In September 2016, Palmer amaranth, Amaranthus palmeri, was initially discovered and confirmed in Minnesota. To date, isolated populations have been documented in first year conservation plantings in Yellow Medicine, Lyon, Douglas and Todd Counties. The Minnesota Department of Agriculture (MDA), University of Minnesota Extension, USDA, landowners and other partners are working to eradicate these infestations before they can spread to new areas. Efforts to this point have been very successful. MDA is also working closely with other state, county and federal agencies, the MN Native Seed Industry and several non-profit organizations to regularly sample and test seed sold in the state for presence of Palmer amaranth.
Why the concern?
- Palmer amaranth is a fast growing weed native to the southwestern United States and northwestern Mexico, and has spread east and north through a variety of pathways including contaminated seed, hay, livestock feed and agricultural equipment. It has developed resistance to multiple classes of herbicides and their different modes of action, making it very difficult and expensive to control. Palmer amaranth is a prolific seed producer. Up to 250,000 seeds can come from one plant. It is also highly competitive.
- It has a fast growth rate of 2- 3 inches per day and commonly reaches heights of 6- 8 feet, greatly inhibiting crop growth. Reported yield losses have been up to 91% in corn and 79% in soybean in some states. The weed can also significantly increase production costs for corn, soybean, and other crops.
What is the weed's legal status in Minnesota?
- Since 2014, Palmer amaranth has been listed on Minnesota’s Prohibited Noxious Weed Eradicate List. All above and below ground parts of the plant must be destroyed. Additionally, no transportation, propagation, or sale of this plant is allowed. Failure to comply may result in enforcement action by the county or local municipality. More info on noxious weeds can be found on the MDA website.
- In November 2016, the Commissioner of Agriculture listed Palmer amaranth as a Prohibited Weed Seed. This means no Palmer amaranth seed is allowed in any seed offered for sale in the state. This includes agricultural, vegetable, flower, tree, shrub, native grass, and forb seeds sold in Minnesota. Visit the MDA's website for more information on seed regulations in Minnesota.
What can you do?
- Be proactive and prevent Palmer amaranth establishment. Familiarize yourself with Palmer amaranth identification and actively look for it in crop fields, borders, ditches, conservation lands and around dairies.
- If you suspect Palmer amaranth on your property, immediately call your local U of M Extension Educator or IPM Specialist, crop consultant and/or the MDA’s Arrest the Pest (888-545-6684) to report locations.
- AVOID entering areas where Palmer is suspected or confirmed. If you must enter an infested area, always clean vehicles, equipment, and clothing prior to exiting.
- If planting grasses and other flower mixes for conservation plantings, use local sources to ensure plants are compatible with Minnesota’s climate and that they come from a reputable source.
How can you identify Palmer amaranth?
- Palmer amaranth is a summer annual that commonly reaches heights of 6- 8 feet but, can reach 10 feet or more.
- The green leaves are smooth and arranged in an alternate pattern that grows symmetrically around the stem. The leaves are oval to diamond-shaped. There may be a small, sharp spine at the leaf tip.
- The leaves of some Palmer amaranth plants have a whitish V-shaped mark on them. Not all Palmer amaranth plants display this characteristic.
- There are separate male and female plants.
- Palmer amaranth looks similar to our native pigweeds such as tall waterhemp (A. tuberculatus), redroot and smooth pigweeds (A. retroflexus and A. hybridusrespectively). Here are some distinguishing characteristics:
- Redroot and smooth pigweeds have fine hairs on their stems and leaves. Palmer amaranth and waterhemp do not have these hairs.
- The petiole (stalk connecting a leaf to the stem) is longer than the length of the leaf. For tall waterhemp, the petiole will be only half the length of the leaf.
- Seedhead spikes on female Palmer amaranth plants are much taller (up to 3 feet long) and more prickly than waterhemp or redroot and smooth pigweed spikes.
For more information:
- Identifying Palmer amaranth in the field video
- Minnesota Extension: Minnesota Crop News - IPM Weeds
- Purdue Extension: Palmer amaranth biology, identification and management
- Iowa State University: Palmer amaranth, ID, biology and management