Identifying Signs of and Managing Weed Resistance
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Farmers are unquestionably the world’s most unheralded front-line environmental stewards. With nearly 96% of U.S. farms family-owned, those families work their entire lives to sustain their farming heritage and leave the land better than they found it so the next generation can continue the family's farming legacy.
Although farmers face many threats to that legacy, and their corresponding profitability each season, the development and management of weed resistance is one that continues to expand across farming’s global landscape.
“Resistance is prevalent and widespread,” says Jason Gibson, market development specialist, Corteva Agriscience, covering Nebraska. “In addition to glyphosate, which developed resistance quicker than many anticipated, today we see HPPD resistance near seed production locations and resistance of dicamba to Palmer amaranth. Despite the progression of that resistance, these chemistries still play an important role in weed control.”
Gibson explains that most of the resistance famers were dealing with until around 2008 was target site resistance — which was easy to see because there would be a few surviving weeds among other weeds that were controlled by the herbicide application. The resistance farmers face today is nontarget site resistance, often described as creeping resistance. It is not obvious until one day it becomes a struggle to control most of the population within a field.
Spread, Identification and Management
The increasing spread of herbicide resistance remains a threat to crop quality and yield. It limits the number of solutions in a farmer's herbicide toolbox and, in many cases, increases input costs from additional applications for attempted control.
Weed resistance mobility is well-documented and may be spread by migrating wildlife, the use of the same equipment on different farms, as well as metabolically, which occurs when a plant breaks down the herbicide faster than the herbicide can affect the plant.
“The best advice you can give a farmer is to be proactive by controlling resistance before they see it,” Gibson says. “By applying a preemergence premix or tank mix with multiple effective sites of action, the number of weeds that will need to be controlled postemergence may be reduced – which is where the greatest challenge lies in managing resistance.”
Always advise your customers to send weed seed samples into a lab to confirm a suspected resistant weed. Correct identification is the first step to a tailored program approach weed control plan. Share this www.weedscience.org website with them as well and encourage your customers to use it to help recognize documented weed resistance in your specific region.
Once resistance is confirmed on a farm, a good scout who keeps accurate records can be invaluable to help monitor weed types and density over time. That information helps provide perspective on the effectiveness of any program approach to weed control.
“Think of a program approach the same way you would think of using a blueprint to build a house,” Gibson says. “Both help assemble the plan and lead to the desired outcome. A program approach would always include overlapping residuals.”
You should recommend using 4-Hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors preemergence in corn and protoporphyrinogen oxidase (PPO) inhibitors preemergence in soybeans. Doing so can be extremely helpful because these sites of action are less commonly used in consecutive seasons in the Midwest, where corn and soybean rotation is prominent. Both herbicide classes play an important role in managing amaranth species that include Palmer amaranth and waterhemp.
Corteva Agriscience has a robust portfolio of corn and soybean herbicides available, so you can help customers find the right mix for their operation. Consult your local Corteva representative or visit Corteva.us for more information.