The first generation adults of the Colorado potato beetle (CPB) have emerged and are active on potato, eggplant, and, to a lesser extent, tomatoes. CPB can surprise growers (particularly backyard growers that don’t regularly scout for insect pests) because larvae grow quickly and ravage plants seemingly overnight. Among our insect pests, CPB is notorious for its ability to develop resistance to commonly used insecticides. In fact, it has been shown to develop resistance to most classes of insecticides in a matter of just a few years.
CPB lays its yellowish-orange eggs in clusters of 15 to 25 on the undersides of leaves. Initially the reddish brown larvae feed in small clusters (Figure 1), but after molting they begin to disperse on plants.
Larvae pupate in the soil and later emerge as adults (Figure 2).
Nine different classes of insecticides are listed in UK’s Vegetable Production Guide for Commercial Growers (ID-36) to control CPB on potatoes. In some areas of the state, some of these IRAC classes are not effective because CPB have developed resistance. CPB may develop resistance to remaining classes if these insecticides are overused.
Here are some guidelines to avoid or at least delay the development of resistance by CPB.
1.) Only use an insecticide against CPB when needed. Potato plants can tolerate up to 30% defoliation without yield loss. In small plots or backyard gardens, hand picking may be a control tactic when the numbers of CPB are small.
2.) If insecticides are used, rotate insecticides with different modes of action with each new generation of CPB. IRAC group numbers on insecticide labels can be used to select materials with different modes of action. It takes about one month for CPB to complete a generation and there are two generations per year in Kentucky.
3.) Be sure to use the insecticides at the labeled rates. Producers should understand how to translate the labeled rate to the amount needed for their field or garden.
By Ric Bessin, Extension Entomologist