The cucumber beetle is an oblong greenish-yellow beetle with black spots or stripes on its wing covers. The cucumber beetle is about ¼ inch long.
Cucumber beetles feed mainly on members of the cucurbit family—cucumbers, melons, and squashes—and also asparagus, early beans, corn, eggplant, peas, potatoes, and tomatoes. They attack seedlings feeding on young shoots and leaves. They also attack older plants eating holes in leaves and fruit.
Cucumber beetles carry the bacillus Erwinia tracheiphila which causes bacterial wilt in plants. And, cucumber beetles can spread mosaic virus by feeding on an infected plant then feeding on a healthy plant. There is no cure for mosaic virus or bacterial wilt.
Overwintering adult beetles emerge from garden debris or weeds in the spring and lay eggs in the soil close to plants. The eggs hatch and larvae feed in the roots and crowns of plants for 2 to 4 weeks then pupate. The larva of the cucumber beetle is called the southern corn rootworm.
There are two to three generations of cucumber beetles each year.
Target Plants: Larvae feed on roots of corn, beans and other legumes and many vegetables especially cucurbits (cucumbers, melons, and squash). Adults feed on beans, corn, peas, cucumbers, melons, squashes, and the flower petals of many plants.
Feeding Habits and Damage: Feeding cucumber beetles leave large, ragged, roughly oval holes in leaves and flowers. As they feed, the beetles can spread bacterial wilt and mosaic virus. Larvae feed on roots of corn often killing young plants; older plants are weakened and may die.
Organic Controls: A barrier of agricultural fleece will keep beetles from flying in to lay eggs near the plants. Cucumber peelings or squash cut in half and coated with rotenone can be used as traps for beetles. Diatomaceous earth can be spread around the base of plants as a barrier to egg laying; leaves can be dusted at night to control adults. Parasitic nematodes can be applied to soil weekly to control larvae. Large infestations of adults can be controlled with pyrethrum or rotenone sprays.
Organic Control Calendar: Here is what you can do seasonally to control cucumber beetles:
- Before planting: Remove crop residue from the garden. Plant an extra early squash-family crop as a trap crop then destroy the beetles attracted to it.
- At planting time: Plant crops late to avoid the first generation of beetle feeding and egg laying. Cover seedlings or transplants with floating row covers and hand-pollinate covered squash crops or remove the cover when plants flower. Pile deep straw mulch around plants to discourage the movement of beetles between plants. Place yellow sticky traps in the garden.
- While crops develop: Spray kaolin clay on undersides of leaves to deter beetles. Handpick beetles as often as possible; crush them or drop them in soapy water. Use a handheld vacuum to collect beetles, then dump them in soapy water. Grow vine crops on trellises which make spotting beetles easier. Drench the soil with Heterorhabditis nematodes to kill larvae. Spray pyrethrin to kill beetles.
- After harvest: Remove all crop debris from the garden after harvest to destroy overwintering spots for beetles. Turn the soil just before frost to expose dormant beetles to killing cold.
Natural Predators: Insect predators include beneficial nematodes, soldier beetles, and braconid, chalcid, and trichogramma wasps (wasps parasitize the eggs). Animal predators include Baltimore orioles, bluebirds, brown thrashers, chickadees, juncos, phoebes, purple finches, sparrows, towhees, and warblers.
Scientific Name: Diabrotica undecimpunctata howardi (spotted cucumber beetle); Acalymma vittatum (striped cucumber beetle).