Wisconsin farmers and land managers planting conservation seed mixes this spring should keep an eye out for an aggressively invasive weed called Palmer amaranth. State plant protection officials at the Department of Agriculture, Trade and Consumer Protection caution anyone packing and labeling such seeds to take steps to avoid contaminating the mixes with Palmer amaranth.
Under a new emergency rule in Wisconsin, Palmer amaranth is a prohibited noxious weed seed, and including it in a seed mix would be a civil or criminal violation for the seed labeler.
“Once established, Palmer amaranth can outcompete other native plants in conservation plantings, and if it gets into corn and soybeans, can cause yield losses as high as 90%,” says Brian Kuhn, director of the Plant Industry Bureau at DATCP. “This is an incredibly invasive, incredibly expensive-to-control weed. It’s been highly destructive in some of our neighboring states, and we don’t want to see that in Wisconsin.”
What is Palmer amaranth?
Palmer amaranth is a broadleaf weed that, well, grows like a weed — up to 2 to 3 inches per day. It commonly grows 6 to 8 feet tall but may reach 10 feet. It has separate male and female plants, and the females may produce as many as 500,000 seeds. It is related to waterhemp and other pigweeds common in Wisconsin, and a casual observer might confuse the two.
Native to the southwestern United States, Palmer amaranth has now spread to nearly all of the southern half of the country and several Midwest states, including Indiana, Illinois, Iowa and Nebraska. In the past, the weed seed usually was spread on equipment, in feed or by wildlife, so it didn’t spread very rapidly and could be eradicated in a field fairly easily. It has been found in a handful of sites in Wisconsin where it was brought in by these methods, according to DATCP officials.
But in recent years, Palmer amaranth has gotten into seed mixes that farmers plant as pollinator habitat on conservation acreage, such as land in the Conservation Reserve Program. Left to go to seed in these areas, it spread to new areas rapidly. Iowa has had a particularly severe problem, with more than half the counties there now infected with Palmer amaranth. To date, Wisconsin has not found Palmer amaranth in conservation plantings.
“We want to keep it out of Wisconsin as long as possible,” Kuhn says. “Our pest surveyors have been trained in spotting Palmer amaranth, with help from the University of Wisconsin-Madison. We’ve sent information to our licensed seed labelers. And now we need landowners to join the effort.”
Anyone planting a pollinator or conservation seed mix should:
• Be aware of what Palmer amaranth looks like. (See photo above).
• Buy local seed mixes if possible, with no pigweed or amaranth listed on the label.
• Thoroughly clean equipment after seeding, especially if your seed mix came from out of state.
The weed is highly mobile and can be glyphosate-resistant. The glyphosate-resistance trait can be moved by pollen. How far will that pollen travel? Research in Georgia has shown pollen from resistant males can fertilize susceptible females at least 1,000 feet away. So, the resistance trait can easily be spread from field to field by pollen.
Call your county Extension office if you suspect you have found Palmer amaranth.