Armyworm

A yellow-striped armyworm found in an Iowa field by researchers.

After an eventful planting season, farmers have finally had time to settle into their normal routines. That means dealing with the next set of challenges: pests and diseases.

Matt Blasberg, the location manager for Farmers Win Co-op in Bremer County, Iowa, said waterhemp has been an issue for some varieties of soybeans in his northeast Iowa location, but corn hasn’t had any major issues so far.

That could change with a chance for disease and mold moving into the area.

“So far everything looks OK, but with the hot and humid weather coming in and a storm down in the Gulf (of Mexico), it could push stuff up from the south at us,” Blasberg said. “I expect the fungicide season to be big in this area.”

In other parts of Iowa, the message is similar. Things are relatively quiet now, but crop challenges could ramp up any minute.

Farmers in the Afton, Iowa, area have been dealing with the usual weeds such as waterhemp and marestail, according to Willie Smith, a United Farmers’ Cooperative location manager.

With the challenges of the spring causing planting delays, Smith said diseases are also behind.

“Between fighting the rains and late going, we are still going,” Smith said. “It’s been quite a different year here. We aren’t far enough into the stages to know yet. We haven’t had to deal with (any of the pests) yet, so we’ve been pretty lucky.”

Blasberg said the only insect pressure his area has seen is from Japanese beetles.

One pest grabbing headlines recently is thistle caterpillar, which can be a soybean threat. It was found in certain parts of Iowa, including at some Iowa State Extension research farms, according to a July 12 blog post by Extension entomology specialist Erin Hodgson.

In the post, she said she has also seen green cloverworm, soybean looper, alfalfa caterpillar, yellow-striped armyworm, true armyworm and black cutworm.

Similar observations have been made in Nebraska and South Dakota.

Robert Wright, an Extension entomologist with the University of Nebraska, said in post on the university’s Crop Watch website that the best way to assess damage from thistle caterpillar is to determine defoliation over an entire soybean canopy and “consider treatment if insects are present and defoliation will exceed 30%.”

Some insecticides work against the caterpillars, he noted.

Another pest to keep an eye on is corn rootworm, said Jeremiah Mullock, BASF insecticide and nematicide lead. The eggs from last summer may have begun hatching, and if not treated during the pre-planting stage could cause major yield loss.

He said crop rotation is effective to stop corn rootworm from being too troublesome, but farmers opting to go corn on corn add to the risk.

“If you can control those larvae, you’ll have fewer adults come up,” Mullock said. “Crop rotation is a good strategy because you can cut down on overall egg lay. (Not having crop rotation) makes it very difficult because you are taking a key pillar out of a strategy. Then you have to focus on controlling the adult population and doing the best you can in-season.”

He said the best indicator for rootworm issues is to look at last year’s population. If there were numerous adults, chances are good there will be numerous eggs hatching the next season.

Sign up for our weekly CropWatch newsletter

* I understand and agree that registration on or use of this site constitutes agreement to its user agreement and privacy policy.