Control weeds early to protect yields

The soybeans are gone and you have checked the status. What’s next? If you’re dealing with nuisance weeds or thin stems, it’s probably time to hit the field with a timely herbicide application.

“We can’t afford to let weeds grow for very long,” says Steve Gauck, regional agronomy manager at Beck’s, Greensburg, Indiana. “It’s surprising how quickly weeds impact the soybean plants growing around them. If you don’t act quickly, you can expect lower returns.”

Areas with perennial weeds such as Canada thistle are especially difficult. “Even if you burn them off before planting, they can come back,” Gauck says. “The best option may be to burn them back with herbicides.

“If they continue to grow for a while, damage will be done even if you remove them later. Soybeans respond by growing larger, with fewer nodes. The more nodes, the more pods and the higher the yield potential. When plants sacrifice nodes to grow taller and compete with weeds, you give up potential pod locations for lower yields.”

Beck’s sponsors Soybean Watch ’24.

A man standing in a soybean field, holding a soy plant by the roots in each hand

All the weeds hurt

More common weeds, such as tall waterhemp and foxtail, also affect yields if left to grow too long before being removed with herbicides. In southern Minnesota, Chad Kalaher, an agronomist at Beck’s, says some fields are experiencing crusting and excessive rainfall.

Related:First, look for pests in soybeans

“For some of these thinner stands, timely and proactive weed control will be crucial,” he says.

Gauck agrees. “When I’m assessing stands and someone is concerned about whether the field is good enough to leave, I usually recommend keeping it as long as there are 80,000 plants, and sometimes as low as 70,000 plants per hectare,” he says.

“For that to work, however, you need two things,” he explains. “First, the plants should be evenly spaced, without large gaps. Second, but just as important, you need good weed control. If stands are thin with weeds, then maintaining yield potential for the remainder of the season is a different battle.”

Of the field

Problems are emerging as the season gets underway in the Midwest. Some are minor now, but could become a bigger problem later.

In Illinois. Soybean planting progress finally reached 50% to 60% in eastern Illinois by May 20. Due to both early starts and later planting delays, soybeans range from the V3 stage to still in the bag or box. In addition to weeds, agronomists also look for early season diseases such as pythium and phytophthora root, especially in fields with poor drainage. – Chad Kalaher, field agronomist from Beck, eastern Illinois

In southern Minnesota. The first fields are on V2, and many fields are just emerging. Planting is finally completed. Look for replanting and thickening of the stands. – Dale Viktora, field agronomist from Beck, southern Minnesota

In eastern Nebraska. The soybeans are perhaps 90% planted, with somewhere between 2 and 10 inches of rain again this week. Early planted soybeans are V2 to V3. Postemergence herbicide applications should occur soon. With moisture and moderate temperatures, foxtail and waterhemp break through control. It’s time to face these weeds. — Trey Stephens, agronomist from Beck’s, eastern Nebraska

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