Herbicide-resistant weeds are a top threat to corn and soybean yield potential — and the future of crop production.

“Because weed resistance is naturally occurring, it’s a myth that we can create a silver bullet that’s impermeable to resistance pressure,” says Todd Spivey, market development specialist for Corteva Agriscience. “We must protect our strongest and most reliable products by using multiple measures that will help prevent the selection and buildup of resistant weeds.”

Spivey offers six ways to avoid the development of weed resistance on your operation:

1. Know the signs. Identifying weed resistance is not a reflection of poor management. It can, however, equip you with the knowledge and resources to tackle difficult weeds moving forward. The best time to diagnose possible resistance is immediately after an herbicide application, Spivey says.

Find an area where weed density is sparse, so you are sure all weeds received equal amounts of herbicide. A spot that has all the same weed species is ideal. Did you find some weeds controlled, some looking like they haven’t been sprayed and some lingering in between? This is usually how weed resistance starts to express itself.

2. Scout fields regularly. “Before an herbicide application is ever made, you should know what weeds are present, what size they are and how many there are,” Spivey says. “Continuous scouting before and after applications is the only way to determine the effectiveness of any weed management program.”

Spivey recommends keeping a weed journal to note which weed species are present and in what proportion. Doing this on a regular basis will help you notice shifts on your farm. “Having this information in writing is important, as none of us have the memory that we think we do,” Spivey says.

Scouting trips after herbicide applications will help gauge herbicide efficacy. The information from these immediate scouting visits, coupled with regular weed journal notes, will help develop a baseline for any changes that occur over time.

If misses or failures occur, it’s important to correct the lack of control and determine the cause as soon as possible.

3. Take immediate action when resistance is suspected. “If resistance is suspected, you’ll want to control the weed in question with a labeled herbicide that includes another mode of action, or with nonchemical weed control,” Spivey says. “This is vital to prevent the weeds from going to seed.” 

4. Rotate herbicide modes of action. Always use multiple effective modes of action with every herbicide application. “This can be accomplished with a program approach that includes two- and three-way premixes or by tank-mixing multiple products,” Spivey says. “Effective is the key word here. Including glyphosate in a tank-mix when trying to manage glyphosate-resistant weeds does not count as an effective mode of action.”

5. Rotate crops. Rotating crops allows for additional herbicides and modes of action to be used. “For example, growers can take advantage of the HPPD-inhibiting products for broadleaf control in corn and utilize the ACCase inhibitors for grass control in soybeans,” Spivey says.

6. Advocate for weed resistance prevention strategies. Herbicide resistance issues are not isolated to one farm. Ditches, leased and traded land, and used and traded equipment are all sources of herbicide-resistant weed seed, so the prevention of herbicide resistance must be a concerted effort from all parties. 

“Our ability to provide new active ingredients to the market is outpaced by growing weed resistance pressure,” Spivey says. “Because of this, it is vital that growers implement strategies now to prevent weed resistance versus waiting to address the issue in the future.”

Source: Corteva Agriscience