Weed resistance was a bigger issue than ever for many soybean producers in 2012 in Iowa and other Midwest states. "I was shocked by the number of weeds and the different species of weeds I saw in grower's soybean fields during the growing season last year, weeds that could not be controlled with glyphosate," says Matt Hubsch, senior agronomist with Legend Seeds.
What was even more concerning to Hubsch was the number of glyphosate resistant weeds which also had multiple resistances to other herbicides in their background.
"A good example of these would be kochia and waterhemp. Both of these weed species are known to have resistance to ALS (acetolactate synthase) or amino acid synthesis inhibitors, which really complicates the issue," he says.
Because corn and soybean growers can no longer control these weeds with multiple chemistries -- such as glyphosate or ALS chemistries -- their options are fairly limited, explains Hubsch.
One option Hubsch suggests growers consider is using a postemergence Protoporphyrinogen oxidase, or PPO, inhibitor herbicide. "A PPO can work post-emergence on these weed species if spraying is done in a timely manner," he says. "These chemistries do not translocate throughout the plant like glyphosate or ALS chemistries, so getting good coverage with the herbicide spraying is crucial."
Preemergence herbicides are key to managing glyphosate-resistant weeds
Treatments with herbicides like Flexstar or Cobra have to be done early, post-emergence, when weeds are small. Since coverage is essential, Hubsch recommends applying heavy amounts of spray volume (using an herbicide mixture in a volume that is between 15 and 20 gallons of water).
"The use of preplant/preemergence herbicides is going to be a primary 'tool' in managing glyphosate resistant or tolerant kochia or waterhemp," Hubsch says.
Products like Authority Assist, Authority MTZ DF, Sonic, Authority First and Valor will be key residual preplant/preemergence herbicides that will help reduce the potential financial losses that may ensue from glyphosate resistant weeds, he adds.
Be proactive, act now before the weed resistance problem gets out of hand
"We have been hearing some real horror stories from the southeastern U.S. soybean- producing states. Stories of farmers losing their farms due to glyphosate resistant weeds such as palmer amaranth or incredible cost accrued from hand-weeding of soybean fields," Hubsch says. "Being proactive with managing weeds that may be confirmed or are showing signs of glyphosate resistance in your fields is critical."
To avoid these issues, Hubsch encourages growers to use preplant/preemergence herbicides along with a tank mix partner postemergence. He recommends using herbicides pre like Authority Assist, Sonic, or Valor, followed by tank mixes of Flexstar, Flexstar GT or Cobra postemergence. "This will be a strong combative tool in the fight to reduce financial losses from glyphosate resistant weeds in soybeans," he says.