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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.
Best control obtained when weeds are small
“And it’s critical that these alternative chemistries, such as Ignite and Flexstar, be applied to pigweeds when they’re 2 inches to 3 inches high, no more than 4 inches. The days are gone when you’re going to get control of large pigweeds with any herbicide.
“There is no residual herbicide you can put out in the fall or late winter that will carry over to provide control the following season. It’s important that you start with a clean field in the spring — but you may still have to come back later with other materials to control escapes. Metribuzin is still a good burndown material that offers some residual control.”
Dodds: “The move by producers to Roundup Ready is like a gerbil on a revolving wheel — it’s hard to get off. Once growers got on the wheel, they felt they couldn’t afford the cost and/or didn’t need tillage and other measures because of the technology fees they were having to pay.
“We’ve never quit making recommendations for tillage, but production economics and farm size have led many growers away from it. In Mississippi, tillage is still a good option as part of a pigweed and ryegrass control program. It’s not a solution in every situation, but we need to keep it in mind as an option.
“We have a limited number of modes of action in herbicides and we need to do all we can to effectively use them and preserve them. In many cases, we’re recycling herbicides we’ve had for 50 years or more. New chemistries don’t come along very often — I can count on one hand those I’ve seen in 10 or 12 years.”
Bond: “Unfortunately, we’re too often in a reactive mode rather than proactive. Crop rotation, use of alternate chemistries, and tillage are long term, proactive measures in dealing with weed resistance.”