Herbicide resistance in Amaranthus palmeri
Amaranthus palmeri (Amaranthaceae - EPPO A2 List) is a dioecious summer annual species native to North America. In its native range, it is a weed in agricultural fields and disturbed habitats. It has a high fecundity and a long-lived seed bank, which make management of the species difficult. In the EPPO region, it is established in a few countries and transient in several others. A. palmeri can develop resistance to herbicides which can complicate the management of the species (see EPPO RS 2021/095). In South Africa, A. palmeri is classified as naturalized. A population of A. palmeri was found in the Douglas district in South Africa and showed resistance to herbicides with different sites of action. Initially, this A. palmeri population was discovered in a glyphosate- tolerant cotton field, where it survived glyphosate treatment. Greenhouse experiments and molecular analyses indicated resistance to chlorimuron-ethyl and glyphosate, while <90% control was observed at the label rate for mesotrione, atrazine, saflufenacil, and S-metolachlor. However, glufosinate, tembotrione, acifluorfen, dicamba, 2,4-D, metribuzin, acetochlor, isoxaflutole, diflufenican, and pyroxasulfone were effective at controlling the population. This type of profiling of herbicide sensitivity can allow for the development of programmes to control and potentially minimize the spread of this weed.
Sources
Reinhardt C, Vorster J, Küpper A, Peter F, Simelane A, Friis S, Magson J, Aradhya C (2022) A non native Palmer amaranth (Amaranthus palmeri) population in the Republic of South Africa is resistant to herbicides with different sites of action. Weed Science. https://doi.org/10.1017/wsc.2022.9