‘Huge’ increase in resistant weeds
North Dakota State University agronomists are receiving many phone calls and email messages about suspected herbicide-resistant weeds this summer.
“The biggest concern at this time is the highly suspected herbicide-resistant kochia populations in North Dakota and the Red River Valley,” says Jeff Stachler, NDSU and University of Minnesota Extension agronomist.
“It appears that glyphosate (Roundup)[Group 9]-resistant and fluroxypyr (Starane)[Group 4]-resistant kochia may be present at some frequency in 30% to 50% of all fields in the James River, Sheyenne River and Devils Lake watersheds in North Dakota. This is a huge change from last year when we knew of only three fields in this area having glyphosate- and fluroxypyr-resistant kochia.”
• Herbicide-resistant weed populations increase significantly.
• Resistant kochia may be present in 30% to 50% of fields.
• Removing resistant weeds by hand may be the only defense.
It is possible that fluroxypyr-resistant kochia is present in 5% to 10% of wheat fields in the Red River Valley, Stachler says.
NDSU has received information that there may be a field of glyphosate-resistant kochia in the Red River Valley in Richland County, N.D. This is the only known field in the Red River Valley at this time.
Additional reports of herbicide-resistant weeds include:
• an increase in the presence of common ragweed resistant to ALS (FirstRate, Pursuit, Raptor and other similar products)[Group 2]-inhibiting herbicides in North Dakota
• a suspected resistance in Mahnomen County, Minn., of common ragweed to PPO (Flexstar and Cobra)[Group 14]- and ALS-inhibiting herbicides
• continued spread of glyphosate-resistant common ragweed in Minnesota and North Dakota
• continued spread of glyphosate-resistant waterhemp in Minnesota and North Dakota (likely as far west in southern North Dakota as Highway 1)
• continued increase in glyphosate-resistant giant ragweed in southern Minnesota
• a slight increase in the frequency of wild oat and foxtail (pigeongrass) species resistant to ACCase (Assure II, Axial, Puma, Select and others)[Group 1]- and ALS-inhibiting herbicides
“This frequency of herbicide-resistant weeds is quite alarming,” Stachler says. “With the likelihood of no new herbicide mechanisms [site/mode] of action to be released within the next 10 years, we must preserve the tools currently available.”
Letting a single herbicide-resistant plant go to seed can have a major impact. A single waterhemp plant that goes to seed this season may allow for the presence of 6.25 million plants two seasons later if management strategies are not drastically changed, Stachler says.
“The only means that I am aware of to effectively manage the resistant plants in a field is to remove them by hand or with row cultivation,” he says. “Getting back to removing resistant plants by hand is critical to the future of your farming operation or the opportunity to rent or sell the land in the future for a good price.”
Source: NDSU Crop and Pest Report
This article published in the August, 2012 edition of DAKOTA FARMER.