Crop rotations avoid insecticide resistant bugs

A potato beetle researcher recommends farmers alternate crop rotations and insecticides to avoid building up insect populations that are resistant to the chemicals.

University of Maine associate professor of applied entomology Andrei Alyokhin shared his tips during the Washington Oregon Potato Conference in Kennewick, Wash.

Alyokhin advises using crop rotations and alternating different insecticide applications instead of continuous cropping or repeated applications of the same insecticide.

Treating problem areas is better than treating an entire field, Alyokhin said.

The goal should be to have a small enough population of insects that they won’t cause much damage, Alyokhin said.

“The job is not to kill every single insect,” he said.

When two parent insects that are susceptible to an insecticide mate, all progeny are susceptible. When two resistant parents mate, all progeny are resistant, Alyokhin said.

The progeny of a susceptible parent and resistant parent is usually less resistant than the resistant parent but not as susceptible as the susceptible parent.

The likelihood of resistant offspring declines as resistant insects mate with less resistant partners, but some progeny can still be resistant, Alyokhin said.

If there is some kind of reservoir of susceptible insects, then you are in good shape,” Alyokhin said.

Using as little insecticide as possible is important, but Alyokhin emphasized using the full label rate of insecticides when it is needed.

According to Alyokhin’s website, the Insecticide Resistance Action Committee classifies chemicals according to similarities in their chemical structures and how they kill their target pest. Different chemical groups are designated by numbers and subgroups with letters, such as 1A or 1b or 4.

Alyokhin recommends rotating numbers more than letters. If another application is needed, hitting insects with the same chemical eliminates susceptible survivors but increases the chances of one resistant insect mating with another and producing resistant offspring.

Rotation won’t always work, but is the best option, Alyokhin said.

Farmers who suspect they have a problem should contact a university extension specialist or crop consultant, Alyokhin said.

“Try being vigilant, not relying on spraying the same insecticides over and over again and do not cut insecticide rates,” he said.