WEST LAFAYETTE, Ind. — A weed normally found in Southern cotton fields has taken root in more than 50 fields in five northwestern Indiana counties.

Travis Legleiter, a weed science program specialist at Purdue University, said that may be just the tip of the iceberg.

Palmer amaranth, a relative of pigweed and waterhemp, has apparently been growing for at least two seasons in Indiana and has been misidentified as waterhemp.

“They’re all related; they’re all varieties of amaranth,” said Legleiter. “Our suspicion from looking at those fields is that it’s been there for the past two or three seasons.”

There are 42 affected fields in Jasper County, five in Newton County, two in Pulaski County and one each in LaPorte and Cass counties. According to a Purdue Weed Science Bulletin issued in October, Palmer amaranth is the most competitive of the amaranth species and can result in a devastating economic impact on crops.

It is glyphosate-resistant and in the South, entire cotton fields have been abandoned because of an inability to control it. The plants growth up to seven feet tall and on hot summer days can grow 2-3 inches. One female plant is capable of producing more than half a million seeds.

Legleiter said the key to combating the plant is proper identification. This is difficult because Palmer looks almost identical to pigweed, and the steps to control pigweed won’t work on Palmer.

Looking at Palmer amaranth from above, it will appear to have a rosette shape with ovate leaves and long petioles (the stalk that joins the leaf and stem) similar to a poinsettia. It is hairless and will have multiple seed heads, but will be distinguished with one main seed head that can reach 2-4 feet in length. The main seed head will be spiny.

How Palmer amaranth made it to northwestern Indiana is anyone’s guess, but Legleiter said it’s certain it was brought here by humans. The best guess is that it arrived in manure from cattle that were fed cottonseed from the South.

But now that it’s here, Legleiter said it’s important for farmers to know about it and what to do. “The first thing is to identify it. We have to know what weeds we’re spraying for,” he said.

If Palmer is present, Legleiter said the first step is to rotate crops and herbicides. Most farmers use a post-emergent herbicide and that isn’t effective on Palmer. Legleiter said farmers should use pre-emergent herbicides on both corn and soybeans.

Some post-emergent herbicides can help with infestations in corn, but those with soybeans must start with a clean field that has been fully tilled and then covered completely with a pre-emergent residual herbicide.

“If it does end up getting into your crops, there’s not a lot you can do about it,” said Legleiter. “You could lose control of your field in a single year if you’re not vigilant.”

He and others at Purdue who have examined the affected fields in Indiana feel it has been here for awhile. “We’re kind of behind the curve on this one, but we’re working hard to get caught up,” he said.

Legleiter said Purdue will be sponsoring a series of workshops around the state after the first of the year to talk about Palmer amaranth and what farmers can do about it.

This isn’t the first discovery of Palmer in the state, but it is the first in upland fields in northern Indiana. Last year, Palmer amaranth was discovered in river bottom fields in Posey and Vanderburgh counties along the Ohio River in southwestern Indiana.

A Purdue Weed Science Bulletin said there are several corn pre-emergent herbicides that include atrazine premixes, which will reduce the number of plants that emerge and require post-emergent application. In addition, there are a number of post-emergent corn herbicides that will control Palmer, including HPPD inhibitors and growth regulators.

In fields heavily infested with Palmer amaranth, farmers should grow corn for several years because the number of effective herbicides and mode of action rotation is more effective than with soybean applications.

Anyone who suspects their fields contain Palmer amaranth should contact their county extension agent.