Flea Beetles on Eggplant

Flea beetles are small insects that feed on the leaves of plants, resulting in stunting and yield reductions. Eggplant is particularly susceptible to flea beetle feeding, and resulting yield reductions of over 60% have been reported.^1,2 Several species of flea beetles can be found on eggplants, including the eggplant flea beetle (Epitrix fuscula), the potato flea beetle (Epitrix cucumeris), the tobacco flea beetle (Epitrix hirtipennis), and the pale-striped flea beetle (Systena blanda), although the eggplant flea beetle is the dominant species on eggplant in many locations in the U.S.^2,3 These species of flea beetles may also be found on potato, tobacco, tomato, and Solanaceous weeds, such as nettle, nightshade, and jimsonweed.²

Young plants are particularly susceptible to flea beetle feeding, which may cause plant death in some cases. Older, larger plants (past the four- to five-leaf stage) are better able to withstand feeding damage.^3,4,5 A study of flea beetles on eggplant in Virginia showed that fruit yields from plants with no beetle feeding damage were significantly higher than yields on plants with more than 21% defoliation from feeding, and yields decreased as the percent defoliation increased.²

Flea beetles overwinter as adults in plant debris, leaf litter, hedgerows, windbreaks, and wooded areas. The adult beetles emerge (become active) in the spring when temperatures reach 50 °F, and begin feeding on eggplant leaves. The adults are most active on warm, calm, dry, sunny days^.1,3,4,5 In the Virginia study, flea beetles were detected on eggplant seedlings immediately following transplanting in late May, and the beetle population increased over the summer, peaking in early August.² Shortly after becoming active, the adult female beetles lay eggs in the soil. Larvae hatch and begin feeding on plant roots of several vegetable and ornamental crop species, but root feeding usually does not greatly affect plant growth. The larvae feed for two to three weeks before they pupate, and adults emerge from the soil in an additional two to three weeks. There can be one to several generations of flea beetles, depending on the location and conditions^.1,4,5

Adult flea beetles can overwinter in crop debris, so remove or cultivate plant debris at the end of the season to help reduce overwintering populations. Light tillage of the soil in the fall and spring and covering the soil with black plastic a month before planting in the spring can also help reduce the in-field flea beetle population.¹ Transplanting larger seedlings that can better withstand beetle feeding and planting in the later part of the planting window to avoid the overwintered beetle generation and help promote rapid, vigorous seedling growth can help plants better out-grow feeding injury and minimize the impact of flea beetle damage.^1,3,4,5

Row covers can be used to help exclude flea beetles from young seedlings, but hoops should be used with eggplant to keep the row covers from resting directly on the plants. Kaolin clay can also be sprayed on plants to serve as a particle barrier, which can help inhibit flea beetles and reduce feeding damage. However, studies of the effectiveness of kaolin clay applications have shown mixed results, and the clay needs to be reapplied after rainfall because it is easily washed off of plant surfaces.^1,5 Between-row cultivation periodically during the growing season can help disrupt the larval and pupal flea beetle stages developing in the soil, later helping to reduce the number of adult beetles in the field.⁴

The presence of flea beetles can be monitored by placing white or yellow sticky traps within and at the edges of eggplant fields. Young plants should be scouted every one or two days to look for the presence of adult beetles and for feeding damage on leaves.^3,4,5 The action threshold for eggplant seedlings less than three inches tall is more than two beetles per plant. On plants three to six inches tall, the threshold is four beetles per plant, and for plants more than six inches tall, the action threshold is an average of eight beetles per plant.^3,5

If flea beetle populations reach the action threshold, insecticides can be applied to help protect yield potential. Several insecticide products are labeled for use in the control of flea beetles on eggplant, including beta-cyfluthrin, bifenthrin, carbaryl, esfenvalerate, imidacloprid, lambda-cyhalothrin, permethrin, pyrethrins, pyrethrum, Spinosad, thiamethoxam, and others.^5,6 Be aware of the pre-harvest interval (PHI) for use on eggplant indicated on the product label, and follow all label recommendations and restrictions.5 Insecticide applications may not be needed later in the season as plants are better able to withstand flea beetle damage and beetle population levels begin to decline.