Cucumber Beetle Description:
There are two types of cucumber beetles that may attack your garden. The striped cucumber beetle has a yellow body with three black stripes along its back. The spotted cucumber beetle is yellow, with twelve black spots. Both are the same size, roughly a quarter of an inch long. The larvae are white grubs with a brownish head.
Adult cucumber beetles overwinter, and emerge in spring.
They feed on weeds and other plants until their preferred food source, cucurbits (such as cucumbers, squashes, and melons) are available. Once they locate cucurbits, they will feed on the plants, and the females will lay their eggs in the surrounding soil. The eggs hatch, and the larvae feed on below-ground cucurbit roots and stems until they pupate. Then they emerge as adults, and the cycle starts all over again.
Signs of Cucumber Beetle:
Cucumber beetle damage is fairly easy to spot: damage from feeding on the leaves, scarring on the fruit, and girdled stems from feeding larvae. Most commonly, this damage is found on cucumbers, squashes, melons, and pumpkins, but may also be found on tomatoes and other garden crops if cucurbits are unavailable or there are more beetles than the available cucurbits can support.
Effect on Garden Plants:
Girdled stems, chewed leaves, marks on the fruit. The most damage comes from bacterial wilt.
The bacteria is secreted in the beetle's stomach, and when they munch on the plant, they spread it to the plant. The bacteria spreads to the plants vascular system, and causes the leaves to wilt. If not contained (via pruning off infected stems) the wilt will eventually spread and kill the entire plant.
Also, plants infected with bacterial wilt attract more cucumber beetles, who will eat the infected leaves and continue spreading the bacteria throughout the garden.
Organic Control of Cucumber Beetles:
You can protect young cucurbit seedlings from cucumber beetles by covering them right after planting with floating row covers, individual screens, or cones. It's also a good idea to plant cucurbits later in the season -- those planted early (by your neighbors, perhaps) will attract any beetles in the area, and your plants may be spared. Also, remove and destroy (don't compost) plants infected with bacterial wilt immediately so that they wont' attract more beetles to the area. Adult beetles found on plants can be hand-picked and squished.