Combine tools to fight herbicide-resistant weeds in corn
Sweet-corn growers are gaining new tools to supplement triazine herbicides as herbicide-resistant weeds become more common.
New this year is the post-emergent herbicide Impact (topramazone) from Amvac Chemical Corp. of Newport Beach, Calif. It is not registered in California.
Two other herbicides are nearing registration, says Chris Boerboom, Extension weed scientist at the University of Wisconsin in Madison.
Triazine resistance in such broadleaf weeds as lambsquarter, kochia and waterhemp has been an ongoing concern for the past 20 years, says Aaron Hager, Extension weed control specialist at the University of Illinois, Urbana-Champaign in Urbana.
While not as widespread as resistance to ALS inhibitors, triazine resistance is more of a challenge to sweet-corn growers because their herbicide options are limited, he says.
“We’re faced with that every year,” says Dan Hinkle, owner of Hinkle Produce in Cissna Park, Ill.
Resistant weeds in his 1,000 acres of sweet corn reduce the efficacy of Bicep Magnum (atrazine and s-metolachlor), a versatile herbicide from Syngenta Crop Protection of Greensboro, N.C., that doesn’t damage the crop.
Weeds hit the bottom line
Weeds are a major problem in sweet corn, and most fields are treated with pre-emergent herbicides containing atrazine, says Marty Williams, a weed ecologist with the U.S. Department of Agriculture’s Agricultural Research Service in Urbana.
Weed competition affects the number of ears produced per acre as well as kernel fill and other quality measures, says John Masiunas, University of Illinois, Urbana-Champaign associate professor of vegetable crop weed management.
Weeds compete for water and nutrients, concerns not limited to dry years as growers fight to cut input costs, Hinkle says.
Weeds also shelter pests and restrict pesticide application coverage, Masiunas says.
Overcoming crop injury from post-emergent herbicides is a priority, Williams says.
Hybrid sweet corn selection affects how well a crop tolerates weeds, he says. GH2547, for example, produces a canopy that shades out weeds more efficiently than the shorter Spirit hybrid.
Williams’ research includes identifying specific traits that make some hybrids more weed-tolerant.
Timing is everything
Adjusting planting schedules, when possible, may overcome some weed problems, Williams says.
Yield losses from lambsquarter and foxtail are more significant in early plantings; early corn often needs more intensive management over a longer period to keep weeds in check.