Superweeds crowding in on corn, beans in Midwest
ROCKFORD - Farmers may soon have more trouble controlling weeds in northern Illinois.
A dozen weed species have evolved to resist glyphosate, the active ingredient in the country's most widely used farm and garden herbicides. The herbicide, when paired with Roundup Ready corn and soybeans hybrids that are also resistant to glyphosate, gave farmers a potent tool to kill weeds and not their crops for two decades.
But now the weeds are imitating the crops. The herbicide won't kill them. And now they're on the move, extending their range from south to north.
Two of the most worrisome species on the move in Illinois are cousins from the pigweed family - Palmer amaranth, a species indigenous to the desert Southwest, and common waterhemp.
"It certainly has been a hot topic this winter," said Russ Higgins, a University of Illinois Extension crop scientist at the Northern Illinois Agronomy Research Center in Shabbona. "The big news in 2014 is going to be Palmer and trying to control it."
Pigweeds are prolific species. A single plant can produce up to 1 million seeds. They can grow up to 2 inches a day and reach 7 feet. Infested fields can bring costly trouble for farmers, who must use other herbicides or physically remove the plants.
Higgins said a resistant-strain Palmer amaranth has been documented Grundy County but hasn't been found in Winnebago, Boone, Ogle or Stephenson counties. Last fall, however, it was discovered in a field in Dane County, Wis., raising concern among scientists.
"Palmer amaranth competition with crops has demonstrated yield losses as high as 78 percent (for soybeans) and 91 percent (for corn)," according to Wisconsin Crop Weed Science at the University of Wisconsin.
Could it already be in northern Illinois?
"It quite likely is," Higgins said, and the key for farmers is to deal with the plant before it has a chance to infest a field over a couple of years.
Waterhemp is another field pest that is causing a stir among farmers in the region. Higgins said that last year the University of Illinois offered to test waterhemp in the area for glyphosate-resistance traits. The lab expected 400 samples; it got more than 1,000.
Aaron Hager, a University of Illinois weed scientist who was warning in 2005 that herbicide-resistant strains of pigweed were likely to move into Illinois, said genetic abnormalities in plants allow them to evolve and survive in new conditions. It's called natural selection.
The mutation may occur in 1 in 1 million or 1 in 1 billion plants. But if one or two abnormal plants survive, they can produce seeds that create more plants with the resistant gene. They take over fields.
"There are very few good things that weeds to do crops," said Hager, who spoke at a recent crop management conference at Kishwaukee College in Malta.
"They're plants just like the corn is or soybean is and they have many of the same resource needs the crop does."
Hager urges farmers to be vigilant in their fields this year so they can stay ahead of the invaders. He said a farmer in Arkansas reacted too slowly to a glysophate-resistant pigweed infestation. Five years later, the farmer was out of business.
It's serious, he said.
"Over time, resistant ones outnumber susceptible ones, and you see a shift in your populations."
Brian Leaf: 815-987-1343; bleaf@rrstar.com; @b_leaf
