Corn Belt Preps For Fight With Palmer Amaranth

Des Moines Register:

Hartzler, Owen and others are trying to determine whether Palmer amaranth, discovered in Iowa last year, is resistant to glyphosate.
"If I was a betting man, and I am, I'd say we've got glyphosate-resistant Palmer in Iowa," Owen said. Hartzler believes the superweed is likely growing in more than five counties.
The tiny seed spreads easily — by farm equipment that moves across state lines and fields, in cotton byproducts that are fed to dairy cows, even potentially by birds, experts say.
The states around Iowa are already fighting glyphosate-resistant Palmer amaranth, including Illinois, Missouri and Kansas.
Waterhemp, a similar-looking but wimpier cousin of Palmer amaranth, is resistant to glyphosate and other herbicides in Iowa. "At least 50 percent of fields in Iowa have waterhemp that's resistant to glyphosate. It's our No. 1 weed problem," Hartzler said.
It's difficult to distinguish between waterhemp and Palmer amaranth, both pigweeds, especially when they're small, he said. But Palmer amaranth is stronger and faster-growing. It can quickly overrun a soybean crop. Corn is tougher in a matchup.
Waiting even a long weekend to kill Palmer amaranth can result in the plant getting too large to kill with a herbicide. The weed can grow 2 inches a day and needs to be sprayed when it's 4 to 6 inches in size.
Add spring rains or wind to the equation, and farmers can quickly miss the window, Hartzler said.
Already, U.S. farmers are being forced to use more herbicides to control waterhemp. "We've already seen a big leap, and Palmer amaranth will increase it more," he said.
A Muscatine County farmer who discovered Palmer amaranth last fall decided to mow down part of a soybean field to control it. "He knew if he tried to harvest it, the Palmer amaranth seed would get inside the combine, and it's nearly impossible to clean it out," said Hartzler, who determined that weed wasn't yet resistant to glyphosate. "He didn't want to spread it to other fields."
The Iowa Soybean Association has asked farmers to carefully scout fields and nearby ditches for Palmer amaranth. They're being urged to treat any pigweed like it's herbicide-resistant, meaning aggressively stamping it out when it's small.
Young, the Arkansas farmer, said he initially thought he had missed spraying a small patch of weeds that turned out to be resistant to Palmer amaranth. Within a short time, the weed had spread to all the fields he farms.

On the optimistic side, Palmer Amaranth in the corn belt may prove to be an over-hyped threat like soybean rust turned out to be.  We spent around 2 or 3 years in the mid 2000s freaking out about soybean rust, and the the damage hasn't materialized. Yet (climate change may make it a longer-term threat).  On the more realistic side, it is obvious that Roundup-resistant weeds are going to be a long-term problem, and I know of no reason why Palmer Amaranth can't spread from Arkansas to the corn belt.  Maybe the shorter growing season and the harsher winters will help us in checking its spread.  Maybe the time spent fighting it down south will give the chemical companies a chance to develop new products to use in the fight.  I'm not extremely worried about it yet, but it is defintely something to keep an eye on.