris that provide a habitat for overwintering adults. During the growing season, cultivate soil to disrupt larval habitat and control weeds to prevent flea beetles from jumping in from adjacent weedy areas.
5. Use white sticky traps to monitor and trap flea beetles.
6. Use insecticides. Effective products include insecticidal soaps, pyrethrins, sabadilla, Neem (when registered for food crops), diatomaceous earth, or permethrin (Eight). Planting trap crops such as radish and then spraying those plants can help reduce the crop’s exposure to insecticide. Predatory nematodes may be used as a soil drench to control larvae.
Strategies 1, 2, 3, 4, and 5 are strictly organic approaches. For an organic approach to Strategy 6, consult the Organic Materials Review Institute (OMRI™) for appropriate insecticidal soap, pyrethrin, and Neem products.