It is close to three years now since the first palmer amaranth (Amaranthus palmeri) was found in South Dakota. Since that time there are about a dozen confirmed sites in the state. Now is the time of year to be looking for palmer.
Palmer amaranth is in the pigweed family and has a lot of close relatives 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 (Figure 1). Also, the area where the stem connects to the petioles will have spines on it (Figure 2). 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 will also be spiny (Figure 3). There is no one thing to look for that is a sure sign in all cases that 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, and usually we will find it in sunflower or soybean fields.
Figure 1. Petiole longer than the leaf length.
Figure 2. Spines on palmer where the stem connects to the petiole.
Figure 3. Spiny seed head.
If you suspect you have palmer amaranth start by taking pictures to have it identified. Take pictures of the whole plant, the leaf and petiole area, the stem and petiole area, and a picture of the seed head (Figure 4). Email the pictures to Paul O. Johnson and make sure to send the highest resolution picture as possible 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 O. Johnson.
Figure 4. Entire plant.