Wheat farmers now contending with weeds left after harvest
K-State’s Peterson outlines new control options
July 18, 2019
MANHATTAN, Kan. — As the Kansas wheat harvest winds down, farmers likely are turning their attention to another bit of business in those same fields.
“With all the moisture we’ve gotten in the state this spring and summer, the weeds have come on,” said Dallas Peterson, a weed management specialist with K-State Research and Extension.
Previously-flooded areas and other bare spots are prime locations for weeds, Peterson said. Plus, harvesting wheat means there are now more open areas for weeds to grow.
“We need to get on these (weeds) as soon as possible, especially in those areas where weeds were present when we were harvesting wheat,” he said. “They’re going to be tough to control.
“One thing we do have going for us is we are not limited on moisture; weeds are always more susceptible when they’re actively growing and not stressed, so that’s a good thing. But they are at an advanced stage of growth, and that does make them difficult to control.”
In past years, glyphosate has been the go-to herbicide to control most weeds, but Peterson notes that many species – including marestail, kochia and Palmer amaranth -- have become resistant to glyphosate.
And, he adds, “in many cases the 2,4-D and the dicamba are not doing the job either, partly because in many cases we let the weeds get too big for them to control.”
Peterson said that farmers may need to consider alternative products, such as paraquat or flumioxazin, as effective weed management options.
Paraquat works well to control emerged pigweed and kochia. It can be used in tank mixes with atrazine, metribuzin, dicamba, 2,4-D and others. “We tend to get better long-term control with those tank mixes than when we use straight paraquat,” Peterson said.
“Wharpen is another herbicide that can be used as an alternative or tank-mix partner with other herbicides for burn-down of exiting weeds, as well as some residual control,” he said.
Flumioxazin is an herbicide used primarily in soybeans in the past, but Peterson said it may be beneficial as a tank mix partner for extended residual control of weeds in wheat stubble. “This is especially true in wetter summers,” he said, “which result in multiple flushes of pigweed and kochia.”
“The advantage to using the flumioxazin is the residual control, especially pigweed control,” Peterson said. “There’s a range of rates we can use, but probably 2-3 ounces per acre is the best. The main difference you’re going to see is the amount of residual control it provides.”
Farmers are encouraged to visit with their local extension agent for specific advice in their fields. They can also get updated recommendations from K-State in the annual publication, Chemical Weed Control for Field Crops, available online.
“We got spoiled when glyphosate was still working,” Peterson said. “It would control big weeds. Most other herbicides are not going to control the large weeds nearly as well. Even though some of these do have some residual, there are limits to that too; it’s not going to last forever.”
Ongoing updates from K-State’s Department of Agronomy are available each Friday in the weekly e-Update.