Ohio State offering free weed herbicide resistance screening

Redroot pigweed is everywhere and generally easy to control, but some fields are developing pockets of resistance. It’s one of the weeds Ohio State wants to help farmers ID and plan to manage. (Steve Dewey/Utah State University photo)

COLUMBUS — As growers prepare for the coming winter, understanding herbicide resistance can help them combat the weeds in their fields in the most cost-effective and efficient way.

Members of the Ohio State University Weed Team are providing growers with free screenings of populations of any pigweed species this fall. The screenings can help farmers know what to expect from an herbicide as they try to manage weed infestations in their fields, said Mark Loux, an Ohio State University Extension weed specialist.

Knowledge is power

“The screenings can help farmers make their most effective herbicide choices,” he said. “Growers should avoid using the wrong herbicide on the weeds that are already resistant to certain herbicide sites of action, or in some cases adding in another postemergence herbicide before they actually have to.”

Not only will that make the weeds more difficult to control, Loux said, but growers can end up wasting money in the process.

Related story: You do NOT want to find this weed in your fields

Weed ID

The weeds that can be screened include populations of redroot pigweed, waterhemp and Palmer amaranth, among others, Loux said. Samples should generally be collected from fields where resistance to one or more types of herbicide is suspected, he said.

“Redroot pigweed is everywhere and generally easy to control, but some fields are developing pockets of resistance,” Loux said. “Fields with waterhemp are increasing slowly across the state, and most fields have one or more types of resistance. However the biggest weed concern is trying to keep Palmer amaranth from getting firmly established in Ohio because it is very difficult to control.”

Submit yours

Growers can submit weed samples to members of the Ohio State weed team for free for analysis. The sample submission form with directions for collecting seed can be found at the Herbicide Resistance Screening link at u.osu.edu/osuweeds/.

Guidelines for collections are as follows:

  • Samples should be collected when seed is mature. Fully developed seed will be hard, not soft.
  • Collect entire seedheads.
  • Depending on the species, 10 to 30 seedheads will be needed to have enough seed for a proper screening.
  • Samples should be fresh. Mail immediately or let air dry under cool, dry conditions in an open paper bag for two to four weeks. Do not collect or store in plastic.
  • Samples should be carefully packaged and shipped early in the week to avoid weekend layovers during which the sample will deteriorate.
  • Be sure to include sample documentation and background information.


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