The Minnesota Department of Agriculture (MDA) has confirmed Palmer amaranth for the first time in Winona County. The Palmer amaranth plants were found in a soybean field but the source of the infestation is currently unknown. As weed escapes become more obvious in row-crops, NOW is the time to be scouting for Palmer amaranth.
MDA press release can be found here.
Identification characteristics of Palmer amaranth
Early detection and eradication of Palmer amaranth is key in reducing management costs and preventing the rapid spread of this difficult weed. Palmer amaranth is challenging to identify as many of the amaranth species look similar. However, identification is easier as plants enter the reproductive phase of development, which is occurring now through September.
Key characteristics to look for include:
- Rapid growth, plants can reach over 6 feet in unmowed areas, but shorter plants possible.
- Plant is smooth with no hairs on stems or leaves.
- Leaf petiole (the stalk connecting the leaf to the stem) is often longer than the leaf.
- Seed and pollen heads can reach 1 to 3 feet in length, which is longer than other amaranth species.
- The most consistent characteristic is the spiny bracts found on the female seed head.
Sources of contamination
So far in Minnesota, confirmed contamination sources of Palmer amaranth have included:
- native seed/pollinator planting mixtures
- contaminated manure (from contaminated sunflower screenings)
- contaminated cover crop seed
Several contamination sources where Palmer amaranth was confirmed, are still unknown, but numerous other contamination sources exist. A list of common contamination sources includes:
- Contaminated crop / cover crop seed (especially seed produced where Palmer amaranth is common).
- Contaminated equipment.
- Used equipment recently purchased (especially from outside the region).
- Custom farm equipment (especially custom combines).
- Contaminated manure / feed ingredients.
- Sunflower screenings
- Purchased hay and straw
- Any other byproduct feed ingredients produced where Palmer amaranth is more common
- Migratory birds are capable of transporting Palmer amaranth and other weed seeds long distances
Status of Palmer amaranth in Minnesota
An interactive map about the presence of Palmer amaranth throughout Minnesota, including sources of contamination and year of last detection can be found here.
Prompt reporting not only assists the MDA in preventing the rapid spread of Palmer amaranth, but it also helps to identify the source of contamination so that proper screening and educational programs can be rapidly put in place. Several scouting tips include:
- Palmer amaranth has a rapid growth rate and may be noticeably taller than waterhemp and other weeds in the field. This has even been observed following mowing events. However, short plants are also possible.
- Palmer amaranth is biologically very similar to waterhemp. If waterhemp escapes are present, it is more likely that Palmer amaranth escapes will be present as well.
- Pay close attention to areas where sprayer booms may not have been loaded with chemical (i.e. where spraying began within the field), making weed escapes more likely
- Pay special attention to field edges and sprayer skips
- Focus scouting efforts where contamination is more likely, including fields seeded with native plantings or cover crops (especially when seed was produced in southern states where Palmer amaranth is more common). Pay special attention to manured fields if feed ingredients included purchased hay, cottonseed, sunflower screenings, etc.
- In some instances Palmer amaranth has maintained its green color slightly longer into the fall compared to waterhemp. This can be a useful tip in late-season Palmer amaranth scouting efforts.
If you or your crop consultant suspect the presence of Palmer amaranth, the MDA and University of Minnesota Extension (U of MN) suggest the following reporting process:
- Take pictures of the plant(s) in question. Pictures should include clear visibility of the whole plant, a close-up of the leaf and where it attaches to the stem, the flower head, and a leaf with the petiole folded over.
- Contact U of MN Agronomy Extension, or MDA immediately and provide the pictures. Please include a phone number where you can be reached.
- It would be preferred to leave the plants in the field until MDA or U of MN can get to the location to verify the plant and collect genetic material for confirmation. Some Palmer amaranth is fairly straight-forward to identify from pictures, but it is still important to get genetic confirmation. It is also crucial at this stage of Palmer invasion to not be destroying plants on your own without confirmation or notifying the MDA. If plants have already been hand pulled, collect at least five leaf samples from each plant, place in a Ziploc bag, and refrigerate until you contact the U of MN or MDA.
The key to successfully eradicating Palmer amaranth in Minnesota is early detection and reporting. Remember, you are not in trouble for having Palmer amaranth in your field, especially considering the numerous routes of entry. Plus, reporting means that you are not on your own when it comes to managing Palmer amaranth infestations.
The MDA and U of MN Extension are working together with farmers and crop consultants to devise effective plans to manage Palmer amaranth infestations.