Efficacy of 2,4-D Choline as Influenced by Weed Size in the Texas High Plains

Aim: Postemergence timing trials based on weed size were conducted near Lubbock, TX to assess the effectiveness of 2,4-D choline + glyphosate on control of Palmer amaranth (Amaranthus palmeri S. Wats.), Russian-thistle (Salsola tragus L.), and kochia (Kochia scoparia L.) at three growth stages (3 to 5 cm, 10 to 15 cm, and 20 to 30 cm).

Study Design: All trials were arranged in a randomized complete block design with four replications.

Place and Duration of Study: Field experiments were conducted in 2013, 2014, and 2015 in Lubbock, TX at the Texas A&M AgriLife Research and Extension Center near Lubbock, TX.

Methodology: Herbicide treatments consisted of a single postemergence application of 2,4-D choline + glyphosate at two rates, 2,4-D choline + glyphosate at two rates + glufosinate, 2,4-D choline + glyphosate + S-metolachlor, 2,4-D choline + glyphosate + acetochlor, 2,4-D choline + glufosinate, glyphosate, or glufosinate.

Results: The greatest level of weed control for all three weed species was achieved at the 3 to 5 cm timing; however, weed size was most critical for Palmer amaranth and Russian-thistle compared to kochia. Averaged over all three years, Palmer amaranth control decreased from 93 to 74% when evaluated 21 days after treatment following applications that included 2,4-D choline when applied to plants 3 to 5 and 10 to 30 cm, respectively. For Russian-thistle, control decreased from 98 to 78% when evaluated 21 days after treatment following treatments that included 2,4-D choline when applied to plants 3 to 5 and 10 to 30 cm, respectively. For kochia, control decreased from 98 to 84% when evaluated 21 days after treatment following treatments that included 2,4-D choline when applied to plant 3 to 5 and 10 to 30 cm, respectively.