Tools of the Trade: Be on the look out for Palmer amaranth

September 29, 2016 / by MN Soybean Director of Research David Kee Categories: David Kee, Minnesota Soybean Research & Promotion Council, Soybean News

Palmer amaranth (Amaranthus palmeri) has been found in Yellow Medicine County in a conservation planting. It is a very competitive, warm season, annual broadleaf weed native to the southwestern United States. It is extremely heat and drought tolerant, thus a real problem in the drought prone areas of the U.S. However, its potential effect on Minnesota crops, especially soybeans, is still unknown.

In areas where it persists, Palmer amaranth has been found to be somewhat resistant to cultivation. Timing is extremely critical for adequate control. It develops resistance to multiple herbicide groups, and is extremely competitive (up to 92 percent yield loss in soybeans). Palmer amaranth grows rapidly during extremely warm (up to 104 degrees Fahrenheit) and drought weather. Early identification is critical for control, however seedlings are difficult to distinguish as Palmer amaranth is frequently confused with Waterhemp and other pigweeds.

What can you do about it on your farm? First answer is scout. Palmer amaranth is not native to Minnesota. Consequently, scouting your entire field may not yield significant information.

Now, while it is wet, do a pickup window survey of recently planted conservation areas, grass buffer strips, roadsides and the like. It may have been a contaminant in the conservation seed.  If discovered in these grassland areas, multiple control options are available.

Once identified, develop a control plan for Palmer amaranth. Control in a conservation area such as a buffer strip or grassed waterway will be dependent on the companion plant species. Work with your local expert to determine your best options. Currently, University of Minnesota Extension recommends extracting Palmer amaranth and disposing of the plant or mowing it down before it goes to seed.

Remember, Palmer amaranth is not a problem weed in Minnesota – yet.

We don’t know if our environmental conditions will allow Palmer amaranth to become a problem. However, in certain conditions, it is a serious weed and prevention will be far more preferable than the cure.

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