Get weed control rightGet weed control right

Many farm fields across the Dakotas are home to soybeans, and there are some big updates for weed control for the 2023 growing season.

“Zero seed production is our goal at the end of the year,” said Joe Ikely, weed specialist with North Dakota State University, during a recent NDSU Extension webinar.

Ideal pigweed control starts before the seed hits the soil. “Getting it right for soybean weed control does start with the foundational preemergence program,” he said.

NDSU research findings showing resistance in pigweed and kochia may have farmers adjusting their herbicide programs to properly control populations in soybean fields.

New herbicide research

A recent multi-state trial studied pigweed control with a pre-application of Metribuzin.

“The concept here is taking another look at Metribuzin for residual weed control,” Ikely said. “If we look at some of our premixes on the market that have Metribuzin, it’s usually a full rate of a Group 14 or 15 herbicide, and then a lower rate of Metribuzin to supplement that herbicide.”

This study flipped that concept on its head, using Metribuzin as the main product for pre-application.

“The results got pretty consistent with the weed control when we got up to 12 to 16 ounces of Metribuzin,” Ikely said.

Results from the study, conducted in Fargo in 2021 and 2022, show Metribuzin gives control over pigweed species in a pre-emergence application. It was also conducted with a Metribuzin-resistant soybean variety, which will be repeated this year as well.

When it comes to weeds in the pigweed family such as waterhemp, the study found control was up to 98% effective four weeks after planting with this Metribuzin mix.

“We saw a definite drop off of residual weed control in waterhemp when we dropped the Metribuzin rate down to half a pound or less,” he said.

Keeping kochia controlled

A recent press release distributed by NDSU detailed how two popular herbicides used in no-till fields no longer control kochia in some regions. In a greenhouse study, Aim and Sharpen were found not to control some populations of kochia in the Minot, Berthold, Mandan and Mott areas.

“We know we have several populations basically in the central and western part of the state, and Saskatchewan,” Ikely said.

NDSU will be conducting extensive greenhouse research on other Group 14 herbicides, such as Sulfentrazone or Flumioxazin to determine their control.

Ikely said they know the resistance to Aim, Sharpen and glyphosate found in North Dakota and Canada is widespread, but more research will be done to determine how widespread resistant populations may be.

“Remaining burndown options on these populations — if we assume Aim and Sharpen won’t work, and we can’t rely on glyphosate due to resistance — leaves a lot of reliance potentially on Gramoxone or Paraquat,” he said. “We can tankmix that with Metribuzin, and that is probably going to be one of the better programs we can use for burndown.”

For more information on weed research from NDSU, visit ag.ndsu.edu/weeds.