• By Vicky Boyd,
BASF recently launched an industrywide initiative – “Operation Weed Eradication” – that challenges growers and others within agriculture to take a zero-tolerance approach to ridding fields of devastating weeds.
“As an industry, we’ve talked about managing weeds. We need to switch that up to eradicating those weeds in the field,” Scott Kay, vice president of U.S. Crop Agricultural Solutions North America, told attendees of a recent BASF media event.
The call to arms was prompted in part by research by Stratus Ag that showed nearly 75% of growers nationwide are dealing with glyphosate-resistant weeds in their fields, he said. And today’s management practices are not sustainable for long-term control of problem weeds, such as pigweed.
More than two-thirds of soybean producers also have changed their systems during the past three years because current weed-management practices weren’t sustainable, Kay said.
Herbicide-resistant Palmer amaranth, also known as Palmer pigweed, plagues about 29% of farmers nationwide and infests 45 million acres, he said.
A 2017 Weed Science Society of America survey of its members ranked Palmer amaranth as the most troublesome and difficult to control weed in 12 categories of broadleaf crops, fruits and vegetables.
One reason for the top ranking is a single female plant can produce upward of 600,000 seeds. Under optimum conditions, a Palmer pigweed plant also can grow up to 2 inches per day, outcompeting commercial crops for nutrients and moisture.
With thin margins and growers spending 3.5 times more on weed control today than they did just 10 years ago, BASF has elevated the goal of a weed-free field at harvest, Kay said
A community effort
To be successful, Kay said, growers will need to work together since weeds don’t respect property boundaries. If one grower has a weedy field, the seeds can be moved by wind, equipment, birds or other means and jeopardize an area-wide program.
The effort also cannot be one size fits all but rather a personalized approach for each farmer. In addition, it needs to include several different measures, including rotating effective modes of action, cultivation, different cultural practices, crop rotation, hand roguing and attention to detail.
“We need to look at that last weed standing as the strongest weed in the field,” Kay said.
Back to the future
The concept of zero tolerance toward weeds with high productive rates, such as Palmer amaranth, is nothing new.
Earlier this decade, University of Arkansas Cooperative Extension conducted grower education on the importance of zero tolerance for glyphosate-resistant Palmer amaranth, said Dr. Bob Scott, who at the time was Extension weed specialist. He is now director of the university’s Rice Research and Extension in Stuttgart.
“The concept of zero tolerance is alive and well, whether people call it that or not,” he said, adding that zero tolerance is different from eradication.
The University of Arkansas’ education focused on prevention. Even a single resistant pigweed plant that went through a combine could forever infest a field, Scott said, citing research by colleague Dr. Jason Norsworthy. Instead, Extension specialists urged growers to pull the few pigweeds in their field to prevent a much larger problem from developing.
“It really could make a difference – a big difference – long term,” Scott said.
And he said he believed the zero-tolerance message got through to a lot of growers.
When Scott first became director of the rice research facility in 2018, a neighboring grower called him out about pigweed along the station’s south border.
“Around here, they don’t let those things to go seed,” the grower told Scott, who promptly grabbed a hoe and removed the 14 offending pigweed plants.
A growing list
The problem of herbicide-resistant Palmer pigweed has continued to expand, both in acreage as well as the number of chemicals to which the weed has grown resistant.
Earlier this year, Kansas State University researchers confirmed a Palmer amaranth biotype resistant to Group 4 herbicides, including dicamba and 2,4-D.
University of Tennessee Extension weed specialist Larry Steckel is following up on similar grower reports that the latest generation of dicamba products is not controlling pigweed like they did when the Xtend system was first introduced in 2013. He plans to conduct laboratory trials this winter to confirm his hunch about dicamba resistance.
Steckel wrote about his concerns this summer on a university blog, prompting a grower to ask Scott about the potential for custom harvesters to spread resistant Palmer pigweed seed.
Scott said it is a valid concern, adding equipment sanitation between fields is going to take on more importance.
In addition, Dr. Jason Norsworthy and Tom Barber, both University of Arkansas weed scientists, have confirmed Palmer pigweed populations in Northeast Arkansas with multiple resistance to S-metolachlor, a Group 15 herbicide, and glyphosate.
These latest findings join the growing list of herbicides to which Palmer amaranth has become resistant. They are Group 2 (ALS inhibitors), Group 3 (dinitroaniline such as Treflan), Group 5 (atrazine), Group 9 (glyphosate), Group 14 (PPOs) and Group 27 (HPPD inhibitors).
Although several Palmer amaranth populations resistant to two different modes of action have been confirmed, researchers in Kansas and Arkansas have found populations resistant to five different modes of action.
For more information on zero tolerance, including management tips, download University of Arkansas’ “Zero Tolerance: A Community-Based Program for Glyphosate-Resistant Palmer Amaranth Management.”