Recently, we have identified populations of Palmer amaranth in several Illinois counties. The density of many populations is relatively low, and often these plants occur only in small patches. However, a few scattered plants this year can lead to severe infestations within only a few years.
We continue to accept tissue samples from suspected Palmer amaranth plants and use tools of molecular biology to identify whether the sample is Palmer amaranth or another species of Amaranthus. Information on how to collect and submit tissue samples from suspected Palmer amaranth plants can be found in the “Palmer Amaranth Identification” form that accompanies this article.
So, what should you do if you discover Palmer amaranth growing in your fields? We have developed the following suggested guidelines and also have made these available in a format that can be downloaded and printed. Keep in mind these guidelines assume a scenario where the population of Palmer amaranth is only a few plants per acre:
1) If you discover a plant that you think may be Palmer amaranth, you can verify its identity by sending a leaf tissue sample to the University of Illinois (please find a sampling protocol in the Palmer amaranth ID form accompanying this article) for identification using molecular biology techniques.
2) Plants confirmed or suspected of being Palmer amaranth should be physically removed from the field prior to flowering. Do not rely on herbicides for control. Physical removal can include hoeing or hand-pulling plants from the soil. If hoeing is used, be sure to sever the plant stem at or below the soil surface to reduce the potential for regrowth, and remove plants from the field as they will re-root from stem fragments.
3) If Palmer amaranth plants are not identified until after brown-to-black colored seeds are present on female plants, we suggest leaving the plants undisturbed in order to avoid inadvertently spreading seed.
4) Mark or flag areas where Palmer amaranth plants produced seed. These areas should be intensively scouted the following season and an aggressive Palmer amaranth management plan implemented to prevent future seed production.
5) Do not mechanically harvest mature Palmer amaranth plants. Physically remove the plants prior to harvest and either leave the plants in the field or place in a sturdy garden bag and remove the plants from the field. Bury or burn the bags in a burn barrel as soon as possible.
6) Fields in which Palmer amaranth seeds were produced should NOT be tilled during the fall or following spring. Leaving the seeds near the soil surface increases the opportunities for seed predation by various granivores.
7) Herbicides that control waterhemp also control Palmer amaranth. An integrated herbicide program should include soil-residual herbicides applied at full recommended use rates of within two weeks of planting and followed by postemergence herbicides applied before Palmer amaranth plants exceed 3 inches tall.
And remember, fields containing Palmer amaranth should be the last fields harvested in 2013 and the last fields planted in 2014.