7/28/2013 6:00:00 AM Cucumber beetles harmful, but not hard to defeat
The striped cucumber beetle
The spotted cucumber beetle
Linda L. Reddick Master Gardener
There are two cucumber beetles - the striped cucumber beetle (Acalymma vittatum) and the spotted cucumber beetle (Diabrotica undecimpunctata).
Both beetles are about a quarter of an inch long and yellow-green in color. The striped cucumber beetle has three black stripes on its back, and the spotted cucumber beetle has twelve black spots on its back.
Both cucumber beetles feed on emerging seedlings. Adult beetles can retard development or even kill young plants. Later, they may amass in large numbers in the flowers of squash or melons and may chew pits in fruit.
Larvae feed on the roots, causing little apparent injury, but may move into the rind of ripening melons fruit on the soil surface. Adult beetles transmit bacteria (Erwinia tracheiphila) that produce bacterial wilt in cucurbits (the squash and melon family) and cucumber mosaic virus. Both diseases can kill pants.
Typically there are two generations per year. Adults overwinter in leaves and debris, emerging as temperatures warm in the spring to feed on several different trees and shrubs.
When squash or cucumber seedlings emerge, they begin chewing on them. Seedling damage occurs at this time, and plants may become infected with the bacteria or virus.
Eggs are laid in the cracks of the soil around the base of the plants. The eggs hatch in about 10 days and begin feeding on the roots and stems of sprouting plants.
The slender white larvae reach half an inch in length, burrow into the soil and feed on the plant roots for about a month. They then pupate in the soil, later emerging as adult beetles and start the cycle all over again.
Getting control may not be as hard as you think. Spade the soil before planting to destroy dormant beetles. Crop rotation is a great way to prevent buildup of pathogens in the soil that are specific to that type of crop. When crops are replanted year after year in the same location, pests, insects and diseases will tend to build up, especially if the same controlling method is used.
Plant the disease-resistant varieties of cucumbers, melons, pumpkins and squash. Cover developing plants with row covers or cheese cloth to protect them from adult egg laying and feeding.
Encourage beneficial insects such as braconid wasps, tachinid flies and soldier beetles, or purchase some beneficial nematodes.
Horticultural oil or insecticidal soap can be used on overcast or cloudy days. It is necessary to spray both the top and bottom sides of the leaves, and most likely repeated application will be required.
For heavy infestations, use an insecticide containing pyrethrin or an insecticide that is labeled for the control of cucumber beetles. Always read and follow the manufacturer's label directions. And keep in mind that insecticides also kill the beneficial insects.