When Needs Drive Solutions: New Test for Palmer Amaranth

- Toni Bartling

What’s the most troublesome weed in the United States? According to the Weed Science Society of America, Palmer amaranth, also known as Palmer pigweed, takes the prize. Growing 2-3 inches per day, it can have a devastating impact on crop yields. Its stems are tough enough to damage rugged farm equipment and it’s extremely prolific — a single plant can produce as many as a million seeds during the growing season.

According to the U.S. Department of Agriculture, yield losses up to 91 percent in corn and 79 percent in soybeans in the Midwest have been found.

As such, a number of states have proposed the addition of Palmer amaranth to their noxious weeds list, and this proposed change was approved in Delaware, Minnesota and Ohio. However, no seed test could identify Palmer amaranth from other amaranth species in a seed lot.

Minnesota has a zero-tolerance policy, meaning that if any Palmer amaranth is found in a seed lot, it cannot be sold in the state. In 2016, our seed testing team began working with the Minnesota Department of Agriculture, who funded the research, to develop a genetic test. This proved no easy task as we had to be able to extract enough DNA to test, and Palmer amaranth seed is very small.

With the help of Robert Price, senior seed botanist with the California Department of Food and Agriculture Plant Pest Diagnostics Branch, we developed a test that uses DNA sequencing and analysis of internal transcribed spacer (ITS) region that allows us to identify individual Palmer amaranth seeds in a seed lot. Price had been using ITS sequencing in his laboratory to identify fungal diseases.

First, we recommend growers us a purity noxious test to sort out any noxious weed seeds that might be Palmer amaranth. Then we use ITS sequencing to test if the seed is Palmer amaranth.

If Palmer amaranth is confirmed, then it must be marked on the report, and that seed cannot be sold in the state. However, if no Palmer amaranth is found, we can amend the report and the customer can sell their seed.

To meet future needs, we are working to develop a PCR-based assay to identify Palmer amaranth. This would make it less expensive and allow for a quicker turnaround time. Additionally, laboratory technicians could test a pool of seeds compared to testing each seed individually.