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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 crop injury may be necessary
“Sencor (mostly generic versions now) is also a good option we haven’t used much — not only for pigweed, but for horseweed and ryegrass. . There currently is no pigweed resistance to this material in the Mid-South. Boundary is a combination of Sencor/Dual and is a jam-up combination for these weeds.
“In many situations, some amount of crop injury will be something you will have to live with in order to get control of pigweed.”
Bond: “You can expect some injury from a residual herbicide. Some of these materials have been around forever — in the grand scheme of things, they’re antiques, but they work the same as they did decades ago, and you’re still going to get injury. You’ve got to seek a balance between some herbicide injury loss and major loss from resistant weed competition.”
Dodds: For the last 15 years, we’ve become accustomed to seeing a robustly-growing cotton crop with little or no injury; however, cotton can sustain some herbicide injury and still produce well.”
Eubank: “As we shift more to contact herbicides, it’s very important to have adequate coverage. You can’t apply these herbicides with AI nozzles, low water volume, and a high ground speed and get the coverage you need.
“If you’re going across the field at 20 mph, a lot of your smaller spray particles are being caught up in the vortex of wind and dust behind your sprayer and coverage isn’t as effective as it should be. If you miss control the first time around, there’s no coming back for a do-over.
“You need an orifice size that will put out the necessary volume of water for thorough coverage. I like 10 gallons minimum, preferably 15 and no more than 10 mph.”