Chemical Pesticides in IPM

Chemical pesticides certainly are an important component in controlling insects and disease but should be used when other less toxic and cheaper methods are not practical or they fail. When a pesticide is necessary, start with the least toxic pesticide registered for the pest – try horticultural oils or insecticidal soaps. Always rotate pesticides with different modes of action in order to avoid pest resistance.

Rotate Pesticides with Different Modes of Action (MoA)

What does that mean? Pesticides work in different physiological ways to kill a pest. Biologists have categorized all known active ingredients in pesticides by how or by what mechanism they work within the pest. The IRAC (Insecticide Resistance Action Committee) MoA Classification Version 7.1 is current as of June 2011.  This classification currently lists 28 mechanisms and these are known as the ‘modes of action’.  All of the active ingredients listed for a particular category have the same mode of action.

On this document, you will see, for example, that MoA #4 is nicotine and the neonicotinoids and includes 8 different active ingredients. When insecticides from the same MoA group are used time after time, despite the fact that they may be different products with different active ingredients, a small portion of the pest will survive from a natural resistance to that particular mode of action and produce offspring that will also have the resistance. Their population will explode and the use of the same insecticides will be ineffective. 

The current recommendation is to rotate insecticides between at least 3 different MoAs to deter such resistance in pests. Horticultural oils and insecticidal soaps can be added anywhere in a rotation system as they do not have a particular mode of action and do not lead to resistance.