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Cucumber Beetles

Garden pest · Acalymma vittatum and Diabrotica undecimpunctata

Description​

Cucumber beetles are small leaf beetles that feed on cucumbers, melons, squash, pumpkins, and other cucurbits. In North American gardens, the two familiar types are the striped cucumber beetle (Acalymma vittatum), which has three dark stripes on yellow wing covers, and the spotted cucumber beetle (Diabrotica undecimpunctata), which has dark spots instead. Adults chew leaves, blossoms, stems, and young fruit. Their larvae live in the soil and feed on roots. Seedlings are especially vulnerable: heavy feeding can kill them before they become established. Even a few beetles can matter because they may spread bacterial wilt, a disease that causes cucumber and melon vines to wilt rapidly. Adults can move into a garden from nearby plants, so damage may appear suddenly. They are often most noticeable when plants are young or flowering.

Symptoms​

  • Holes in leaves
  • Wilting
  • Stunted growth
  • Insects visible on the plant
  • Stems chewed or cut through

How to Identify​

Look for beetles about 6 mm (¼ inch) long, with yellow wing covers marked by three black stripes or dark spots. Adults may gather in blossoms and run or fly away when disturbed. Look for irregular feeding holes in leaves, chewed flowers, or shallow scars on fruit. Larvae are pale, slender, and found in soil near roots. Sudden, persistent wilting in a cucumber or melon vine can indicate beetle-transmitted bacterial wilt, even if feeding damage is slight. Unlike cucumber beetles, squash bugs are broader, flattened insects; flea beetles are much smaller and typically jump when disturbed.

Prevention​

Check young plants frequently, especially leaf undersides and blossoms. Use fine-mesh row covers or insect netting from planting until flowering, securing the edges so beetles cannot enter. Remove covers when flowers need pollination, unless you hand-pollinate. Starting with sturdy transplants can help plants withstand early feeding. Clear away crop debris after harvest and manage nearby cucurbit volunteers. Rotate cucurbits where practical, although flying adults can still find the new planting. A well-maintained mulch may make it harder for adults to reach soil to lay eggs. Keep plants watered and growing steadily, but do not rely on vigor alone to prevent bacterial wilt. Choose bacterial-wilt-resistant varieties when available.

Treatment​

Start by checking plants often and knocking beetles into a container of soapy water; early morning, when they are less active, is a good time. Remove a vine that has bacterial wilt: it will not recover, and removal may reduce further spread. If beetles remain numerous, a kaolin-clay product labeled for edible crops can help deter feeding; follow its label and reapply as directed after rain. Protective netting can still help young, nonflowering plants if beetles are removed before it is secured. As a last resort, use an insecticide specifically labeled for cucumber beetles on the crop you are growing, following all application and harvest-interval directions. Avoid treating open flowers or exposing pollinators to spray or residues. Sprays aimed at adults will not reliably control larvae feeding underground, so continue monitoring for new beetles.

Plants Affected​

Acorn Squash, Butternut Squash, Cucumber, Delicata Squash, Kabocha Squash, Pattypan Squash, Pumpkin, Spaghetti Squash, Watermelon, Zucchini

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