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Palmer amaranth test may help in limiting spread
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Palmer amaranth test may help in limiting spread

Palmer amaranth

With herbicide resistance becoming an issue, genetic tests for Palmer amaranth in seed mixes could prevent the weed from entering fields in the first place.

Palmer amaranth has become an annual pest in fields across the Midwest and has been quickly spreading north in recent years. The impact of the weed sparked researchers at the University of Minnesota to find methods to prevent additional spread.

Anthony Brusa, a post-doctoral associate at the University of Minnesota, led a team of 12 in developing a new genetic test for Palmer amaranth, which helps detect the weed in seed mixes being sold to farmers. By scanning these mixes, it can prevent the sale of contaminated seed and therefore limit the exposure of the tough weed.

“We already knew Palmer was a threat in the Southeastern U.S. with quite a bit of impact,” Brusa said. “We knew it was up in the Midwest, and in 2016 it showed up in Minnesota. We knew it wasn’t enough to just identify a leaf from a plant in the field.”

The genetic test developed by Brusa and his team is 99.9% accurate, according to the University of Minnesota, with only one-to-three errors in 1,250 samples.

While herbicides are a good option for those already dealing with Palmer amaranth in their field, Brusa noted the weed’s herbicide tolerance. Using these genetic tests can prevent the seed from ever entering some fields.

“There’s a lot of resistance found in Palmer, including glyphosate,” Brusa said. “Roundup is one of the most commonly used herbicides and there’s a pretty good amount of the population that’s resistant to it.”

It’s not just in seed mixes that Palmer amaranth can spread, however, as North Dakota State Extension specialists pointed out in an article from last fall.

Cattle feed can sometimes contain trace elements of the seed, leading to possible spread in fields in the form of manure. It’s also possible for machinery being used in multiple locations to be contaminated with the seed.

The article suggested keeping equipment clean to ensure Palmer amaranth stays off the farm, as well as doing screenings of grain to help detect the issue before it happens.

“The best way to control Palmer amaranth is not having it enter your farm,” they said.

With this genetic testing available now, Bursa’s goal is to see the test be used commercially and prevent issues with other countries. He said using this test on exports could prevent sending an invasive weed in a soybean shipment to China.

This kind of testing may not be limited to Palmer amaranth, Brusa said. While there will need to be development, he said genetic testing may be helpful when it comes to other common weeds in Midwest fields.

“You could apply the same principle and same type of development that we used in order to target some other weed species,” Bursa said. “Cocklebur, ragweed and Johnson grass — there have been a number of complaints filed against U.S. producers based on those, so being able to identify those is something we are considering looking at.”

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