Impact of Cotton Weed Management Practices on Palmer Amaranth Populations in Year Three of a Long-Term Study.

In United States' cropping systems, Palmer amaranth has become one of the most troublesome weeds, particularly in slow canopying crops such as cotton. A long-term field trial was initiated at the University of Arkansas System Division of Agriculture's Lon Mann Cotton Research and Extension Center, Marianna, Arkansas, to assess the impact of cultural and mechanical weed management strategies on Palmer amaranth over a three-year period. Non-chemical approaches such as tillage, cover cropping with cereal rye, and zero-tolerance were evaluated in combination with two standard weed control systems, one with dicamba used preemergence (PRE) and early postemergence (POST) compared to a program with no dicamba herbicide. The experiment was organized in a randomized complete block design with 16 treatments and four replications. Results showed that adopting a cover crop reduced weed emergence by 82%. The use of the zero-tolerance approach plus dicamba and non-dicamba herbicides showed comparative results, both causing a 63% reduction in Palmer amaranth emergence. A 37% reduction was observed in treatments that included tillage, but statistically, no difference was observed compared to treatments lacking tillage. The adoption of zero-tolerance with dicamba and non-dicamba herbicides plus the use of a cover crop (cereal rye) had a high impact on reducing the number of Palmer amaranth seedlings emerging throughout the trial. In the battle against herbicide resistance, the combination of multiple weed control practices (chemical, cultural, mechanical, and others) is essential to manage resistant weed populations and maintain sustainable cotton production. [ABSTRACT FROM AUTHOR]