But more options, in different chemical classes, are now available, says Ed Grafius, professor emeritus and Szendrei’s predecessor at Michigan State University. The downside is that they typically cost more and aren’t as easy to use.
Growers don’t have the luxury of complacency, however.
“You’re not supposed to practice resistance management once it’s biting at your heels,” Groves says.
Newer foliar sprays, including spinosads, insect growth regulators such as novaluron, and abamectin and other mectins are effective options against the first beetle generation, he says. That frees up neonicotinoids for a foliar application against the second generation.
Rotating chemistry classes through the season is vital. If you apply a neonicotinoid at planting, use anything but a foliar neonicotinoid later, says Andrei Alyokhin, associate professor of applied entomology at the University of Maine in Orono.
Abandon the idea of killing every beetle in your fields, Alyokhin says. That only increases the survival chances of resistant genes.
Instead, aim for manageable population levels that minimize economic losses.
Potato plants can tolerate considerable defoliation by the beetle—as much as 30 percent, depending on variety and environmental conditions—without a drop in yields, he says.
Watch your fields closely. The earlier you spot problem numbers, the easier the solution will be, Alyokhin says.
“The biggest concern isn’t what the beetle is doing today,” but the threat from subsequent generations, Grafius says.
Timing is critical. “You make far fewer mistakes when you [apply imidacloprid or thiamethoxam] at planting and it works,” Otto says.Make a mistake—as happened in a couple of his fields last year—and in as little as a week the larvae may be burrowing into the ground to pupate. “Then you fight problems the rest of the season,” he says.
Summer generations fly more as adults than overwintering adults, he says.
That could take them into new fields, undermining a trait growers have relied on to slow the beetles’ spread: They don’t fly far, preferring the ground.
Location, location, location
Wherever possible, planting at least a quarter-mile from other potato fields and maintaining strong crop rotations can limit new infestations, researchers say.
Achieving adequate field separation can be a tricky exercise in choreography with neighboring farms, Groves says. But “it can go a tremendous way to minimizing” problems with Colorado potato beetle.