Pest Control for Squash Beetles

Handpicking and Sanitation

• Handpicking and sanitation can control squash beetles. Put on rubber gloves and look for squash beetles on your plants at midday, recommends Purdue University Department of Entomology. As you find larvae, yellow egg masses and adult squash beetles, mash them with your fingers. Adult squash beetles overwinter in plant debris, so you should remove all weeds and cucurbit plant material after the growing season. You can either compost the plant debris or till it into the soil.

Parasitic Wasps

• Parasitic wasps (Pediobius faveolatus) measure 1/8 inch long and are nonstinging beneficial insects that help control squash beetles. The wasp larvae kill squash beetle larvae and form a brown case as they feed on and live inside the larvae. After two weeks, up to 25 mature wasps emerge from each case or “mummy.” To attract parasitic wasps, provide water and plant herbs and small flowers to provide nectar and pollen. You can purchase mummies in mesh bags and secure a bag to your squash plant. Parasitic wasps die after the first frost, so you will have to buy them every year in cool climates.

Spinosad

• Spinosad is a non-synthetic insecticide produced from fermentation. It affects the nervous system of squash beetles and kills the beetles one to two days after contact or ingestion. To prepare a spray, dilute 1/2 teaspoon of spinosad in 1 gallon of water. As soon as you notice squash beetle larvae, thoroughly wet the plant surface with spinosad. Apply again after five days, up to five times each growing season. Do not harvest vegetables until three days after spraying with spinosad. Check the product label because instructions may vary.

Carbaryl

• The chemical insecticide carbaryl is effective against squash beetles. Dilute 1.5 fluid ounces of carbaryl concentrate in 1 gallon of water and spray it on the entire surface of infested plants. Do not return to treated areas until the carbaryl has dried, and do not harvest cucurbits until three days after applying it. If squash beetles return, you can repeat the application every six days, up to six times a year. Check the manufacturer's instructions, as different brands may have different instructions.

Caution

• Avoid spraying spinosad or carbaryl on windy or rainy days, and wear rubber gloves and long sleeves and long pants when you spray. Keep children and pets out of areas where you've sprayed. The same insecticides that control squash beetles are toxic to honeybees. To protect honeybees and other beneficial insects, spray carbaryl early in the morning or late in the evening, and do not spray carbaryl on blooming plants.