Minnesota Department of Agriculture Confirms Palmer Amaranth in Goodhue County

St. Paul, MN: The Minnesota Department of Agriculture (MDA) has positively identified the invasive weed Palmer amaranth in Goodhue County.

After a crop consultant reported a suspected plant to the MDA, staff conducted a site visit and found the weed in two corn fields managed by one farmer. The MDA scouted fields surrounding the documented infestations and did not find any additional Palmer plants. It is unknown at this time how Palmer amaranth got into the two fields; however, the MDA is continuing to investigate potential sources.

An herbicide application stunted but did not kill the plants. A crew hand pulled weeds in the two fields to eliminate any chance of seed production. The MDA will continue to work with the farmer, crop consultants, U of M Extension, and the County Agricultural Inspector to manage these infestations.

"This is a good example of the limits of herbicide on Palmer amaranth," said Denise Thiede, MDA's Seed Unit Supervisor. "If plants are allowed to reach a certain size, an herbicide application may not control them. That's why we're counting on farmers and crop consultants to report suspected plants. They are our best line of defense against Palmer amaranth."

The MDA is asking farmers and agronomists to take photos of suspicious plants, pull them out, and save them in plastic bags for genetic testing if needed. Report the find to the Minnesota Department of Agriculture's Arrest the Pest line at 1-888-545-6684 or arrest.the.pest@state.mn.us.

Palmer amaranth can be identified by the following characteristics:

• The green leaves are smooth and arranged in an alternate pattern that grows symmetrically around the stem. The leaves are oval to diamond or triangle shaped.

• The leaves of some Palmer amaranth plants have a whitish, V-shaped mark on them. Not all Palmer amaranth plants display this characteristic.

• Palmer amaranth looks similar to our native pigweeds such as waterhemp ( tuberculatus and A. rudis), Powell's amaranth (A. powellii), and redroot and smooth pigweeds (A. retroflexus and A. hybridus, respectively). Here are some distinguishing characteristics:

o Redroot and smooth pigweeds have fine hairs on their stems and leaves. Palmer amaranth and waterhemp do not have these hairs.

o The petiole (stalk connecting a leaf to the stem) is longer than the length of the leaf. For waterhemp, the petiole will be only half the length of the leaf.

o Seedhead spikes on female Palmer amaranth plants are much taller (up to three feet long) and pricklier than waterhemp or redroot and smooth pigweed spikes.

Photos and other information on Palmer amaranth can be found on the MDA website at http://www.mda.state.mn.us/palmeramaranth.

Palmer amaranth is listed as a noxious weed in Minnesota and was first discovered in the state in 2016. All above and below ground parts of the plant must be destroyed, and it cannot be moved. The invasive weed is also listed as a prohibited weed seed in the state. This means no Palmer amaranth is allowed in any seed offered for sale in Minnesota.

Palmer amaranth has been found in 11 Minnesota counties, including Goodhue County. However, most of the sites have been successfully eradicated and the remaining are being closely monitored. Details of previous finds can be found on the MDA website.

Left uncontrolled, a single female Palmer amaranth plant typically produces 100,000 to 500,000 seeds. It is resistant to multiple herbicides, can cause substantial yield losses, and greatly increase weed management costs in soybeans and corn.