Cucumber beetle can spread wilt

The striped cucumber beetle is a serious pest of cucurbits (cucumber, squash, pumpkin, melon and others). The adult beetles migrate from their winter hiding places in sheltered areas under plant debris to feed on stems and young leaves and lay eggs at the base of emerging plants. Later as the host plants grow, the beetles feed on plant leaves, vines, flowers, and fruits. The chewing mouthparts of the adult beetles are responsible for small shot holes in leaves, stem wounds and pitted fruit rinds. The larvae feed on stems and roots, setting the plants up for future problems such as poor water and nutrient uptake, and disease entry.

The beetle is capable of spreading bacterial wilt and squash mosaic diseases. The bacteria causing wilt lives in beetles that survive the winter in protected areas. The bacterial disease is spread through beetle-feeding and droppings. In the early stages of bacterial wilt, gardeners may notice their plants wilting, one leaf at a time. Eventually, the whole plant wilts. Symptoms usually show up within two weeks of striped cucumber beetle feeding.

The striped cucumber beetle is about 1/4 inch long, has three black stripes down its back (on a yellow background), and has a yellow section behind its black head. The eggs are yellowish-orange. The full-grown larvae are about 3/8 of an inch long, slender, light-colored and dark at both ends.

It is important to inspect newly emerged or transplanted seedlings frequently, because the beetles can be present early in the season. Highly motivated people may consider handpicking the beetles off the plants in the cool of the morning, when the beetles are slow to fly away. Transplanted seedlings and emerging plants can be protected from striped cucumber beetles by using floating row covers. Be sure to remove the covers to allow for flower pollination. If the plants are in a windy location, consider suspending the covers with wire hoops to prevent leaf damage. Removal of weeds, such as goldenrod and aster, near cucurbits may help reduce the numbers of beetles. Getting rid of plant debris in the fall will limit potential winter hiding spots.

If you choose to use insecticides, there are several organic and conventional sprays and dusts that are available for protecting plants from these pests. Contact your local Cooperative Extension Office or the Pest Management Office for specific options.

Some allies in your battle against the striped cucumber beetle include beneficial insects such as soldier beetles, tachinid flies, braconid wasps (harmless to people) and nematodes.

Clay Kirby is an insect diagnostician in the Pest Management Office of the Maine Cooperative Extension Service in Orono. He can be reached at (800) 287-0279.