Managing herbicide-resistant waterhemp (Amaranthus tuberculatus [Moq.] J.D. Sauer) seedbanks by integrating several management tactics

Abstract

Herbicide-resistant waterhemp (Amaranthus tuberculatus [Moq.] J.D. Sauer) continues to threaten the productivity of many US crops. Thus, integrating non-herbicidal tactics with herbicides to reduce weed seedbanks is gaining popularity. A field study was conducted near Logan, IA from fall 2021 to fall 2022 to evaluate the impacts of cereal rye (Secale cereale L.) cover crop, herbicides, and harvest weed seed destruction on the waterhemp seedbank inputs. The cereal rye cover crop reduced waterhemp seed production by 90% compared to treatments without the cereal rye cover crop, while herbicides did not significantly affect waterhemp seed production. Furthermore, 96% of waterhemp seeds that entered the combine at harvest were destroyed and seed destruction effectiveness was not affected by cereal rye cover crop, herbicide program, or combine speed. Thus, cover crops and weed seed destruction are effective tactics to minimize waterhemp seedbank inputs. Waterhemp seed retention and combine header losses of waterhemp seeds were evaluated at harvest. Waterhemp seed retention was not affected by the cereal rye cover crop or herbicide programs. Only 30% of waterhemp seeds remained on the plant at harvest; the likely causes of seed shattering were late harvest and windy conditions prior to harvest. Waterhemp seed shattering from the combine header averaged 2.6% and was not affected by cover crop, herbicide program, or combine speed. These results support the inclusion of non-herbicidal control tactics to reduce herbicide-resistant waterhemp seedbanks and suggest the need for future research to optimize weed seed destruction.