WEST LAFAYETTE, Ind. — As Midwest farmers tend to their fields and prepare for another season, they do so with a wary eye. It isn’t herbivorous critters or gnawing bugs that worry growers, but instead a noxious weed.

 

Palmer amaranth, which is scientifically known as Amaranthus palmeri, is resilient and invasive. It is the culprit attributing to the destruction and loss of cash crops across the much of the country. A report published by the USDA said Palmer amaranth was recently found as a contaminant to conservation planting plots in Illinois, Indiana, Iowa, Minnesota and Ohio.

“(Palmer amaranth) has given us a big headache in the Midwest, but here it is not as bad as in the southern United States,” said Bill Johnson, a professor of weed science at Purdue University. “I have heard of farmers in the South who have had to mow down whole fields.”

The USDA report went on to say that Palmer amaranth could become a major agronomic problem in the western United States and Midwest if something is not done to curb its spread. 

 

Not native to the Midwest, the weed originates from the desert Southwest and northern Mexico, according to the USDA.

“Palmer amaranth has been documented in the United States for the last 50-60 years,” said Aaron Hager, a University of Illinois crop science professor. “It has become a problem within the last 10 years.”

In 2016, the Des Moines Register reported that Iowa had confirmed accounts of Palmer amaranth in 49 counties. Johnson said Palmer amaranth has been found in 40 of Indiana’s 92 counties. He added that dry growing seasons help spread the weed. Johnson said yield loss depends largely on plant density within an impacted field, but usually ranges between a 10-80 percent loss. According to Hager, the primary reason for the weed’s rapid seizure of farmland is the long-distance transport of seed.

Seeds are transported by air, animals, farm equipment and through trade. Each plant can produce 100,000-500,000 seeds, which can survive 5-7 years.

The USDA advises that pulling the weed before it starts to develop seeds is effective in halting its spread. Hager explained that field entrances are more susceptible to infestation because equipment carries seeds to these areas the most. “(Palmer amaranth) moves no matter what,” Hager said. “It is best to pull all traces of the weed from fields as early as possible.”

Hager said there can be little or no cost in managing Palmer amaranth if farmers are annually active in combating it. However, he knows that when uncontrolled, it can put a farmer out of business. 

 

Hager admits herbicides work against Palmer amaranth, but said farmers need to be aware the weed grows resistant to herbicides. A Purdue University report published, in part by Johnson, said individual Palmer amaranth plants are either male or female, which forces outcrossing and genetic diversity. This gives the weed the ability to spread herbicideresistant genes when extermination measures are taken by farmers.

Palmer amaranth can grow between 6-7 feet tall by maturity and does so at a rate of 1 inch in height per day, according to a time-lapse study conducted by Purdue University. However, some plants can achieve a growth rate of 2-3 inches per day. The USDA said plants emerge in the Midwest in May and last through September.

“It is certainly the worst one I have encountered,” said Hager when asked if Palmer amaranth is the worst weed ever to plague farmland and cash crops. “The effects of Palmer amaranth can be devastating and farmers can’t ignore it.”