It's been a “crazy year” for weeds, says Ken Smith, weed scientist for the University of Arkansas Cooperative Extension Service. He attributed this to unusual spring weather patterns.
It's nutsedge in soybeans that has him concerned. Nutsedge is flexing its muscle and showing why it's considered one of the Top 10 most troublesome weeds in Arkansas.
Smith and Bob Scott, another Extension weed scientist, say they're being bombarded with telephone calls about nutsedge.
“Soybeans seem to be infested with nutsedge,” Scott said. “Unfortunately, there's not a lot you can do. Roundup is weak on nutsedge. Pursuit is a good tank partner with Roundup, but it has a 40-month rotational interval to rice.” In other words, farmers have to wait 40 months until they can plant rice after using Pursuit in soybeans.
Scott said the statewide nutsedge problem is mostly related to rain.
“We've had all this rain, and we haven't been able to get our burndown herbicides out.” He said the result is that yellow nutsedge weeds get bigger and harder to control.
Smith and Scott said it's important to control nutsedge in rice this year even if the problem isn't severe. They said if farmers let the weeds go in rice this year, then rotate to soybeans next year, the weeds will reach competitive levels and be harder to control.
Smith said farmers are perplexed about what to do.
“They're asking about mixing Dual Magnum with Roundup postemergence, which is not labeled. Some are asking about Pursuit. Others are still wondering why nutsedge is getting worse when they're spraying two or three times with Roundup.
“Our best recommendation is to fight nutsedge hard in rice and then try to farm it or manage it in soybeans,” Smith said. “We have much more effective nutsedge tools in rice than beans, and farmers should take advantage of those tools to control nutsedge in rice.”
He said Dual Magnum pre followed by glyphosate (the active ingredient in Roundup) will help suppress nutsedge early and allow growers to manage the soybeans. However, the combination won't control nutsedge, and by the end of the year it may be worse than at the beginning. Still, he said, this is better than doing nothing.
Dual Magnum is not labeled for postemergence applications in soybeans as it is in cotton, Smith noted. This allows a long period of time between planting and harvest for the nutsedge to recover and multiply.
Smith said that Pursuit plus Roundup is effective in soybeans. Pursuit has the same active ingredient as Newpath. But, if it's used, it can't be followed the next year with regular rice. It can, however, be followed with Clearfield rice.
He said Permit is fairly effective on nutsedge in rice, and farmers still have time to apply it this year.
“It will not eliminate nutsedge, especially in a soybean rotation, but it'll knock the population back enough to allow Dual Magnum followed by Roundup to keep the population below competitive levels.”
Scott recommended that farmers use Permit to get good control in rice this year so that they can avoid a nutsedge problem in soybeans next year.
Smith noted that glyphosate alone will not consistently control nutsedge at regular use rates. He said the herbicide usually causes nutsedge to turn a slight to moderate yellow, then it turns back to green and continues to grow.
Lamar James is an Extension communications specialist with the University of Arkansas.