K-State Field Crop Entomologist Recommends Waiting To Treat Wheat For Insect Pests

By Maddy Rohr

A wave of warm weather in the middle of February may draw the attention to winter grain mites – a concern to many farmers – but Kansas State University field crop entomologist Jeff Whitworth said they aren’t doing any damage right now.

“Most winter grain mites are in the egg stage right now. There are a few active nymphs and adults, but most are in the egg stage,” Whitworth said. “If you go out on a warmer night with a flashlight you can see some feeding on the leaves, but if it is colder, they will be down in the soil not really doing any damage.”

According to Whitworth, three pests may cause concern early in the season: winter grain mites, army cutworms and Hessian flies. Whitworth said all three are most active in late fall to early winter.

“Once temperatures drop, winter grain mites die off and just their eggs are left during winter, but army cutworms will be feeding anytime the temperatures are over 45-50 degrees Fahrenheit,” Whitworth said.

“The hessian fly is dormant right now, but if you have places in your wheat field last fall that looked like they’re going backwards or dying with dark blue-gray colored leaves, pull those up and you’ll see little mahogany colored, cigar-shaped flaxseed. That's the resting stage of the hessian fly.”

When the weather consistently becomes warmer, these three pests mature and may cause damage.

“If the crops are still dormant, pests won’t feed on them very much. Even if they do, it's not going to cause any problems. It's once these crops -- mainly wheat -- come out of dormancy and start growing that we start having a problem,” Whitworth said.

Lack of soil moisture will add to pest-caused damage once crops break dormancy.

“That damage is going to show even more because those plants are also struggling for moisture,” Whitworth said. “It is a good idea to go out and try and figure out where those populations are, but you don't need to do anything about them right now.”

Whitworth recommends sampling or monitoring the weak or thin areas to determine if the cause is pest-related and plan your action based upon pest identification. It is best to wait until plants have broken dormancy because pesticides do not work as well below 50 degrees F.

“So even if pests do feed on plants, it's not going to impact the spring growth or the yield because the roots are already set. Don't worry about trying to find a solution until everything breaks dormancy,” he said.