Now is the time to be checking fields for Palmer amaranth and making sure it doesn’t go to seed, according to Tom Peters, North Dakota State University Extension sugar beet agronomist.

Often referred to as the No. 1 weed problem in the U.S., Palmer amaranth — a type of pigweed that has devasted crops in the South and parts of the Midwest — has been identified in South Dakota, Minnesota and Iowa but hasn’t been found in North Dakota yet.

The key to keep it from becoming a problem is identifying it and preventing it from developing and spreading seed, Peters says.

Palmer amaranth is aggressive and competitive, growing 2 to 3 inches per day in optimum conditions. The plants can grow to be 6 to 8 feet tall, and a single plant can produce up to 1 million seeds. Palmer amaranth also is hard to control because it is very prone to being resistant to herbicides.

SEED HEADS: A Palmer amaranth plant begins to develop seed heads. The seed heads can grow up to 2 feet long.

Unlike other summer annual weeds that need to be controlled only through early summer, Palmer amaranth emerges throughout the growing season, says Brian Jenks, weed scientist at NDSU’s North Central Research Extension Center, Minot.

Scouting tips
The first step in managing Palmer amaranth is to look for it and identify it.

"Scout areas for plants that don’t look right," Peters advises.

Now is a good time to scout because Palmer amaranth is developing its distinctive long, snaky seed heads, he says. The seed heads can grow up to 2 feet long.

Identifying Palmer amaranth can be difficult because it resembles redroot pigweed, smooth pigweed and waterhemp.

Here are some ways to distinguish Palmer amaranth from similar-looking weeds:

• Seedlings have egg-shaped leaves and may have a hair-like protrusion on the leaf tip.

• The leaves and stem have few or no hairs.

• The petiole (leaf stem) will be as long as or longer than the leaf blade.

TALL PLANT: Palmer amaranth can grow to be 6 to 8 feet tall.

Visit NDSU Extension’s Palmer amaranth website at ag.ndsu.edu/palmeramaranth to learn more about the weed and how to identify it.

How it spreads
Palmer amaranth seeds can spread in several ways, including by farm equipment, wildlife, wind and water. Seeds also have been found in native seed mixes used for pollinator or wildlife habitats and in hay. Because donated hay came into North Dakota in 2017 during the drought, producers need to be on the lookout for Palmer amaranth and other weeds along highways and roads, and where cattle were fed.

People who see a plant they suspect is Palmer amaranth should contact their local Extension agent or an Extension specialist as soon as possible.

"This weed is a game changer and will be controlled only by a zero-tolerance policy," Jenks says.

Source: NDSU Extension