South Dakota: Now Is the Time to Look for Palmer Amaranth

It’s been close to two years since the first Palmer Amaranth (Amaranthus palmen) was found in South Dakota. Since that first confirmation, there are now four confirmed sites in the state. Now is the time of year to be looking for Palmer Amaranth in your fields.

Palmer amaranth is in the pigweed family and there are a lot of closely related pigweeds that can be confused with it. Common waterhemp is the one that is most commonly confused with Palmer. We also have spiny pigweed, tumble pigweed, smooth pigweed, and redroot pigweed that can be confused with Palmer.

Scouting & Identification

A few keys to look for on Palmer are that some of the petioles (the short stem from the main stem to the leaf) will be a lot longer than the leaf length. Also the area where the stem connects to the petioles will have spines on it. On Palmer the leaf is more cordate (heart shaped) than waterhemp which is more elliptic (oblong). Lastly the head will be long and if female it will also be spiny.

There is no one thing to look for that is a sure sign in all cases the plant is Palmer. It seems like we are more likely to find it in areas that have stress periods. So far we have found it mainly in the central part of the state. Usually, we will find it in sunflower or soybean fields.

Fig. 1. Entire plant. Fig. 2. Spiny seed head.
Fig. 3. Spines on Palmer where the stem connects to the petiole. Fig. 4. Petiole longer than the leaf length.

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Reporting Palmer Amaranth Cases

If you suspect you have Palmer Amaranth, start by taking pictures to have it identified. Pictures of the whole plant, of the leaf and petiole area, and also the stem and petiole area, and a picture of the seed head are needed for identification. Email the pictures to Paul Johnson. Make sure to send the highest resolution picture possible as it will help with the identification. Please include the best contact information to return the identification or ask more questions.For more information contact Paul Johnson 605.688.4591.