Colorado potato beetles are a challenge to control. Sometimes control efforts fail because the insects tolerate the insecticide that is used against them. It takes some trial and error to find the best choice for your garden. What works well in one part of the region may be ineffective in another.
Several factors can contribute to Colorado potato beetle control failures. Timing of sprays is critical. Spraying too early and only once may only control a portion of the beetles. Follow-up sprays may be needed to keep beetle numbers down. Unfortunately, waiting until larvae are large (nearly full grown) also increases the chances of control failure. Small larvae are much easier to control with an insecticide than large ones.
Insecticides should only be used when needed. Potato plants can withstand considerable defoliation (up to 30%) without yield loss. Additionally, some beneficial insects such as birds, predatory stink bugs, and parasitic flies will help to reduce Colorado potato beetle numbers. Other non-chemical control measures such as hand picking of adult beetles and immature stages is encouraged, as this will help delay the development of resistance.
Contact your local Extension office for insecticide recommendations. It is important to select from different groups of insecticides if you are not satisfied with your results.
You may want to read the following extension publication from the University of Kentucky: COLORADO POTATO BEETLE MANAGEMENT.
