By Whitney Cranshaw, Colorado State University Cooperative Extension, Entomology
One of the earliest garden visitors are flea beetles. Aptly named, they are among the smallest of beetles and readily jump, flea-like, when disturbed. As a result, the insects sometimes elude the gardener but the damage they cause to plants is distinctive. Flea beetles chew small pits into leaves, giving plants the appearance that they may have been blasted with fine shot. Such "shothole" feeding is most common on cabbage family plants due to the most notorious of the Colorado flea beetle bunch, the western cabbage flea beetle. However, other flea beetles are common on tomatoes, potatoes, eggplant, horseradish, and beans.
Flea beetles are most damaging to plants that are in seedling stages or struggling to become established after transplanting. In extreme cases plants may be so badly chewed that they are killed or greatly retarded.
However, established plants that are actively putting on new growth are little affected by flea beetles, fully compensating for the injury they produce. Thus the key to avoiding problems can be to provide cultural conditions that allow for vigorous plant growth and rapid establishment in the garden. Seeded crops that chronically are badly damaged, such as broccoli, can usually outgrow flea beetle wounding when grown as transplants.
Trap cropping can sometimes be used to allow seedling crops to get over the hump and past the point where flea beetles can seriously affect the crop. For example, radish and daikon are extremely favored by the cabbage flea beetle. Yet these fast growing plants are vigorous enough to well tolerate the insect - although there may be many holes in the leaves. By planting these near a more susceptible crop, such as seedling mustard or broccoli, a large number of the flea beetles will be diverted to the radish, relieving the main crops.
Flea beetle control with insecticides often produces disappointing results as these insects are very migratory and new ones are continuously visiting the garden. Sevin and permethrin are the best treatments, but can provide control only for a few days. Gardeners may also try repellents. Diatomaceous earth, horticultural oils and some neem-based insecticides have proved to be the most effective repellents in CSU trials.
Photos: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010