Cucumber Beetles

Injury

Two species of cucumber beetles, the spotted cucumber beetle and the striped cucumber beetle, attack cucumber, cantaloupe, gourds, muskmelon, squash, and pumpkin. Spotted cucumber beetles also attack asparagus, beets, cabbage, corn, eggplant, beans, peas, potato, tomato, and a wide variety of flowers. These beetles cause similar foliage damage, but the injury caused by the striped cucumber beetle is usually more severe. Adults feed on stems and leaves as soon as plants emerge from the soil attack flowers and even bore into the fruit rinds later in the season. Cucumber beetles transmit a serious plant disease called bacterial wilt (Erwinia tracheiphila), which clogs the water conducting tissues in the plants and may kill entire vines by mid-summer. All cucurbits except watermelons are susceptible to bacterial wilt. Cucumber beetle larvae feed on underground portions of the plant, boring into the roots and stems, although this damage is usually not serious.

Description

Both beetles are about the same size and shape. The striped cucumber beetle, Aclymma vittatum, is 1/5-inch long with a black head yellow thorax and wing covers, and three distinct longitudinal stripes on the wing covers when folded. The spotted cucumber beetle, Diabrotica undecimpunctata howardi, is a yellowish-green beetle about 1/4-inch long with a black head and black legs and 12 distinct black spots on the wing covers. The larvae of both cucumber beetles are similar-slender white grubs with a brown head capsule.

The spotted and striped cucumber beetles hibernate as adults in dense grass, at the base of weeds, or under plant residue, emerging in early May when temperatures reach 60°F or higher. Adults of the spotted cucumber beetle appear in early spring, followed by adults of the striped cucumber beetles. Beetles feed on the pollen and leaves of many plants until cucurbits are up, then migrate to the seedling cucurbits and feed for an extended period of time, depositing yellowish orange eggs in the soil near the host plant. The eggs hatch in about 1 week; the larvae work their way down to the roots to feed and soon pupate in the soil. After pupating for about 7–10 days, new adults emerge in mid-summer to produce another full generation of beetles.

Management of Cucumber Beetles

1. It is important to protect seedlings and small plants from beetle feeding, as they are more susceptible to bacterial wilt.
2. Crop production practices that promote strong root growth and a vigorous crop will make the plants more tolerant to cucumber beetle feeding. Fertilize properly so plants grow rapidly early in the season.
3. Early beetle feeding can be avoided by placing row covers or insect netting over the seedlings. Remove row covers or insect netting when plants flower to allow for insect pollination. If you choose to grow parthenocarpic (varieties that do not require insect pollination for fruit set), row covers can remain through flowering and fruiting. Some seed catalogs indicate which varieties are parthenocarpic.
4. For information on insecticides see Vegetable Insect Control Recommendations for Home Gardens, FS1123. Treat early to prevent beetles from feeding on the seedlings and thus reduce the spread of bacterial wilt.

Avoid overuse of insecticides as you may kill beneficial insects. Read and follow all pesticide label directions, restrictions, and pre-cautionary statements before using any pesticide. Remember that insecticides may be harmful to bees foraging in the area. Pesticide applications late in the day or at night will avoid actively foraging bees. Days to harvest after last application varies depending on crop and pesticide—refer to the label for appropriate time intervals.

This is based on the original work of:
Gerald Ghidiu, Extension Specialist Emeritus in Vegetable Entomology, Retired
Kristian Holmstrom, Vegetable IPM, Research Project Coordinator, Retired
Joseph Ingerson-Mahar, Vegetable IPM, Senior Program Coordinator, Retired.