Palmer amaranth is in South Dakota. It was found recently in a sunflower field near the Missouri River in Buffalo County, which is in the central part of the state. Gann Valley is the county seat. It's about 85 miles southeast of Pierre.
The SDSU weed science team confirmed that it is Palmer amaranth – a prolific weed that, in other states, is resistant to several herbicides, with glysophate and .
"Palmer amaranth is a vigorous weed that is a member of the pigweed family that also includes common waterhemp, redroot pigweed, prostrate pigweed and others," says Paul O. Johnson, SDSU Extension weed science coordinator.
Native to the southwestern U.S., Palmer amaranth is an annual and only reproduces by seed. However, it is not known the growing season is long enough in South Dakota for it to produce viable seed. The seed might not be able to survive the winter, either, although plants have gotten established in Pennsylvania, Iowa and Michigan.
"The area it was found in, next to the Missouri River, may provide a favorable microclimate for overwintering," Johnson says.
Palmer amaranth "is certainly the most formidable weed that the American grower has ever encountered," says Richard Zollinger, NDSU Extension weed specialist.
It has not yet been found in North Dakota.
"It appears that once established, eradication is impossible -- at least no state or area has been able return the land to 'weed free' status," he says.
Watch for Palmer amaranth while combining corn and soybeans. Remove plants from the field and destroy them, he advises.
See the 2014 Weed Guide for pictures to help you identify the weed, and for more information about controlling it.
Sources: SDSU, NDSU