Palmer amaranth, which is a glyphosate-resistant weed that has had a substantially negative impact on crop yields and profitability for cotton and soybean growers in Southern states, has been spotted in a large field near Portsmouth in extreme southern Ohio, says Mark Loux, an OSU Extension weed specialist.
The concern about glyphosate-resistant 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, he says.
"Not only is Palmer amaranth resistant to glyphosate, this weed's rapid growth, large size, extended duration of 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," Loux says. "Among the weeds that we already deal with, Palmer amaranth is going to require pre- and post-emergence applications, possibly multiple post-emergence applications.
"It's already resistant to two of the main types of herbicides we use in soybeans, glyphosate and ALS inhibitors, and the weed has to be less than four inches tall when spraying in order to get control of it."
Palmer amaranth, which can grow 3 inches a day, can release nearly a half-million seeds per plant. And because the weed is glyphosate-resistant, many growers in Southern states, in addition to spraying, have had to hire workers to go into their fields to chop down the weeds with hoes and pull them by hand.
Losses for growers dealing with this aggressive weed have been in the millions in lost agricultural crops, experts estimate.
The weed, which has typically been prevalent in Southern states, is moving north, with several other suspected cases statewide that OSU Extension experts are investigating. New infestations of Palmer amaranth have also been found farther north, in Michigan and Indiana, he says.