Ag department updates guidelines for acetochlor
By Heather Thorstensen
hthorstensen@agrinews.com
Date Modified: 05/19/2010 3:36 PM
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ST. PAUL— The Minnesota Department of Agriculture has updated their best-management practices for use of acetochlor.
The herbicide is used to control grassy weeds in Minnesota corn fields. In 2010, some product labels were expanded so it could be used on soybeans. Depending on specific product labels, acetochlor is registered in the state for use on field corn, popcorn, production seed corn, silage corn, sweet corn and soybeans.
The best-management guidelines were originally developed in 2004 to protect surface and ground water while helping farmers get successful weed control. They are voluntary, except when they reference product label requirements.
The updates set specific minimum recommendations for the first time on how wide filter strips should be — 30 feet —and how far acetochlor application should be kept from water, 66 feet. The ag department thought setting specifics would make the guidelines easier to follow, according to Ron Struss, MDA's pesticide best management practice coordinator.Farmers should consult with Soil and Water Conservation District staff or Natural Resources Conservation Service staff for help designing filter strips most appropriate to their land, and to use as wide of a vegetation strip as practical for their site, the guidelines say.
The updates also promote lower pre-emergence acetochlor rates if the farm will use post-emergence weed control in a herbicide-tolerant crop system.
"Many farmers are depending on a post-emergence herbicide program, mostly in glyphosate, and in that case, the pre-emergence application of acetochlor doesn't have to last the whole season," said Struss. "...When the original best-management practices were written, these things weren't common place."
The recommendations now give the option to rotate acetochlor applications with other herbicides in the acetamide family. This includes metolachlor, dimethenamid and flufenacet. Previously, the recommendation was to rotate with products outside this group to slow the development of weed resistance.
"The challenge with acetochlor is there weren't that many good grass herbicides for corn outside the acetamide family," said Struss.
This is a safe compromise, he said, because there hasn't been much evidence of weed resistance to acetamide herbicides. Rotating herbicides also allows less of any one chemical to enter water systems.
Precision application technology has been included in the best-management practices to avoid needless application of herbicide.
"Since 2004, the use of these technologies have caught on tremendously so we wanted to reflect that in the updates," Struss said.
The guidelines were revised this year is to take a pro-active approach to the state's water quality impairments. Acetochlor is the only herbicide listed as a reason for impaired waters on the state's impaired waters list, Struss said. The herbicide is credited for impairments in south-central Minnesota's Le Sueur River and Little Beauford Ditch.
It's important farmers follow the guidelines to avoid regulations that could be added to herbicide use, Struss said.
"If best-management practices are not being effective, we would look to the next step — putting restrictions on specific pesticides as needed —but we're not at that point," he said. "That's why it's important to use the best-management practices, because it keeps us in a pro-active, voluntary approach."
General best-management practices exist for all agricultural herbicides and there are specific guidelines for acetochlor, alachlor, atrazine, metolachlor and metribuzin. These chemicals have been found frequently in ground water, but at low levels, and the levels are increasingly lower. It's hoped the guidelines help that trend continue.
Acetochlor and atrazine have been detected frequently in surface water at concentration levels that approach or exceed water quality standards.
New guidance materials with the acetochlor updates have been mailed to pesticide dealers and applicators, crop consultants, Extension educators, pesticide company representatives, soil and water conservation district staff and watershed district staff.
MDA revised the guidelines based on suggestions from their staff, manufacturers of acetochlor, crop producers, University of Minnesota staff, and state and federal agencies that work with crop production and water protection.