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Three hot topics for 2022 weed control

Prioritize herbicide supplies, watch Dicamba movement, and hopping off the herbicide treadmill.

Heading into the 2022 growing season, farmers are faced with a host of worrisome challenges for weed control options. Shortages of herbicide products – and record high prices for what is available – plus the ever-present prospect of off-target dicamba movement are among those that vex Kevin Bradley, Extension weed specialist at the University of Missouri.

Here are his hot topics to watch for in 2022.

1. Herbicide Shortages/Supply Chain Issues

“Much has been said and written about the potential shortages of glyphosate and glufosinate that are expected in 2022. After talking about this with growers and retailers around the state and after my (admittedly abbreviated) winter meeting season, I'm also not sure who will have a shortage of these herbicides in 2022, and who won't,” says Bradley. “I've heard everything from, ‘we don't have any problem getting glyphosate/glufosinate in this area’ to ‘we will be very limited in this area’.”

Kevin Bradley, University of Missouri weed specialist
Kevin Bradley
Growers who anticipate being unable to source enough glyphosate or glufosinate for 2022 are advised to determine the best way to use the herbicide(s) that you do have available for the good of your overall weed management program.

“Target your worst weeds with the herbicides that give you the best opportunity for success first and take every opportunity to make the most out of the herbicide that you intend to spray.” Bradley advises.

In other words, proper herbicide timing will be as important this year as ever (to eliminate the need for any potential re-sprays). Also, use the correct nozzles, adjuvants, gallons per acre and other best management practices.

“In corn, we still have a variety of effective post-emergence weed management options and herbicide groups that do not involve glyphosate or glufosinate. These would include the group 4 (2,4-D, dicamba, etc.), group 27 (Callisto, Impact, Laudis, Shieldex, etc.), and group 2 (Resolve, Steadfast, etc.) herbicides,” Bradley continues. “In other words, you can probably get by easiest in corn without glyphosate or glufosinate.” 

For soybeans, growers must rely on effective residual herbicides pre- and post-emergence as much as possible. Waterhemp and Palmer amaranth challenges should have taught farmers the importance of these practices.

“Also because of our problems with these resistant weed species, soybean is a crop where a potential shortage of glufosinate might hurt the most. If used correctly, glufosinate is still an herbicide that works on the pigweed species in most Missouri soybean fields,” Bradley says.

He recommends saving glufosinate for post-emergence use in Enlist soybean (preferably with Enlist One), or for post-emergence use in Liberty Link, Liberty Link GT27, or XtendFlex soybean.

To terminate cover crops, glyphosate or glyphosate mixtures are most often the most effective and most consistent option.

“If I had to ‘save’ glyphosate for use this season, I'd want to try to keep some of it for cover crop termination,” he says. “But if you cannot find glyphosate and have to switch to another non-selective herbicide, our data indicates that tank mixes that include paraquat (Gramoxone) may be the next best alternative.” Another option for the control of grass cover crops would be the application of a group 1 herbicide like clethodim (Select Max, Arrow, etc.) or others, but obviously these herbicides would not provide any control of legume or broadleaf weed species.

2. Off-target Dicamba movement 

“As much as I wish it weren't the case, unfortunately the issues with off-target movement of dicamba have not ended and each season we have continued to see dicamba move off-target and injure neighboring soybean fields and other sensitive plant species,” Bradley says.

Mizzou research shows there is quite a bit of secondary movement that occurs after the sprayer has left the field, and it is this secondary movement that is outside of the applicator's control.

For growers who intend to plant XtendFlex soybean and spray one of the approved dicamba products this season, pay close attention to the label requirements and environmental conditions expected prior to and after the application has been made. If conditions are not optimum for a dicamba application, post-emergence applications of glufosinate are labeled for use in XtendFlex soybean.

3. Too much reliance on herbicides

Bradley says herbicide resistance remains a massive challenge for farmers. For example: waterhemp is now resistant to seven different herbicide site of action groups (2, 4, 5, 9, 14, 15, and 27). Palmer amaranth is resistant to nine (2, 3, 4, 5, 9, 10, 14, 15, 27).

Bradley notes that Tennessee weed specialist Larry Steckel and Aaron Hager at the University of Illinois each confirmed the presence of dicamba-resistant waterhemp populations in their respective states.

“I’m not aware of any official dicamba-resistant populations in Missouri, but we have observed a high degree of variability in the control of Missouri waterhemp populations with this herbicide in our screening efforts over the past several seasons,” he says. “All of this is just simply to say, our growers as well as our entire industry needs to be more open to an integrated approach to weed management that considers all available options, not just herbicides.”

The treadmill approach to weed management with herbicides, where the industry promotes one mode of action until it breaks, and then switch to another until that one breaks, and so on, isn’t sustainable.

“We must start including other preventative, cultural and/or mechanical weed management practices into our programs before it's too late,” he says.

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