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Not All Palmer Amaranth Plants Look the Same

TAGS: Crops
Not All Palmer Amaranth Plants Look the Same
Educator says it doesn't really matter; if it's an offshoot assume you need to control Palmer amaranth.

Let's hope you're fortunate enough not find Palmer amaranth in any of your fields. It's been positively identified in about one-fourth of Indiana counties. Most recently it was positively identified in Shelby County in south-central Indiana.

How did it get there? It's conjecture, but this field isn't on a livestock farm or near a big diary. No manure has been spread. But it does lie along a river. One theory is that the seed moved down stream, but no one knows from where or exactly how the process might work.

Scott Gabbard, Shelby County Extension ag educator, says that if you have river bottom fields in particular, it would pay to be looking for it.

Maybe, maybe not! This Palmer amaranth plant has a hair on the tip of leaves. However, not all Palmer amaranth plants do, scientists say. It's not a positive identification point.

Related: Palmer Amaranth Can Be Hard to Spot in Tall Beans

"If you find something that looks like it, bend back the petiole. If it is longer than the leaf and the plant looks like a pigweed, it's worth following up on. Take it to an extension office. The educator will likely want Bill Johnson, Purdue University weed specialist, or one of the other [Soil and Water Conservation Districts] scientists on staff to make a positive identification.

"What we're finding is that some don't look exactly like others," Gabbard says.

The plant has male and female versions. Since it has open pollination, he believes that is why some plants in the same population can look different.

Some look for a watermark or hair on the tip of the leaf. While either one or both may be there, neither may be there and it is still Palmer amaranth. To complicate matters further, some tall waterhemp plants have been found with watermarks. That's why these watermarks, or chevrons, aren't positive identification for Palmer amaranth. However, they do signify that if the year present and the plant resembles a pigweed, it's worth identifying what species it is.

Related: A Week Can Make a Huge Difference in Palmer Amaranth Growth

Regardless of exactly what the plants look like, treatment will likely be the same. Get any you can out of your field now, roots and all, and plan on using a herbicide program designed for glyphosate and ALS resistant Palmer amaranth next season.


In the coffee shop, it is known as Palmer pigweed. In university circles, it is referred to as Palmer amaranth. Whatever you want to call it, this weed is the No. 1 weed to watch. Stay on top of your control plan with our new free report, Palmer Amaranth: Understanding the Profit Siphon in your Field.


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