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Coping with herbicide-resistant weeds, after decades of the easy, sure control afforded by glyphosate (Roundup), will require a multi-pronged approach, Mississippi growers were told at the 2011 Delta Ag Expo. As glyphosate-resistant pigweed (Palmer amaranth) spreads in the Mid-South, and resistant Italian ryegrass continues to be documented, producers will need to include alternate chemistries — many of which are decades-old active ingredients — in their weed control programs, a panel of specialists noted.
Some grower attitudes 'a recipe for disaster'
“Unfortunately, we have some growers who take the attitude, ‘I’m going to keep spraying with Roundup until it doesn’t work any more.’ That’s a recipe for disaster.
“Even if you don’t have pigweed, but your neighbor does, it’s likely going to spread to your fields. The seed will stick to equipment, or to you, like white on rice. A lot of spread is by equipment movement. If you use a custom harvester, make sure they clean their equipment thoroughly before coming to your fields.”
Dodds: “There was a grower in the Mississippi hills who bought a sprayer in Arkansas that has a tremendous amount of pigweed seeds in many crevices of the machine. Had he not cleaned it before putting it in his fields, he’d have spread those seeds everywhere. Be extremely careful about buying equipment in areas where there is resistant pigweed — it could be a very costly purchase.”
Bond: “Equipment movement is a major way ryegrass is spread. Landplanes do an unbelievably effective job of spreading the seed. It is also easily spread by combines.
“Ryegrass doesn’t spread as fast as pigweed and it’s usually worse in field margins, or along roads, so you have an opportunity to control it in those areas and limit it spreading to your fields.
“We had many calls last year about fields that were infested with pigweed where they’d never had it before. But it’s mind-boggling how big these plants can grow, how much seed a large pigweed plant can produce, and how easily those seeds can spread.
“When I was in graduate school, we grew a pigweed that was 12 feet tall and weighed 45 pounds. In Arkansas, researchers counted 1.7 million seeds on a single plant. Even if you get 96 percent or 97 percent control, with that kind of seed numbers you can get behind the math curve pretty quickly.