Unspoken Truth About Pests: Weather's Influential Role in Pest Pressure This Year

As drought continues to plague farmers in the Northern Plains and Northwest, more record-setting heat is also forecast for next week.

“We have several fields here that are in tough shape,” says Terry Angvick, a farmer in Sheridan County, Mont. “The average spring wheat or durum crop in this year is 35 bushels per acre. I’m projecting half of normal.”

The dry weather and relentless heat weren’t the only factor eating into yields. Grasshoppers infested drought-stricken fields, an issue Angvick hasn’t seen since the 1980s.

“They will reduce yields significantly, to the point where in some fields there will be no harvest,” he says.

The radar is lighting up! But it's not rain, unfortunately. Just countless grasshoppers flying as high as 10,000 feet above the ground! Thunderstorm chances will increase Sunday evening into early next week, but then it looks to dry out and heat up once again. #mtwx pic.twitter.com/dgTCYgM0Vh — NWS Glasgow (@NWSGlasgow) July 2, 2021

As the grasshoppers grow and become mobile, the pests fly across fields and become more of an issue to control. The problem is so bad this year, the National Weather Service’s radar picked up the swarm.

“Weather is always very influential on pest pressure, a lot of pests' (emergence) time is heat unit based,” says Missy Bauer of B&M Crop Consulting. 

Farm Journal Field Agronomists Ken Ferrie and Missy Bauer say it’s the lack of rains early that start showing up as an issue in the summer months. 

“For us locally [in Heyworth, Ill.], we did not get heavy rains during the rootworm hatch,” says Ferrie, owner of Crop-Tech Consulting. “So, there is a window of opportunity to drown rootworm when the soil is saturated right there at the hatch. We did not get that. So, we're seeing a little bit more rootworm pressure from that situation there.”

Weather's Quick-Switch

In Michigan, not only did farmers not see rains early, but Mother Nature made a quick switch this year.

“I would say my biggest concern here is we went from being extremely dry, where we are on the drought monitor and starting to see a lot of crop stress, to then 13 days of pretty much solid rain,” says Bauer. “And they were big rains, anywhere from 6" to 12".”

She says that sudden change in weather compounds crop stress.

“Now we went from being too dry to saturated soils and really losing a lot of nitrogen,” explains Bauer. “I think it's the added stress that's probably going to be our bigger factor. So, let's say now we do end up with some sort of insect pressure, but we've already had all these compounding stresses on top of it, I’m more concerned about just the added stress from it.”

Ferrie says more so than the issue of too dry or too wet, it’s the heat – and lack of heat – that can be often be a problem when it comes to pests. (Read more about the "Unspoken Truth About Pests" here.)

“For insects, it's not always the dry or wet situation, we track insects by insect GDU,” he says. “That becomes part of their development, so we know when the actual infestation is going to take place.”

Wind Direction/Speed

The other major factor: winds.

“Other things that in the weather that affect insects is those that blow up from the South,” adds Ferrie. “Your southerly winds, for instance, bring in our cutworm populations and maybe our southwestern corn borer, stuff like that.”

From wind direction, including velocity of the gusts, it comes with increased pest pressure risks.

“Things like armyworm, black cutworm, moths, those are all things that really blow up from the southern areas into our area,” adds Bauer. “And then once they get here, then we again go back to heat unit based on when things actually hatch after the eggs are laid from the moths.”

For 2021, University of Illinois Extension entomologist Nick Seiter says weather hasn’t played a major role in the eastern Corn Belt.

“We haven't seen dramatic impacts of the weather on pest populations this year,” he says. “Spider mites are a great example of a pest that weather leads to when you have very wet weather, particularly when you have that at the wrong time, or the right time, I guess, if you're trying to get rid of corn rootworm.”

From very wet conditions, to even the extremes of flooding, the amount of moisture can drown out issues in a given year.

“If you have flooding conditions when those eggs are hatching, you can have pretty dramatic negative impact on that population and reduce corn rootworm pressure,” says Seiter. “We haven't had either of those situations this year, but those are prime examples.”

Major Misconceptions

As farmers and agronomists hit the fields to scout, agronomists and entomologists say there’s one major misconception when it comes to weather’s impact on insect populations that year.

“I think probably one of the big misconceptions is the winter,” says Bauer. “People always say, ‘Oh, it was this type of winter or that type of winter, and that's going to influence my pest pressure.’” There might be a little bit of truth to some of that. But remember, so many of these pests do overwinter in other places and get blown in with the moths and the wind currents.”

It's a misconception voiced from Michigan to Ohio.

“The thing that I get asked every time we have a cold winter is will the cold winter affect the insect populations, will there be fewer insects, and I’m always very sad to tell people, ‘No, not really,’” says Kelly Tilmon, field crop entomologist with Ohio State University. “I do get this question a lot, but the fact is that insects are very well adapted to live in the climates where they occur, even the extremes of those climates.”

“When we have a hard winter, some farmers think that's really going to come through and take out a lot of our pest population,” adds Seiter. “That happens to some extent, but most of the insects that we deal with regularly in Illinois, particularly things like corn rootworm, Japanese beetle and bean leaf beetle, they're pretty well adapted to an Illinois winter.”

Ferrie says farmers also think an abrupt change in weather can cause new pest problems to pop up.

“Two dry days don't create a spider mite issue, and two wet days don't create a disease issue in the corn,” says Ferrie.

Instead, Ferrie points out by the time farmers notice heavy infestation issues, it’s probably been a problem for weeks. 

“Most of the time we're looking at two- to three-week weather patterns that set us up. It's not as quick as some people want to believe,” he says.

The Farm Journal team is digging into details of pest pressures in an ongoing series called "Unspoken Truth About Pests." Read more about battling pest pressures, including five ways to be a better scout, here. 

Join Ken Ferrie and team for the 2021 Farm Journal Corn and Soybean College in Heyworth, Ill. The two-day event starts Tuesday, August 3 at 8 a.m. From nature and climate, to the implication of soil types, the team at Crop-Tech Consulting will help farmers create a successful plan that can adjust as the environments change.