SIKESTON -- Farmers who aren't already rotating crops and herbicide chemistry should do so this spring, experts say.
The recent discovery of waterhemp, or pigweed, in two fields in northeast Missouri has caused agriculture officials statewide to wonder how long it will be before their weeds become resistant to glyphosate -- the key ingredient used in Monsanto's Roundup Ready seeds.
In Missouri, 100 percent of cotton, 95 percent soybeans and 20 percent of corn are Monsanto's Roundup Ready.
"This is a situation to watch carefully," said Andy Kendig, weed scientist for the University at Missouri Delta Center in Portageville. "There are a few herbicide-resistant weeds here and there in the United States."
In Southeast Missouri one weed developing herbicide resistance is horseweed. What's noteworthy about horseweed's resistance to glyphosate, Kendig said, is the fact it's spread about halfway across the United States in two years' time.
But Southeast Missouri farmers shouldn't panic, Kendig said.
"Our growers in Southeast Missouri are some of the best around. They are aware of the situation and are taking steps to prevent it," Kendig said.
When the Roundup Ready system came along, it reduced input costs for farmers, was a big help with simplicity and convenience and it improved weed control, he said.
"Monsanto always made the point glyphosate herbicide was not especially prone to developing resistance. In the 1990s cocklebur and pigweed became resistant to ALS (acetolactate synthase) herbicides, and we knew those herbicides were prone to develop resistance. And now we're seeing some resistant species show up with glyphosate," Kendig said.
It's not that farmers have been misusing the product that's caused the resistance, Kendig said. Rather it's the widespread, repeated use of a herbicide that is leading to some sporadic occurrences of resistance, he said.
"Farmers have planted a lot of Roundup Ready crops and are using a lot of glyphosate," Kendig said. "And it doesn't matter if you're talking about weed control or antibiotics. If you use one thing repeatedly, it can result in resistance."
Anthony Ohmes, agronomist for Mississippi County University Extension in Charleston, said there were more weed escapes (when a cultivated plant runs wild) than normally were seen in the area this year, but that doesn't mean they're resistant.
"It could be due to the extremely dry weather when applications were applied because the seeds are less responsive to the chemistry when it's dry," Ohmes said about the increased number of escapes.
Rotating crops in fields as well as rotating chemistry -- not rotating a Roundup Ready gene but adding some extra chemistry -- will help with prevention, Ohmes said.
Adding extra herbicide chemistry can increase production costs in a lot of cases, Kendig pointed out. A farmer's top three issues tend to be low commodity prices, high input prices and the availability of labor, he said.
"Prices for cotton, rice, corn and beans are as cheap as they've ever been in history," Kendig said. "Fertilizer and diesel fuel, are at all-time highs. Farmers aren't looking for increased weed control costs."
Paying attention to weeds in individual fields is important, Kendig said. If weeds that should have been controlled and for some unknown reason are not dying, that could be an indication of resistance, he said.
"Farmers should be aware that there are some resistance issues and there are other modes of action available to help control the issues we're dealing with now," Ohmes said.
But the fact is horseweed changed and became herbicide-resistant, Kendig said.
"The sky isn't falling," Kendig said. "And the world isn't coming to an end. Everyone wondered when this would happen. And now that it has, growers are making adjustments to their practices."