Integration of Multiple Weed Management Practices on Cotton Economics and Palmer Amaranth (Amaranthus palmeri) Populations


 The threat of herbicide-resistant weed species, such as Palmer amaranth, has driven the development of robust weed management programs that rely on more than chemicals for weed control. Previous research has shown that the use of a zero-tolerance weed thresholds, cover crops, deep-tillage, and diverse herbicide programs are all effective strategies for controlling Palmer amaranth. Unfortunately, research investigating the integration of all four of these weed management strategies in a system is lacking. To better leverage these integrated weed management strategies in cotton production systems, a long-term study was initiated in the fall of 2018 near Marianna, AR, with zero-tolerance, deep-tillage, a cereal rye cover crop, and either a dicamba or non-dicamba in-crop herbicide program as factors. Results found that total Palmer amaranth emergence was reduced 76% as the result of deep tillage in 2019 and, in the absence of a zero-tolerance strategy, 73% in 2020. In the absence of a zero-tolerance strategy, the combination of a non-cover crop strategy and dicamba herbicide program decreased total Palmer amaranth emergence by 73% while the combination of a cover crop strategy and dicamba herbicide program decreased total Palmer amaranth emergence by 78% compared to the combination of a cover crop and non-dicamba herbicide program. Under a zero-tolerance strategy in 2019, tillage reduced cotton yield by 12% and partial returns by $370 ha-1. In 2020, tillage reduced cotton yield by 14% and partial returns of $371 ha-1 under a non-zero-tolerance strategy while a 12% yield reduction and $260 ha-1 decrease in partial returns was observed under a zero-tolerance strategy. In 2019, the non-dicamba program resulted in greater partial returns than the dicamba in-crop program because of greater yield and lower program costs. However, in 2020 partial returns were greater for the dicamba in-crop herbicide program due to greater yields achieved by this program.