Fourlined plant bug (Poecilocapsus lineatus) is a pest each year on a variety of herbaceous plants. Damage appears as contorted leaves with brown to black spots. Frequently, the spots are numerous enough to coalesce into large areas that may consume half or more of the leaf. Plants that are attacked include mint, chrysanthemum, coreopsis, dahlia, veronica, Artemisia, salvia, astilbe, cranesbill geranium, black-eyed Susan, and penstemon.
Close observation reveals the red nymphs hiding in the leaf axils. At this time, they are about 1/8 inch long but will continue to feed and grow to about 1/4 inch long. They will then molt into the 1/4-inch-long adults that are greenish yellow, with four black stripes running the length of the body. The adults are very active runners and fly readily when disturbed. The adults are obvious on the plants because they do not hide. By the end of June, they will have mated and inserted their eggs into plant stems where they will remain until hatching next spring.
Insecticide sprays are effective against these insects, but good coverage is essential. Avoid spraying when the plants are in flower to avoid killing pollinating insects. Acephate (Orthene), bifenthrin (Talstar), carbaryl (Sevin), and cyfluthrin (Tempo) are effective. Insecticidal soap will also be effective with very good coverage and is probably the only option if the bugs are on mint that is used in food. Because the eggs overwinter in the stems, removing plant debris in early spring should reduce their numbers.