Where farmers in northeastern Illinois hadn't been able to get into their fields because of rain, henbit makes a colorful ground cover.

CHAMPAIGN, Ill. — With weather delays, corn and soybean farmers may be tempted to go directly to planting and worry about weeds later. University of Illinois weed scientist Aaron Hager and other experts say: Resist the temptation.

“We’re not at the point to abandon your plans,” Hager said. “Successful weed control is the emphasis.”

It starts with a clean seed bed, which may be achieved by pre-plant tillage, effective burndown herbicides or a combination. With rain delays, those chores have been a challenge.

But “starting clean is an absolute necessity,” said Blake Miller, Syngenta agronomic service representative.

He said starting clean, using pre-emergent products with residuals and the latest soybean technology to fight weeds will all be needed for weed control this year and to fight resistant weeds in the long term.

Spring annuals flourish

Miller started to be concerned even before the last batch of rains.

“It’s pretty weedy out there,” he said.

The time crunch in planting may tempt farmers to abandon one of their applications, said Miller who lives in Vermont, Illinois, in Fulton County. He said farmers in that part of western Illinois got off to a little earlier start planting this year, but additional rain has slowed them down as well. Some of the corn that is up is yellow, he said.

Jason Carr, technology development representative at Bayer Crop Science, said in contrast to the tough spring for crops, some weeds are off to “a pretty good start” already. If control isn’t taken now, “we will be in a bad place.”

Purple-, yellow- and white-tinged fields show that winter annuals including henbit, butterweed and chickweed got a strong hold this spring. They may soon die down but will leave plenty of seeds. That is something to think about this fall, Hager said, with possible tillage for fall treatment.

The abundant winter annuals will definitely fortify the seed bank, Miller said. This spring the soil will also have a mat of chickweed, for example, and it will be harder for the soil to dry out. There will be less seed to soil contact in planting, and the weed remnants will provide competition to corn and soybean seeds, he said.

Summer weeds growing

Likewise, the summer annuals mares-tail and waterhemp are up and growing in many parts of the state. They may be hard to control this year, especially if their resistance profile is not clear, Hager said.

Farmers will be using tillage and applications that include residuals plus post application.

Miller has already seen photos of giant ragweed and waterhemp growing this spring. If the weeds get as tall as 6 to 8 inches, they are very tough to control, he said.

Overlapping chemistry is in the answer in some cases, Carr said.

Carr emphasized the importance of following the recommendations on the herbicides, including paying close attention to the size of weeds. Also, close attention has to be paid to the restrictions on dicamba to make sure the spray stays on target and on site.

Hager said some people have expressed concerns about the cutoff dates for dicamba use with the planting delays.

Revisit plans

Mike Koenigs, market development specialist for Corteva Agriscience, has seen some challenging years for weed control. The challenges this spring are compounded by the wet fall of 2018, when many farmers didn’t get fall tillage or burndown completed. It was too wet to carry out traditional weed control plans at the usual time after harvest.

“It’s the same recipe this spring,” he said.

Most farmers have a strong weed control plan in place which includes consideration of modes of action, Koenigs said. These plans may have been disrupted a bit because of timing, but the general management practices are set for specific farms.

Farmers may be tempted to deconstruct their plans, but that raises concern when thinking about building long-term resistance to some herbicides, Miller said. He hopes farmers will stick with at least two applications of herbicide on waterhemp.

In choosing products this year, farmers will want to look for flexibly. Some products must be applied before emergence, Koenigs said.

He is expecting challenges with weed control especially for soybeans, where there are even fewer options. It’s important to know what weeds are problems in a field and to dial in those burndown recipes, he said. Marestail, for example, gets significantly harder to control if it isn’t tackled early.

Waterhemp and its cousin Palmer amaranth are the high-anxiety weeds in corn this year, Koenigs said, and giant ragweed remains near the top of the list, with morning glory species also being especially problematic in certain areas. The big germination window of many of these weeds adds to the challenge of controlling them.

Koenigs encourages farmers to try to stay the course with their plans, which may require some “beefing up” this year.

“When it does dry up it will be an absolute race,” Koenigs said.

Phyllis Coulter is Northern Illinois field editor, writing for Illinois Farmer Today, Iowa Farmer Today and Missouri Farmer Today.