Cucumber beetles attack cucurbit crops, like cucumbers (Cucumis sativa), melons (Cucumis melo), summer squashes (Cucurbita pepo) and winter squashes (Cucurbita moscasta, Cucurbita maxima, Cucurbita pepo and Cucurbita argyrosperma). They also frequently carry the plant diseases bacterial wilt and squash mosaic virus. Sometimes you may need to use an insecticide to protect your crop. Organic and inorganic chemicals, and one biological insecticide, can help control cucumber beetles.
Synthetic insecticides vary in their toxicity to the environment. Some are more toxic than others to honeybees. Follow application instructions carefully for each pesticide to avoid killing bees and contaminating runoff water. Some insecticides are no longer available because of their environmental toxicity.
Transplant and Planting Insecticide
When you transplant, the systemic insecticide chloronicotinyl -- 0.235 percent imidacloprid -- will help prevent early damage of young plants. Mix 1/2 ounce in 1 quart of water and apply it as a soil drench or a side dress to 10 square feet of row after planting. There is little to no risk to honeybees because of application timing and little of the insecticide is transported to the flowers from the root system.
Three dust formulations can be used for cucumber beetles: carbaryl, 5 percent; pyrethrin, 1 percent; and rotenone, 1 percent. All of these are toxic to bees, so apply in the evening or early in the morning, when the flowers are closed. Cover all plant surfaces with the dust. Only apply this when you've seen cucumber beetles.
Foliar Liquid Sprays
Liquid insecticides include carbaryl, malathion and a formulation consisting of rotenone and pyrethrin. Malathion has been reported as marginally effective. Malathion in a 50 percent emulsion is added at 1/2 to 1 1/4 fluid ounces per 1 gallon of water to cover 1,000 to 3,500 square feet of garden area. Apply the spray after you've seen cucumber beetles and cover all shoots and leaves on the plants. Repeat if you see beetles a few days later. Malathion cannot be used with carbaryl dusts or liquid sprays because the combination is toxic to the plant. Liquid carbaryl, 23.7 percent, is an alternative to the powdered formula. Add 4 teaspoons of the product per 1 gallon of water to make up the spray solution. Spray to wet all surfaces of the plant thoroughly, and spray in the early morning or late evening when the flowers are closed to prevent toxicity to bees. An organic insecticide, a liquid mixture of rotenone, 1.1 percent, and pyrethrin, 0.8 percent can be used at a rate of 1 teaspoon per 1 gallon of spray mix. Apply as you would apply liquid carbaryl and other liquid insecticides.
Reducing Insecticide Use
Only use insecticides if you see cucumber beeltes. Utah State University Extension Service recommends spraying if you see an average of one beetle per plant when the plants are 4 inches tall. Trap crops of susceptible varieties of cucurbits attract the cucumber beetle early in the season. These specific varieties emit more of the chemicals that attract the beetles, and include "Senator" zucchini. Apply insecticides to the trap crops before the adult beetles lay eggs. You can also minimize insecticide use by planting resistant varieties.
Carefully read the label instructions of all pesticides. Use the proper measuring equipment to ensure the dilution rates are accurate. Don't apply insecticides on windy days and use protective clothing to prevent accidental contact with the insecticides.
- National Sustainable Agricultural Information Service: Cucumber Beetles: Organic and Biorational Integrated Pest Management
- University of California Statewide Integrated Pest Management Program: How to Manage Pests - Cucumber Beetle
- Penn State University: Kaolin Clay (Surround)
- Purdue University: Monitoring and Decision Making for Cucumber Beetles on Muskmelon
- Utah State University: Western Striped Cucumber Beetle, Western Spotted Cucumber Beetle
- Ohio State University: Striped Cumber Beetle
- Oregon State University: Least Toxic and Organic Pesticides for Gardeners
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