Research Suggests Ducks Spreading Roundup-Resistant Weeds

Dec 6, 2016

A group of mallards dabble in a pond at Forum Nature Area in Columbia.
Credit Sebastián Martinez / KBIA

As the winter moves in, several species of ducks are making their way into and through Missouri, en-route to their overwintering grounds. While this time of year is a boon to duck-hunters, recent research suggests ducks moving through might soon be an ominous sight for farmers.

On an overcast Sunday afternoon, I found a group of mallards – known as a raft – dabbling in a pond at Columbia’s Forum Nature Area. The ducks were foraging for food, alternating between plunging their heads under the water, and being on alert, keeping an eye out for predators, or public radio reporters. Being on city property, the mallards didn’t have to worry about potential hunters. But it was a group of hunters, along with researchers at the University of Missouri, who recently discovered how these ducks’ eating habits could impact agriculture in the state.

Kevin Bradley, a state extension weed scientist and a associate professor in the division of plant sciences at the University of Missouri, is something of a weed expert. So when he heard that a particularly nasty weed was popping up in places it hadn’t before, it got his attention.

"Palmer Amaranth is one of our pigweed species that is probably the number one weed to watch in the United States right now," Bradley said. "It’s a very competitive, fast-growing pigweed species. It can grow about two to three inches per day."

Palmer amaranth is a glyphosate-resistant pigweed species.
Credit Michael J. Plagens / Wikimedia Commons

The weed represents a particular threat to soybeans, one of the Missouri’s biggest crops. Originally only found in the Boot-heel, a few years back Bradley started to see infestations in the state’s northern counties, and there seemed to be a trend.

Bradley explained, "We saw more and more as each year passed, and in each case, it always seemed to be in river-bottoms; either the Mississippi river or the Missouri river bottoms."

And that's where the ducks came in.

"One of the things we began to test is whether waterfowl had any role in the transport or the movement of Palmer Amaranth in the United States," Bradley said.

Bradley and his colleagues hypothesized that ducks and other waterfowl were increasingly consuming Palmer Amaranth and subsequently passing the seeds in their droppings, expanding the plant’s range. To test that hypothesis, Bradley and his team turned to a series of experiments, and duck guts.

"We gathered hunter-donated ducks and geese for two seasons. So we’d dissect those carcasses and look for the seeds and harvest any seeds out of there."

And they found the seeds, sometimes a lot of them, which led them, logically, to confirm whether the seeds the ducks digested were still viable – that is, would they still grow. Answering that meant employing some live ducks.

"We did a live feeding experiment with mallards. We had a controlled amount of seed that we fed these birds and we harvested them every two hours in their feces," Bradley said.

So, after digging through duck guts and then duck poop for seed, Bradley and fellow researcher Jaime Farmer, then a graduate student at the university, found the seed did in fact stay viable.

And that represents a potentially big problem. A lot of crops these days are genetically modified to resist glyphosate – a powerful herbicide that takes care of most weeds. But now some weeds have developed a resistance to glyphosate as well, and Palmer Amaranth is one of them. Coupled with the fact that mallards and other ducks range for thousands of miles across the continent, that makes managing the spread of the weed a tall order.

"We don’t have a major, what do you do," Bradley explained. "But having said that, it’s just basically raising awareness of the potential for Palmer Amaranth to spread."

Back at the pond the ducks, done with their foraging for now, took off all at once. The growing season has passed, and it’s unlikely these mallards have any amaranth seed in their bellies. But come springtime, that could change.