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Scouting For Palmer Amaranth

Palmer amaranth can take over a crop field faster than any other annual weed and it’s no picnic to deal with. The trick is to stop it before it gets started by removing the plants before they have the chance to set seed. Be out scouting your fields from now through harvest.

Mark Loux is an Extension weed management specialist at the Ohio State University. He says it’s assumed that most Palmer amaranth is glyphosate-resistant. If you have a Roundup-ready bean program with glyphosate as your POST, it’s typically going to miss it.

"So, what we advocate is some extra scouting late season, certainly some extra trips around your soybean fields with binoculars if you need them, or drone or whatever, to see if there’s something sticking up that you don’t recognize," says Loux. "For us, marestail and giant ragweed are our two late season offenders, so, if it doesn’t look like a marestail or giant ragweed then what is it?"

Loux says a dead giveaway for Palmer amaranth in late summer is the long seed head which is extremely rough to the touch.

Most of the scouting focus is on bean fields because corn will often hide weed infestations. The best scouting time in the corn field is at harvest.

"If you’re harvesting and you come across a patch of something that doesn’t look like a normal pigweed, don’t blow it through your combine," he warns. "Stop, get it identified, figure out what you can do with that before you just kind of plow right through and contaminate the combine and spread it."

Plants without mature seed should be cut off just below the soil surface and burned or composted. Plants with mature seed should be cut off, bagged, and removed from the field to prevent the seeds from dispersing.

Find more tips on scouting for Palmer amaranth

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