COLUMBUS, Ohio — Many call it “the weed from hell.” Some agronomy experts call it the Rocky of invasive weeds, referring to the movie boxer. Everyone agrees it has made its way into Ohio and it has to be dealt with quickly.

Palmer amaranth, a weed known to many cotton and soybean growers in the South as “pigweed on steroids,” has been spotted in Ohio, prompting Ohio State University extension experts to warn growers to take measures to prevent its further spread.

The plant, which is a glyphosate-resistant weed that has had a substantially negative impact on yields and profitability for cotton and soybean growers in Southern states, has been spotted in a large field near Portsmouth, in extreme southern Ohio. Estimates are the damage from the aggressive weed has reached millions of dollars.

“The concern about Palmer amaranth, which has caused entire cotton and soybean fields to be mowed down in some Southern states, is that if the weed takes hold in Ohio crop fields, it will be even harder to control than the glyphosate-resistant weeds already present statewide,” said Mark Loux, an extension weed specialist.

“Not only is Palmer amaranth resistant to glyphosate, this weed’s rapid growth, large size, extended duration or emergence, prolific seed production and general tolerance to many herbicides makes it a much more formidable weed to deal with than the pigweed species we already have here in Ohio. Among the weeds that we already deal with, Palmer amaranth is going to require pre- and post-emergence applications, possibly multiple post-emergence applications.

This invasive weed can grow three inches in a single day and can release nearly a half-million seeds per plant. Many growers in the Southern states have already had to hire workers to enter the fields and chop down the weeds with hoes and pull them by hand. In some cases the fields had to be plowed over, killing existing crops as well as the weeds.

“It’s already resistant to two of the main types of herbicides we use in soybeans, glyphosate and ALS inhibitors,” Loux added, “and the weed has to be less than four inches tall when spraying in order to get control of it.”

Palmer amaranth has been spotted in Michigan and Indiana, as well.

“We suspect Palmer amaranth was introduced in Ohio and other states through contaminated cottonseed shipped from the southern U.S. for use as animal feed here in the Midwest,” Loux said. “Palmer amaranth established from manure spread on fields that was obtained from these animal operations.”

Loux suggests growers and producers stop spreading manure obtained from animal operations where cottonseed was used as feed. The ultimate goal is to prevent the spread of this weed. Ohio growers have enough to contend with, he pointed out, considering things like marestail, giant ragweed, common ragweed and waterhemp are found throughout the state.

Drought conditions only abet the growth of the weed. Extended heat and drought impact the germination, hardiness, growth and competitive ability of weeds and complicate control efforts.

During dry conditions that Ohio and neighboring states have undergone this year, weeds grow more slowly and also develop thicker cuticles on the leaf surfaces, and that reduces herbicide movement through the plant.

“This weed is difficult to manage and can become very expensive,” Loux said. “We have enough information to hopefully prevent additional infestations of an extremely aggressive weed. There could be long-term consequences for farm profitability for failing to do so.”