At the Pest Management Field Day recently held at the Arlington Agricultural Research Station, weed science graduate research assistant Tommy Butts presented on one of the greatest threats to Wisconsin agriculture.
Herbicide-resistant weeds, the nemesis of farmers, have been slowly spreading across the country. Glyphosate-resistant common waterhemp has already been confirmed in 15 other states, including Illinois, Indiana, Iowa and Minnesota.
“Wisconsin was bound to be next,” says Butts.
Suspected glyphosate-resistant common waterhemp populations were identified in August 2013 from fields in Eau Claire and Pierce Counties, and suspected glyphosate-resistant Palmer amaranth was identified during the same month in a field in Dane County.
It was the Late Season Weed Escape Survey in Wisconsin Corn and Soybean Fields that caught the intruders, conducted by previous graduate research assistant, Ross Recker.
Graduate research assistant, Butts, introduced himself at the field day as “the pigweed guy” and relayed the bad news, noting that common waterhemp and Palmer amaranth are part of the pigweed family.
Butts’ calm tone turned serious as he detailed the risks associated with these problematic weeds.
“I believe both common waterhemp and Palmer amaranth are equally threatening to Wisconsin’s agricultural community,” he said. “Both pigweed species are prolific seed producers with more than 250,000 seeds produced per female plant. They are highly adaptable, with herbicide resistance to six modes-of-action across the U.S. And they also are extremely competitive with our crops, showing yield reductions greater than 70 percent in corn and soybeans.”
A mode-of-action is the overall manner in which an herbicide affects the plant at the tissue or cellular level. In other words, some pigweed species have evolved to resist six ways that herbicides are intended to kill them.
His alarm was clear. These two weed species need to be managed carefully, and growers were ready to listen.
Scientists at the UW-Madison weed science program are conducting a dose response study on Palmer amaranth as well as common waterhemp. Weed scientists collected seed from mature plants of each species in the field, and they are growing the plants suspected to be resistant in a UW-Madison greenhouse.
To confirm glyphosate resistance, 10 plants per glyphosate rate are sprayed with Roundup PowerMAX plus ammonium sulfate at 17 pounds per 100 gallons of spray solution when they reach 3 inches tall. Plant dry biomass data is collected 28 days after application.
Weed scientists then determine the effective glyphosate dose needed to reduce plant dry biomass by 50 percent two repetitions are needed for official glyphosate resistance confirmation.
Butts and his advisor Vince Davis are key to the investigation, and they recently published the preliminary data of the glyphosate-resistant Wisconsin common waterhemp at http://wcws.cals.wisc.edu/.
At the field day, Butts expressed a mix of alarm and wonder for the pigweed family.
“It’s amazing how they adapt so quickly to a new environment or management practice,” he says. “And how their biological characteristics have set them up to succeed in survival and reproduction; however, it can be quite scary to consider some of the implications these characteristics can pose on our current agricultural practices.”
Butts emphasized to growers that diversifying management practices is a necessity.
“The key for preventing herbicide-resistant weeds is diversifying our weed control practices and using multiple control strategies in an integrated weed management approach,” he says. “It is a necessity to use alternate, effective herbicide modes-of-action.”
Butts suggested that growers use a residual preemergence herbicide application in order to reduce the number of weeds exposed to a postemergence application and hopefully reducing the likelihood that weeds develop resistance.
He also recommends crop rotation and tillage, as well as taking special care to clean tillage and harvest equipment thoroughly as they can quickly spread weed seed among fields.
“We as Wisconsin farmers should take a proactive approach in controlling our weed species as the number of herbicide-resistant weeds continues to rise in surrounding states.” Butts told growers. “It is vital to use best management practices for weed control and implement multiple control methods in an integrated system.”
The Wisconsin weed science program will continue to monitor and investigate potential herbicide resistance issues for weed species across the state.
For more information, visit www.takeactiononweeds.com or contact Davis at 608-262-1392 or Butts at 608-214-4215.