Managing Palmer Amaranth (Amaranthus palmeri) with Sequential Applications of Glufosinate and 2,4-D

Aims: Determine the influence of sequential spray order and role of glufosinate when used in a system with 2,4-D to control Palmer amaranth at two different growth stages.

Study Design: Randomized complete block design with three replications.

Place and Duration of Study: A fallow, non-crop field at the Texas A&M AgriLife Research and Extension Center, Lubbock, Texas, during the 2018 and 2019 growing seasons.

Methodology: Herbicides were applied to 7 to 15 cm and 25 to 30 cm Palmer amaranth with a handheld 1.93m CO2-pressurized backpack calibrated to deliver 140 L ha-1 at 207 kPa. Palmer amaranth control was visually estimated on a scale of 0 (no control) to 100% (complete control) relative to the nontreated control. Palmer amaranth biomass and density were collected 43 and 36 days after the last sequential application for 7 to 15 cm and 25 to 30 cm Palmer amaranth in 2019. Palmer amaranth control, biomass, and density were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at P=.05.

Results: 2,4-D choline + glyphosate followed by glufosinate provided the greatest level of Palmer amaranth control for both sizes of Palmer amaranth. Overall, Palmer amaranth control was not influenced by sequential application timing. Biomass and density were not significantly different among treatments.

Conclusion: Sequential application order of glufosinate and 2,4-D was not an important factor for Palmer amaranth control. However, due to 2,4-D label restrictions, applying 2,4-D choline + glyphosate followed by glufosinate may be the best option for maximum efficacy.