Revisit Older Herbicide Chemistries to Fight Weed Resistance

Revisit Older Herbicide Chemistries to Fight Weed Resistance

That may have to be one of the options as a result of weeds developing resistance to glyphosate.

There is currently no "silver bullet" to fix herbicide resistance issues, and producers shouldn't hold their breath waiting for one to be developed. That's the word from Leo Charvat, BASF biology area development manager at Lincoln and Beaver Crossing, who spoke to more than 200 producers at the recent herbicide resistance weed management field day in David City, sponsored by University of Nebraska Extension, Nebraska Soybean Board and several corporate sponsors.

NO SILVER BULLET: BASF researcher, Leo Charvat, told farmers that there is no silver bullet to help overcome weed herbicide resistance issues.

"All the former chemistries are being revisited" as a result of several weeds developing glyphosate resistance in recent years, Charvat said. Monsanto is working on an advanced technology known as "BioDirect," which would work in combination with glyphosate in controlling resistant weed species so they would again be susceptible. However, this technology is more than nine years away from being field ready. "We don't know for sure if it will ever be used," he said.

Producers need to look at best management practices they have been using for 20 or 30 years, said Charvat. "You will need to hit all of the chemistries, using best practices to address specific problems. This involves everything you do in production, he said.

"It involves how you apply herbicides, so we can sustain the chemistries that we have now and not put pressure to cause further resistance," Charvat said. "We need to bring to a standstill the increase in glyphosate resistance."

He suggested choosing up to three different modes of action for burndown herbicides and at least two different modes for foliar applications. It is best to choose herbicides that will overlap coverage on specific problem weed species like ragweed, waterhemp and kochia.

"We have to look at putting the full rate on," he said. Tank mixes should be developed around herbicides that have been used over the past 40 to 50 years that do not have a high rate of resistance to them. "If you use one mode of action year after year, you are going to have problems," Charvat said.

Timing of herbicide applications is another key to destroying weeds when they are most vulnerable, whether it is a pre-emergence or post-emergence application. "This might mean fall applications or spraying in late February or early March if the conditions are right," Charvat said. "Weeds must be small and the applications must come during a certain period to remove the weeds."

He said that other practices like paying attention to the nozzle size on the sprayer, using the correct amount of water and finding the best additives will help raise the effectiveness of herbicides.

"I don't think everyone is dealing with weed resistance right now, but this is nothing new," says Greg Kruger, UNL Extension cropping systems specialist. "Anything we do to control weeds will result in resistance." Glyphosate has worked so effectively over the past 15 years that we haven't had to utilize older chemistries, Kruger says. Now, producers have to look at chemistries and practices, including cover crops and tillage under some circumstances, to help control difficult weeds.

"We have to keep in mind that on the agronomic side, we are controlling weeds to mitigate yield loss," Kruger says. Ultimately, we have to find stewardship strategies that will maintain our chemistries, work into our overall cropping systems and protect our bottom line, he says.

For more information on weed resistance issues, contact Kruger at 308-696-6715.

TAGS: USDA Soybean
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