Wheat growers need help in assessing resistant weeds
In the Northern Plains, recently noted resistant weeds include ACCase-resistant green foxtail and ALS-resistant kochia. “We’ve also been trying to manage and control ACCase-and ALS-resistant wild oat biotypes for several years now, and that’s the major concern today,” said Kirk Howatt, Ph.D., associate professor at North Dakota State University. “In terms of broadleaf weeds, the control we achieve is typically strong with products we currently have available for use in cereals, but we do have weeds like kochia that are becoming increasingly tolerant to various modes of action. We’re also seeing glyphosate resistance with ragweed and water hemp,” Howatt explained.
Howatt encourages keeping a close eye on weed species becoming increasingly tolerant to herbicides that once offered complete control, as well as evaluating a long-term strategy for greater return on investments over several years. “Preventive management solutions, or ‘the Cadillac treatment’ may cost more in the short-term,” he said, “but they help set the stage for a long-term gain and guard against potentially expensive problems before they occur.”
Start with a Competitive Crop
When problem weeds cannot be controlled by a previously effective herbicide, there is enhanced weed-crop competition for water, nutrients and light. “Weed scientists recommend growers use all the tools available to them in the most effective way possible,” Thill said. “The number one method of weed control is growing a competitive crop. If you begin with that, and you do all the right things to ensure the crop is aggressive and strong, weed control will be simpler to manage,” he added.
“Select the right varieties, plant at the right time and at the right depth, use the proper seeding rate and adjust for correct spacing; these agronomic practices can be followed by all growers to get the crop off to a healthy start,” he said. In addition, seed treatment insecticide and seed treatment fungicide help ensure optimum root health, stand establishment, increased vigor, maximum yield potential, as well as offer protection against the trifecta of yield-robing diseases Rhizoctonia, Pythium and Fusarium in cereals.
Alternate, alternate, alternate
Over-reliance on the same herbicide mode of action is one of the key contributors to the growing problem. Experts say there is no substitute for alternating herbicides with different modes of action and chemical classes in the fight against resistance. “Yields can increase significantly with proper herbicide management,” said Howatt. “It’s unreliable and not recommended to cut labeled herbicide rates,” he added. For most effective management, be sure to use sequential applications and/or tank mixtures of herbicides with different modes of action; apply herbicides at the full label rate and at the proper growth stage; extend the range of available herbicides by employing a diverse crop/fallow rotation; and prevent weed escapes from producing seed by controlling weeds early on.