SDSU Pierre Regional Center

Palmer Amaranth Update


Last week we had a very successful meeting on Palmer Amaranth at Onida. Thanks to everyone who took the time to attend.

I had a great partner to work with in Paula Barber, the weed supervisor in Sully County, as well as all the people (FSA, CD’s, etc.) who helped by sharing the meeting flyer. This, along with some great speakers and attendance, really made for an informative meeting.

If you missed the meeting, I am including some highlights. This weed is difficult to positively identify when it is small as it is very similar to the other pigweeds such as redroot pigweed and powell amaranth. However, a key identifying characteristic for palmer amaranth is a long petiole. This is the part of the plant that attaches the leaf blade to the stem. The petiole continues to grow as the plant ages; therefore, this characteristic becomes more obvious as the plant matures. Waterhemp, unlike palmer amaranth, typically, does not have a petiole that is longer than its leaf.

Palmer Amaranth and Waterhemp are the two pigweed species we have in this area that have hairless stems. If hairs are observed on the upper portion of the plant at or after the 4-6 leaf stage, then the plant is not palmer or waterhemp. It is most likely redroot pigweed which has short dense hairs on its stems. Once palmer amaranth develops a seed head it is easier to identify as the seed head can be very long. Palmer amaranth can vary in height, depending on growing conditions and what crop it is competing with. It can be as tall or taller than corn in an irrigated corn field.

Management tactics include pre and post emergent applications of herbicides. Crop rotation is also a good option. It will be easier to control this weed in grassy crops and there are more control options available in these crops. This weed does not germinate as well with reduced light, so crops that provide canopy closure earlier in the season will help reduce emergence. Palmer Amaranth will respond to nitrogen applications, therefore placing fertilizer as opposed to broadcasting could reduce its competitiveness.

Purchasing clean seed from a reliable supplier will be important. If pigweed is listed in a seed sample, a DNA test can be performed to determine if the pigweed is palmer or not. Measures should also be taken to avoid bringing the weed in with hay, feed, manure or on equipment if possible.

I plan to continue to provide opportunities to learn about this weed and hopefully we can slow its spread and possibly eliminate it. If people would like help identifying this weed, they can email pictures to me at ruth. beck@sdstate.edu . The other option is to bag the suspect weed where you find it (if it has seed this will prevent spread) and bring it to our office in Pierre or send it to the SDSU Plant Diagnostic Clinic in Brookings for ID. Extension Calendar:

Emerald Ash Borer, Dr. John Ball at the SDSU Regional Extension Center in Pierre on Monday, April 22 at 7 PM. Call 605-773-8120 for more information.

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