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How to Identify Palmer Amaranth

Jeff Gunsolus, Extension weed scientist at the University of Minnesota, walks around with a weed in a bucket at university field days. The culprit is Palmer amaranth, and it stays in the bucket. He doesn’t want the native desert Southwest weed to become his legacy. “We don’t need anymore weed problems: We have enough of our own,” says Gunsolus.

The drought-tolerant weed shares characteristics with waterhemp. However, it grows faster – at 2 inches per day – and is more competitive, warns Gunsolus. While it’s been perceived as a Southern weed, it’s on the move. There have been reports of Palmer amaranth from Indiana to Wisconsin and even southern Iowa. He expects that it spreads through livestock manure, CRP, and other plant material.

When scouting, trying to differentiate Palmer amaranth from waterhemp can be a challenge, but here are a few tips from Gunsolus.

Check the details

Palmer amaranth has a long petiole, and the leaf is more ovate or round, says Gunsolus. Waterhemp has a short petiole and a longer, narrow leaf. At the end of a Palmer amaranth leaf is a tiny notch with a little spike. Palmer amaranth also looks waxier, and it can have a little thumbprint where the leaves unfurl, says Gunsolus. Another key to look for is the spiky seed head – one plant can produce 1 million seeds.

If spotted
“You could report it to somebody, but don’t leave it in the field,” says Gunsolus. “Bag it so if there is any seed, it doesn’t spread. Pull it out of the field, and burn it.”

If you treat it aggressively, as you would waterhemp, you should be able to manage it, says Gunsolus.

“You would manage it just like you would manage waterhemp, which would be very aggressively with soil preemergence herbicides and effective postemergence herbicides,” says Gunsolus. “What we are concerned about is that a lot of Palmer amaranth is already becoming resistant to a couple of classes of chemistry – often to Roundup, the site of action 9. Often to the site of action 2, the chemistry like Pursuit.  So you’ll start to lose tools right from the get-go. That makes it even more challenging." 

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