Stalk Borer

Every now and then (actually more frequently than I want to admit) I am totally stumped by a question. For example this morning I got a call from a gardener with a new garden spot (this was an important clue) whose tomatoes were dying one by one. She had done some good investigative work on her own and found a small larvae in the stem near the base of the plant. I asked Jim Jacobi, from our plant diagnostic lab and he was briefly stumped but came up with a possibility.

(PICTURE AT RIGHT FROM NCSU - IPM LINK BELOW)

After further investigation I agree with him that the likely culprit is the "Stalk Borer" (Papaipema nebris). As mentioned, the "new garden" comment was an important clue. Apparently this insect is mainly a pest in either "no-till" or recently tilled areas (previously in weeds or grass). According to the information linked above stalk borers tunnel in almost any large stemmed plant. Their host range encompasses at least 44 families and 176 species of plants. Some cultivated crops subject to infestation include corn, cotton, potato, tomato, alfalfa, rye, barley, pepper, spinach, beet, and sugarbeet. Although many weedy plants are infested, giant ragweed is preferred.

On the plus side this is not a serious pest on most garden sites. Tomatoes are not a favorite food source but happen to be the only thing nearby where they overwintered. Pesticides that could be used for control would be those that kill other larval species (check here for products) but I doubt this would be a serious recurring pest.