What Insect Spray Do I Use for Broccoli?

Without protection from common insect pests, broccoli plants might wither and die or produce flower heads infested with cabbage worms. Safe and effective sprays eliminate two of the most common broccoli pests without resorting to chemical insecticides. A third problem needs a stronger solution and requires chemical treatment of soil at planting time.

The insects that cause the most serious problems for a broccoli crop include the cabbage root maggot, the common aphid, and three varieties of caterpillars. A small white moth called the European cabbage moth visits the plants during the day and lays the eggs, which hatch into cabbage worms. A brown-and-gray nocturnal moth deposits eggs that become cabbage loopers; a gray moth with diamond-shaped wing patterns infests the plants with diamondback larvae.

A small fly deposits eggs in soil cracks near young broccoli plants, and the maggots hatch below ground, out of reach of chemical sprays. An infested plant yellows and dies after a few weeks as the maggots destroy its root system. Insecticide granules scattered in the planting furrow offer protection. Add carbaryl or permethrin at planting time to prevent cabbage root maggot problems, notes the Virginia Cooperative Extension.

Aphids cluster on the underside of leaves and along tender stems, feeding on the broccoli plant's sap and stunting growth. Predator insects including lacewings and ladybugs offer some natural control, but insecticidal soap gives faster results. Spraying thoroughly with an insecticidal soap solution on a warm morning coats the aphids, and 30 minutes of drying time kills the bugs, says entomologist Jack DeAngelis. Rinse off the soap with clean water to prevent damage to plant leaves.

A spray containing bacillus thuringiensis coats the broccoli plant with disease spores that are deadly to caterpillars but harmless to humans. As the caterpillar feeds, the worm ingests the bacteria and quickly becomes infected. Infected worms stop feeding and soon die. Apply the spray every four days for continued protection, recommends entomologist Eric R. Day of Virginia Tech. Cabbage moths lay eggs on cole crops throughout the growing season. For a fast-acting alternative consider permethrin, a contact poison. Permethrin offers immediate control of both aphids and caterpillars.