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An aerial view of a cornfield shows yellow circular spots representing hail damage.
Weed evolve resistance to herbicides
By Jeff Dankert NewsTribune Reporter
In the battle to grow one or two crop plants on millions of Illinois acres, farmers have several weapons and most of them are chemical. Relying too heavily on one weapon can give the enemy a strategy for counterattack. This has become the case with over-reliance on the weed-killer glyphosate. A few decades and millions of acres gave weeds the time and space to evolve resistance. “What we’re trying to recommend is that farmers consider a new arsenal they have available and make sure they have different weapons with different modes of action against the weeds,” said Dennis Bowman, University of Illinois Extension crop systems educator. The glyphosate rut is mostly due to Roundup-Ready corn and soybeans by Monsanto. These crops’ genetics are engineered to survive sprayings of Monsanto’s glyphosphate product, Roundup, leaving only the weeds to die. But repeated use selected for weeds that are glyphosate-resistant. “It was easy to go out and do that over and over and over,” said Lambert Leonard, who grows and corn and soybeans in La Salle and Bureau counties. “With Roundup-Ready crops the Roundup was accelerating the whole problem,” he said. “The main culprit is overuse of one herbicide.” Aaron Hager, extension weed specialist, wrote this spring that “continual evolution of herbicide-resistant weeds” is a daunting problem in agriculture. Leading the survival-of-the-fittest race in Illinois is waterhemp, Bowman said. “We’ve seen resistance to glyphosphate, mostly tall waterhemp and marestail coming up from the south but we’re seeing it all around the state,” Bowman said. Increasing volumes of the same herbicide only worsens the problem. Every spraying of glyphosphate provides weeds “the opportunity for resistance,” Bowman said. Switching herbicides, the timing of spraying and other factors are recommended. Spraying prior to emergence and rotating crops year to year might work, he said. “One of the interests that we have right now is the use of cover crops to keep the ground protected and shaded and sometimes the different species of cover crops seem to have an inhibiting effect (on weeds),” Bowman said. Mechanical cultivation, tillage practices and improved planting dates also can work, he said. Bill Otterbach farms east of Mendota and has seen little sign of resistance. “I’m 100-percent rotated so that may or may not make a difference in weed control,” he said. “I use a different chemical for each crop so I guess I haven’t seen it.” A farmer near Tonica said horseweed shows some resistance but that “Roundup and other chemicals are taking care of it.” Leonard sees marestail survive spraying on his cropland in La Salle and Bureau counties. “What I’m starting to notice is the marestail, it’s not dying with Roundup and 2,4-D,” he said. The weed curls over but comes back, he said. So, Leonard is spraying before planting. “Using Roundup later, it’s not doing a really good job on that marestail,” Leonard said. “That’s a sign we’re developing a problem. Time it differently but also use other herbicides with it. Don’t just use that one herbicide.” So far, Leonard has not seen rampant patches of resistant weeds. “We are starting to see some kind of ragweed resistance,” he said. Of course, evolution applies to all organisms. “We have the same issue with insects as well,” Bowman said. “If we overuse it, Mother Nature will find a way to overcome our techniques.”
This year’s corn and soybean fields didn’t have far to go to beat last year’s drought-impacted row-crops. Area farmers reported good progress along with a few midsummer challenges. “It’s definitely better than last year,” said Lambert Leonard, who farms in La Salle and Bureau counties. Bill Otterbach near Mendota said harvest time will tell how his crop fared and by then he will know more about crop insurance coverage for hail damage. “I think I’m pretty good,” Otterbach said. “I took a shot of hail and it did quite extensive damage and it affected probably about a fourth of the corn crop. I’m guessing my yields are going to be down because of that. The good corn looks good and the bad looks horrible. I just don’t know where to put this crop at.” Otterbach surveys his crops by airplane and can see hail damage as yellow swaths, he said. Soybeans tolerated hail a little better but their growth is behind, Otterbach said. “If we get the rains in August we’ll have a normal to good crop on the beans,” he said. Rain for soybeans also was the hope of Lambert Leonard for his fields near Mendota, Earlville, Ladd and Spring Valley. “The soybeans are a little behind,” he said. “They got planted a little later than we liked. They could use a nice shower right now. My main concern right now is the soybeans. They’re behind. Soybeans can catch up. They appear to be short but short soybeans can still yield. They still need a drink of water right now.” Lambert scouted for Japanese beetles this week. “The Japanese beetles are eating the leaves but we have not started spraying them yet,” he said. “I project a lot of the corn in this area will get sprayed for that reason. We’ll just have to keep watching it, walking a lot of fields and monitoring the insect level.” A Tonica-area farmer reported the opposite, with soybeans doing better than corn due to timing of planting in a wet spring. Lambert said his corn looks good despite mistimed planting. “The corn looks very good with a rocky start from the beginning and we didn’t get it in as early as we liked to,” he said. “We planted the corn a little bit later but the corn looks very good in this area.” Farmers hope rain and cooler weather helps corn pollination, which is imminent. Fifty percent of corn and 61 percent of soybeans were in good condition across the state, according to this week’s Illinois weather and crop report from the U.S. Department of Agriculture. But even without a drought this year, the state’s corn and soybeans were behind last year’s crop on several points. Corn and soybeans were shorter than at this time last year. Corn silking and soybean blooming also is behind last year’s crops, according to the report.
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