There are two types of cucumber beetle that belong to the Diabrotica family. The striped or spotted cucumber beetle varieties are both considered harmful garden pests, and can do extensive damage to not only cucumber plants, but to many other vegetables and ornamental plants. They are yellow-green or orange in color with either black stripes or spots and are quite small — just 1/4 inch (6.4 mm) long. Cucumber beetles harm vegetation in the larvae stage by eating small, tender young plants as they emerge from the soil, and by burrowing into the ground and feeding on the roots. Adults eat the flowers, leaves, and stems of larger plants.
Although cucumbers are their preferred food, there are well over 200 different plants that these pests will eat. Other cucurbits such as squash and melons are especially prone to damage from these beetles and their larvae. Plants that have yellow flowers, including bean and tomato plants, are the most attractive to them. Eggplant, asparagus, cabbage, and peas are frequently visited by these bugs as well.
The striped cucumber beetle often over winters in northern climates and begins attacking plants in early spring when the temperature reaches about 65° Fahrenheit (18° Celsius). The spotted cucumber beetle is found year round in southern areas, but migrates north in early summer to do its damage. In the south, it also appears several weeks after the striped variety. Cucumber beetles often spend winters in corn fields and compost piles, where they can spread the bacterial wilt and mosaic diseases that live through cold winters in their intestines. These diseases then spread to the next season’s crops.
Cucumber beetles can be controlled by growing plants that repel them, including radishes, calendula, marigolds, and catnip. These may help to keep the cucumber beetles from damaging other nearby plants. These beetles also have many natural predators such as nematodes, soldier beetles, and braconid wasps. Ladybugs are also beneficial because they eat the beetle eggs. These insects can purchased and introduced to an area with cucumber beetle infestations.
There are many other ways to discourage cucumber beetles without using harmful chemicals. Some gardeners and farmers spread onions skins or wood ashes on the ground near their plants. A spray containing hot peppers and garlic may also help to deter the beetles. It may be necessary to use chemicals such as rotenone or pyrethrum for severe infestations, although they cannot be used on sensitive cucurbit plants.