Question: I have had problems with striped yellow and black beetles eating my tomatoes and eggplant since mid-summer. I have pulled out the infested plants, but noticed they are in the soil. Is there anything I can do to treat the soil so that I do not start with the same problem next spring?
Answer: Colorado potato beetles are significant pests for potato, tomato, eggplant, pepper and various weeds including ground-cherry, jimsonweed, horse nettle, petunia, henbane, thorn apple, thistle and mullein.
The adult beetle is hard shelled and about ⅜-inch long and ¼-inch wide. It is bright yellow with 10 longitudinal black lines on its wing covers and black spots on the thorax. The larva, or “slug,” is a soft-skinned, humpbacked, very fat and brick-red in color with two rows of black dots on each side of the body. If left unchecked, these beetles will defoliate plants and burrow into fruit, reducing yields and ultimately killing most of the plants.
These beetles first emerge in spring, just about the same time as new potato vegetation. Females lay their bright yellow-orange eggs in clusters on the undersides of leaves of host plants. The eggs hatch into larvae which feed for about 3 weeks, passing through four larval stages, the last of which enters the soil to pupate. Adult beetles emerge from the soil in about 1 to 2 weeks to lay eggs for a second generation. This second generation is seen in late summer and occasionally, under the right conditions, will create a small third generation in fall before burrowing into the soil to overwinter as adults. Overwintering adults will burrow 4 to nearly 12 inches into the soil, often choosing protected areas near trees or in grassy edges surrounding gardens or fields.
Control in the home garden can be very difficult, and most of the pesticides available to home gardens are ineffective. It is critical that cultural control be practiced to reduce the number of beetles. Handpick potato beetles, as well as their larvae and eggs, and drop them in a bucket of soapy water to destroy them. Be sure to wash your hands before touching your skin after handling these beetles as they release a chemical that can be irritating to sensitive skin.
When handpicking is not practical, you can spray the potato plants with Bacillus thuringiensis. This naturally occurring soil bacterium paralyzes the gut of potato bugs, slowly starving them. Read package labeling, though, and buy Bt labeled specifically for use on potato bugs, since many products work only on moth larvae.
Tilling the soil in late fall or early spring can kill overwintering potato bugs, reducing their numbers. Be sure to remove all plant debris in the fall to reduce protected spaces for them to overwinter.
Because these bugs can fly long distances to find a host plant, crop rotation is unlikely to be effective in the home garden. When planning your garden for next year, you can reduce your chances of another infestation by choosing early maturing varieties of potatoes and using floating row covers in the spring to protect seedlings.
For more information on Colorado potato beetles and other pests in the garden, you can contact your local extension office. Atlantic County residents can contact the Master Gardener Helpline at 609-625-0056. Cape May County Residents can call 609-465-5115, ext.3607.
Events: Atlantic County Master Gardeners will be available to answer gardening questions and take samples for plant identification or diagnoses throughout the county the fall. You can find us at the Hammonton Green Day Festival, Sept. 21. We will also be available at Atlantic County Library branches throughout the county evenings in the fall. Please check with your local library for a schedule or call the Master Gardener Helpline for dates and times near you.
Interested in our Junior Master Gardener Program? We will have an information session Sept. 16 at 6 p.m. at the Rutgers Cooperative Extension Office in Mays Landing. Call 609-625-0056 and ask for Brittany Rigg or Kendrin Dyitt for more information.
Do you have a gardening related question you would like answered here? Please forward your questions to Belinda Chester, Master Gardener Program Coordinator, Rutgers Cooperative Extension Office, 6260 Old Harding Highway, Mays Landing, NJ 08330. You can also submit questions at Rutgers-atlantic.org/garden or email them to email@example.com; please include “garden question” in the subject line.