MINNEAPOLIS (AP) - It’s a beast of a weed, creeping north into the Midwest
from cotton country.
Palmer amaranth can shoot up as high as 7 feet, and just one plant can
produce up to a million seeds. Herbicide is increasingly futile against it,
and the weed’s thick stems and deep roots make it hard work to clear by
hand. It can slash yields and profits when it gets out of control.
Midwestern weed scientists are sounding the alarm because the plant recently
turned up in Iowa and can cause deep losses in corn and soybean yields.
“This is not just a nuisance. This is a game-changer,” warned Purdue
University weed scientist Bill Johnson, whose state has well-established
pockets of the plant.
Cotton growers in the South already spend about $100 million a year to try
to keep it out of their fields, University of Georgia scientist Stanley
“This is a crop robber,” said W.C. Grimes, who farms 1,600 acres of cotton,
peanuts and corn near Twin City in eastern Georgia. “It will steal your
profit. It will choke your cotton out, and anything else you’re trying to
Grimes said he was losing up to 200 pounds of cotton per acre until farmers
learned the key to overcoming Palmer amaranth’s resistance to glyphosate -
sold under brand names like Roundup - was to continuously change herbicides.
His advice to Midwesterner farmers: Keep your eyes open and do whatever it
takes to kill the weed as soon as it turns up.
One thing that makes Palmer amaranth so much tougher than other weeds is
that one plant can produce 500,000 to 1 million seeds. A combine can scatter
seeds from a couple plants across an entire field, Johnson said, and the
untrained eye can’t tell the difference between Palmer amaranth and more
common but less aggressive Corn Belt weeds, such as waterhemp and other
kinds of pigweed.
Palmer amaranth probably took root in Kendell Culp’s fields near Rensselaer
in northwestern Indiana last year, but he wasn’t aware of it until a seed
salesman spotted it this summer. Culp pulled it up by hand - filling a
pickup truck bed from one spot and a half load from another.
“Unfortunately I think it’s going to be a pretty difficult weed to control
for us,” Culp said. He’s working with a consultant on strategies for
deploying herbicides on his 1,750 acres of corn, soybean and wheat.
Palmer amaranth often hitches a ride on dirt stuck to farm machinery. It may
also hide in grass seeds planted as cover for conservation programs, experts
say. But they disagree on whether the seeds spread through animal feed
containing cottonseeds or hulls, which are commonly added to dairy cattle
Johnson said the weed is often seen near dairy farms, and the presumption is
that when manure from those cattle is spread on fields, the seeds can spread
with it. But Culpepper said the research he’s seen doesn’t back up that
theory, adding that spreading the idea without proof could hurt demand for
The infestation found this August in two western Iowa soybean fields
probably got there by truck, Iowa State University weed scientist Bob
Despite those fields being adjacent to a stretch of flood plain with poor
soil where sludge from a Nebraska company has been spread as fertilizer, he
said there’s no reason to think the sludge contained Palmer amaranth seeds.
His suspicion is that the seeds were stuck in mud on trucks that hauled the
But Hartzler’s not convinced the weed will be as difficult to manage as many
fear. Farmers who already take a proactive approach to common waterhemp
should be able to control Palmer amaranth, as long as they try new
strategies, he said.
Given the weed’s resistance to glyphosate, which is typically applied after
weeds sprout, farmers need pre-emergent herbicides to kill the weed earlier
in its growing cycle. Those have a much narrower window of time when they
can be applied.
Palmer amaranth likes long growing seasons and hot, sunny weather, Culpepper
said, so it may not be quite as aggressive in colder states. However, he
said it’s still going to be “the baddest boy on the block.”
The weed isn’t known to have a beachhead as far north as Minnesota, but
University of Minnesota Extension researchers have already advised their
farmers to be vigilant.
“I’d like to say we’re not going to have the problem, but we’re not going to
say that,” weed scientist Jeff Gunsolus said.