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Control weeds early to protect yield

Soybean Watch: Early weed competition affects growth and yield.

Tom J. Bechman, Midwest Crops Editor

May 31, 2024

3 Min Read
A patch of Canada thistle in a soybean field
TROUBLE BREWING: When weed patches are coming back as vigorously as this Canada thistle patch early in the growing season, soybeans will be at a disadvantage. Photos by Tom J. Bechman

Soybeans are up and you’ve checked the stand. What’s next? If you have pesky weeds or thin stands, it’s likely time to hit the field with a timely herbicide application.

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

Patches of perennial weeds like Canada thistle are particularly troublesome. “Even if you burned them down before planting, they could come back,” Gauck says. “The best option may be burning them back with herbicides.

“If they grow for any length of time, damage will be done, even if you take them out later. Soybeans respond by growing taller, with fewer nodes. The more nodes, the more pods and the higher the yield potential. If plants sacrifice nodes to grow taller competing with weeds, you give up potential podding sites for lower yields.”

Beck’s sponsors Soybean Watch ’24.

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

All weeds hurt

More common weeds like tall waterhemp and foxtail also impact yields if allowed to grow too long before removal with herbicides. In southern Minnesota, Chad Kalaher, a Beck’s field agronomist, says crusting and excess rains thinned stands in some fields.

Related:First look for pests in soybeans

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

Gauck agrees. “When I assess stands, if someone is worried about if 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 acre,” he says.

“However, you need two things to make that work,” he explains. “First, plants should be evenly distributed without big gaps. Second, but just as important, you need good weed control. If stands are thin with weeds, then it’s a different battle to maintain yield potential the rest of the season.”

From the field

Issues crop up as the season gets underway across the Midwest. Some are minor now but could become a bigger deal later.

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

In southern Minnesota. Early fields are at V2, and many fields are just emerging. Planting is finally wrapping up. Look for some replanting and thickening of stands. — Dale Viktora, Beck’s field agronomist, southern Minnesota

In eastern Nebraska. Soybeans are maybe 90% planted, with anywhere from 2 to 9 inches of rain again this week. Early-planted soybeans are V2 to V3. Postemergence herbicide applications should come soon. With moisture and moderate temperatures, foxtail and waterhemp are breaking through control. It’s time to get in front of these weeds. — Trey Stephens, Beck’s field agronomist, eastern Nebraska

About the Author(s)

Tom J. Bechman

Midwest Crops Editor, Farm Progress

Tom J. Bechman became the Midwest Crops editor at Farm Progress in 2024 after serving as editor of Indiana Prairie Farmer for 23 years. He joined Farm Progress in 1981 as a field editor, first writing stories to help farmers adjust to a difficult harvest after a tough weather year. His goal today is the same — writing stories that help farmers adjust to a changing environment in a profitable manner.

Bechman knows about Indiana agriculture because he grew up on a small dairy farm and worked with young farmers as a vocational agriculture teacher and FFA advisor before joining Farm Progress. He works closely with Purdue University specialists, Indiana Farm Bureau and commodity groups to cover cutting-edge issues affecting farmers. He specializes in writing crop stories with a focus on obtaining the highest and most economical yields possible.

Tom and his wife, Carla, have four children: Allison, Ashley, Daniel and Kayla, plus eight grandchildren. They raise produce for the food pantry and house 4-H animals for the grandkids on their small acreage near Franklin, Ind.

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