Fargo News

Dicamba resistance confirmed: Waterhemp poses new threat to North Dakota

Fargo, North Dakota – Waterhemp emergence in the Fargo area during mid-May indicates that farmers in eastern North Dakota will face another challenging year in combating this persistent weed and maintaining clean fields.

In the previous year, resistance to PPO-inhibiting (Group 14) herbicides was confirmed in waterhemp populations across seven counties in North Dakota. Further greenhouse testing this winter revealed Group 14-resistant waterhemp in an additional county, Benson.

However, the significant development, as highlighted by Joe Ikley, NDSU Extension weed specialist, is the confirmation of the first known waterhemp resistance to dicamba in North Dakota. A comprehensive dose response analysis on a population from Traill County confirmed this resistance, while samples from Griggs and Ramsey counties displayed survival at 3x rates of dicamba, demonstrating a similar phenotypic response to the Traill County population.

Ikley stated, “This population we’ve been working with is the first case in our state where we’ve confirmed resistance. Back in 2019, there were complaints about dicamba’s performance on waterhemp in southeastern North Dakota, but we couldn’t confirm it. However, in the past year, we had a population where we could. So, for about four years, we’ve had concerns, but as of the 2022 field season, we have dicamba resistance that we have to address.”

Waterhemp first appeared in the southeastern part of the Red River Valley in the early 1990s, and over the past decade, its prevalence has steadily increased. Presently, waterhemp can be found in the eastern half of North Dakota, predominantly in the southeastern corner. The weed’s encroachment into the Red River Valley has made it one of the top three most problematic weeds in the region, primarily due to herbicide resistance.

Waterhemp has already demonstrated resistance to glyphosate and Group 2 herbicides, and more recently, resistance has been confirmed with Group 14 herbicides and now dicamba.

“It’s a weed that produces a significant amount of seed, and with the challenges of herbicide resistance, it’s becoming increasingly difficult to keep fields free of waterhemp throughout the growing season, especially in crops like soybeans, dry edible beans, and sugarbeets,” explained Ikley.

The confirmation of dicamba resistance poses a substantial challenge for growers who rely on the XtendFlex soybean platform, as dicamba usage is one of the primary reasons for choosing this platform.

“It’s a significant issue because we’ve already lost glyphosate, so we’ve been relying on glufosinate (Liberty) and similar soybean systems. We could rotate to Enlist, as it is still effective, but this resistance will also affect other crops,” noted Ikley.

He further added, “For corn, we rely on dicamba-based herbicides like Status for post-emergence applications to control broadleaf weeds. With the loss of this option, it will be problematic in other crops where dicamba is used.”

As farmers work diligently to plant their crops this spring, Ikley emphasizes the importance of timely weed control to mitigate resistance.

“With another shortened planting season ahead of us and favorable conditions of warmth and ample moisture, weeds are growing rapidly. One of the most effective ways to prevent herbicide resistance is to spray weeds when they are small, typically around 3 inches or smaller, preferably 2 inches. If we can apply post-emergence herbicides when the weeds are small, we can achieve better control and stay ahead of resistance development,” concluded Ikley.

Mitch Havens

Mitch holds a distinguished position as a foremost authority at Fargo News Now. Drawing upon his prior expertise garnered from renowned publications such as CNN and Time, our ambitions extend beyond merely serving the local community, as we also aspire to make a national impact in the realm of journalism.

Comments are closed.