Research Highlights

Outsmarting Weeds in Western Kansas Soybeans

Soybean acres have been expanding in western Kansas over the last decade due to improved genetics and increased grower interest to introduce a legume into their crop rotations. But the age-old problem of weed control is an issue here just like everywhere else.

“Regardless of the crop — whether it’s corn, grain, sorghum or soybeans — there are two main species of weeds problematic in western Kansas: kochia and Palmer amaranth,” said Andrew Tucker, assistant agronomy professor at Fort Hays State University. “Kochia is an early problem and Palmer amaranth becomes an issue later in the growing season.”

Tucker is exploring additional ways to control these two weeds through cultural methods that support herbicide regimens on dryland soybean fields. Changing row spacing and planting dates could make a difference in weed suppression. He and Vipan Kumar, a weed science assistant professor at Kansas State University, are conducting research that explores these methods through a project supported by the Kansas Soybean Commission.

“Residual and burndown herbicides focus on the kochia because that’s the first problem we see in the spring,” Tucker said. “Oftentimes the herbicide doesn’t have long-enough residual to take care of the Palmer amaranth. If row spacing were narrowed or seeding dates changed that are appropriate for western Kansas, we could re-write some of the best management practices.”

Tucker tells his weed science students that the best herbicide in the world is darkness. Plants, including weeds, need sunlight to grow. He believes that narrow rows will definitely have an impact on weed suppression.  And delaying soybean planting until a little past traditional seeding dates could also have benefits.

“If we can get that first flush of Palmer amaranth burned down early in the growing season and also delay planting — that could be another strategy,” he said. “Later canopied soybeans could reduce Palmer amaranth growth in the late summer and early fall and save farmers an additional herbicide pass,” Tucker said.

It’s difficult to arrive at conclusions with only one season’s worth of data, but they did notice a few promising results. Tucker found the soybeans planted in narrow, 15-inch rows reached canopy about four weeks ahead of those in 30-inch rows. Nor did they see a yield penalty in the 15-inch rows, which is what is been historically in drier areas like western Kansas, as the narrowly planted soybeans drive water usage.

“This could be a game-changer if the results are replicated this year. We will know more after harvest,” Tucker said. “The quicker we can get the canopy to develop and close, then we give our crop a competitive advantage over weeds. Using these cultural control practices could go a long way to help reduce weed pressure, but we may have to change our line of thinking.”

Published: Oct 12, 2020