Cucumber beetles attack cucurbits: cucumbers, squash, melons.
Cucumber beetle adults are yellowish and about 1/4-inch long. There are two types of cucumber beetles, striped and spotted, in Illinois. Striped cucumber beetles are more common in Illinois than spotted cucumber beetles.
- The striped (Acalymma vittatum) have three distinct black stripes that run the entire length of their elytra.
- The spotted (Diabrotica undecimpunctata howardi) have 12 black spots on their elytra.
Cucumber Beetle Habit
Cucumber beetles overwinter as adults in sheltered places, but only the striped cucumber beetle overwinters in large numbers in Illinois. The spotted cucumber beetle migrates in from the south. In spring, they feed on nearby vegetation of fields and woodlots before suddenly appearing in large numbers on vine or bean crops. Adult beetles lay eggs in the soil at the base of the plant on which they are feeding. The larvae hatch and feed on roots for 2-4 weeks before pupating and emerging as adults. There are several generations per year.
Cucumber Beetle Damage
Adult cucumber beetles eat holes in leaves and cause window-panning of leaves of cucumber, squash, watermelon, and other cucurbit crops. Window-panning is caused when the beetle eats the lower surface and inside of the leaf, leaving the upper surface intact but causing it to turn brown. These insects transmit the pathogen that causes bacterial wilt of cucumber and muskmelon. Infected plants may wilt and die in midseason. Infected plants should be destroyed to reduce the spread of the disease.
The larvae of both cucumber beetle species feed on the roots of various plants but do not cause serious damage.
Life Cycle of the Cucumber Beetle
Adult cucumber beetles overwinter in protected areas and become active and move to newly emerging seedlings or transplants of cucumbers, squash, melons, and pumpkins in spring from mid-April to early June.
Overwintered adults feed for a few weeks, and females lay eggs in the soil around the bases of cucurbit plants. The eggs hatch and larvae feed on the roots for a few weeks before pupating in the soil.
- In southern Illinois, a second generation of striped cucumber beetles develops each season; only one generation occurs farther north.
- In much of Illinois, only one generation of spotted cucumber beetles develops each season, and cold winters in the north may greatly reduce survival.
Management of the Cucumber Beetle
In home gardens, controlling cucumber beetles is often necessary to prevent transmission of bacterial wilt and early death of cucumbers and muskmelons.
- Infestations greater than 1 beetle per plant are often enough to transmit bacterial wilt to a large portion of plants in a garden, so control efforts should strive to keep populations low if disease prevention is the goal.
- Using floating row covers to exclude beetles from plants can provide protection until plants begin to bloom. At this time, row covers must be removed to allow bees to pollinate the flowers.
- Protecting the cucumbers and muskmelons in their early growth stages delays disease transmission and may allow at least a few weeks of harvest even if beetles reach the plants and transmit the pathogen later.
Insecticides can be used to manage beetles.
- Apply as soon as beetles appear in the spring.
- When plants begin to bloom apply insecticides late in the day to avoid spraying pollinators.
- Make sure to read and follow all label directions.
Zucchini and Blue Hubbard squash are especially attractive to cucumber beetles and may offer some value as trap crops.
Contact your county Extension office for current pesticide controls.