(Cerotoma trifurcata)
This widely distributed insect attacks all beans, as well as peas. Adult beetles feed on the undersides of leaves, blossoms, and pods throughout the growing season. Grubs feed on the roots and stems below the soil line. Females lay clusters of orange eggs on the soil at the base of plants. The grubs that hatch from these eggs attack the plant below the soil, feeding on the roots and sometimes girdling the stem at the soil level. This feeding can kill the plant. Both adults and grubs cause serious damage to young plants. There are 1 to 3 generations per year.
Apply an insecticide containing carbaryl or diazinon at the first sign of damage. Be sure to spray the undersides of the leaves where the beetles feed. Repeat at intervals of 7 to 10 days whenever damage occurs. Clean all debris from the garden at the end of the season to eliminate overwintering spots for adults.
Plant Care for Beans