The Residual Comeback
February 23, 2009 Across the weed spectrum in the Southeast and Mid-South, there is no doubt that glyphosate- and ALS-resistant marestail and palmer amaranth are on most every cotton grower’s anxiety list.
“To say (resistance) has changed our thinking and our way of life is an understatement,” says Dr. Alan York, North Carolina Extension weed specialist. And because of that, Extension and University recommendations are calling for a return to residual herbicides.
“We are at the point where we are going to have to fight this with residuals,” says Dr. Trey Koger at the Delta Research and Extension Center in Stoneville, MS. “We have the residuals to help us combat the problem, and they are older chemistries. Yes, they are an added expense, but if we are committed to growing cotton, we cannot rely on glyphosate, glyphosate, glyphosate.”
Postharvest Residuals
Some of the pre- and at-planting residual products coming back into vogue are metolachlor, fluometuron, prometryn, diuron and the “yellow” herbicides.
But there are also residual herbicides — some with contact activity, as well — that can be applied from postharvest through winter. One of those with both residual and contact activity is Envoke from Syngenta.
Envoke is an ALS inhibitor in the sulfonylurea class of herbicides. Another with both is Clarity — a dicamba-based herbicide from BASF. Valor — a PPO inhibitor from Valent — offers residual control.
James Holloway, Syngenta’s Senior R&D Scientist, says controlling weeds at emergence in the winter pays dividends in the spring. “If we don’t start when those (weed) seedlings emerge, we’re fighting a losing battle, and it will go into the following season. The quicker we get on them, the better off we are. If we have a clean seed bed as we go into the winter months, we have a better chance of having one going into the spring planting season.”
Envoke has a 90-day preplant restriction for cotton, so it is recommended from postharvest through winter. Clarity can be used in the initial burndown application, and again later if there is a another flush of weeds. Valor can be applied postharvest until layby, but a hooded sprayer is required in layby applications.
Although glyphosate resistance is the most common, growers should understand that there is also ALS resistance and take the appropriate steps where it is found. “As with a lot of the ALS herbicides, we are still seeing fantastic activity on many weeds,” says Syngenta product manage Duane Martin. “But growers need to be aware that we do have ALS resistance. They are going to have to plan for that and make sure they put the right herbicides in a tank mix to control resistant marestail.”
Billy Beegle, whose consulting service includes west Tennessee, the Missouri Bootheel and northern Arkansas, began looking at Envoke in 2006 in two test plots – one in a tank mix with Clarity, and another in a tank mix with 2,4-D. “I was very pleased with both of them,” he says. “We got 99% control of marestail – which is what we were going for – but it left poa anna out there, which is good. We need a little ground cover on these fields, either for wind in Missouri, or for erosion control in Tennessee.”
“We have some good burndown materials, such as 2,4-D or Clarity,” York says. “But what do you do for the next flush of weeds we are going to have? Valor can be part of our burndown program because it gives residual control.”
Captions:
Resistant marestail
Palmer amaranth
Billy Beegle
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