Question: Something is attacking my tomato plants. It is a fat red insect with some black dots. What is it and how do I get rid of it before it eats all my tomato plants?
Answer: The arrival of the potato beetle is at least two weeks earlier than past years. If you looked around further you would most likely also see some yellow and black stripped visitors. Both of these feeding insects are the Colorado potato beetle. The larvae are usually brick red with a humped back, softer looking body and bigger than the adult form at 1 inch long. The adult is yellow with 10 black stripes on the wing covers and approximately 3/8 inch in length.
Also on the undersides of the leaves you can find the orange-yellow eggs in clusters of 20 or so. Both the adults and the larvae feed on the plant, but the adult damage is less severe most of the time. The adults can damage or sever the stem when plants are very young. Older larvae. or the fourth larval instar, are responsible for as much as 75 percent of feeding damage. Because of the abundance of this pest and the rapid growth rate of the larvae, defoliation of the plants often kills them prematurely. Potato foliage is the favorite food of the Colorado potato beetle, followed by eggplant and tomato. However, peppers, ground cherry, petunias are not safe from their attack.
The adult beetle overwinters in the soil, emerges in early spring and quickly begins to lay its eggs on the underside of the leaves of the host plant. The eggs hatch into larvae, and pass through four larval generations, feeding during a three-week period. The last larval stage returns to the soil to pupate followed by adult beetles emerging in one to two weeks to begin laying eggs for the second generation. A second generation of adults begin appearing in late summer.
Control of the Colorado potato beetle has become more difficult over recent years. Many beetle populations have recently developed a resistance to the pesticides that have been used against them. Because of the large size of the beetles, handpicking provides good control for the home gardener. When found they should be dropped in a container of soapy water or rubbing alcohol. Eggs found on leaves should be crushed.
New research has shown an organic insecticide called Bacillus thuringiensis var. tenebrionis, available as Novodor, is also effective on early stages of the larvae with no harm to beneficial insects. It is best applied when the larvae is less than 1/4 of an inch. Application must be thorough because the beetle must eat the substance for it to work.
Mona Bawgus is a certified master gardener and consumer horticulturist with Rutgers Cooperative Extension of Atlantic County. Write to her c/o Rutgers Cooperative Extension, 6260 Old Harding Highway, Mays Landing, NJ 08330. Email: