Palmer amaranth with multiple herbicide resistance is nothing new to the Mid-South. But farther north, the recent discovery of pigweed resistant to glyphosate and PPO herbicides was novel.
Where and how was the pigweed found?
“We’re reporting this because it’s in our state,” says Kevin Bradley, University of Missouri weed scientist. “However, it really was discovered as a result of a retailer sending suspicious pigweed samples, Palmer amaranth in a soybean field, in for testing.
“The University of Illinois has a service they provide – a rapid screening of different types of herbicide resistance. They can turn a sample around in a day, or two.”
Outside the Bootheel, “we don’t really have a lot of Palmer in Missouri,” says Bradley, who was reached by phone in an airport before heading out of the country for several weeks. “There is a pocket around St. Louis in the river bottoms. That’s where these pigweeds were found. Once tested, the sample came back positive for resistance to glyphosate and PPO herbicides.”
Bradley and colleagues “wanted to let people know about this find” so they can be on the lookout. “The Midwest has been dealing with multiple-resistance waterhemp for over 10 years. Considering everything, I wouldn’t characterize this Palmer find as a big shocker.
“As far as I’m aware, so far, this is the farthest north multiple-resistance pigweed has been found. There’s glyphosate-resistant Palmer amaranth all the way into Michigan and Indiana. But I’m unaware of any of that has PPO resistance.”
What about university recommendations for control?
“As far as management our recommendations for control aren’t any different than those for multiple-resistance waterhemp.