Sequential applications of synthetic auxins and glufosinate for escaped palmer amaranth (amaranthus palmeri) control

Authors: BROWNE, FRANCES - Auburn University; LI, STEVE - Auburn University; PRICE, KATILYN - Auburn University; LANGEMEIER, RYAN - Auburn University; SANZ-SAEZ, ALVARO - Auburn University; MCELROY, SCOTT - Auburn University; FENG, YUCHENG - Auburn University; Price, Andrew

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2020
Publication Date: 9/19/2020
Citation: Browne, F., Li, S., Price, K., Langemeier, R., Sanz-Saez, A., Mcelroy, S., Feng, Y., Price, A.J. 2020. Sequential applications of synthetic auxins and glufosinate for escaped palmer amaranth (amaranthus palmeri) control. Agronomy. 10(9):1425. https://doi.org/10.3390/agronomy10091425.
DOI: https://doi.org/10.3390/agronomy10091425

Interpretive Summary: Field and greenhouse studies were conducted to investigate the influence of sequence and timing of synthetic auxins and glufosinate on large Palmer amaranth (Amaranthus palmeri) control. Sequential applications of 2,4-D/dicamba + glyphosate followed by (fb) glufosinate at full label rates 3 or 7 days after initial treatment were used in addition to the reverse sequence with a 7 d interval. Time intervals of 3 or 7 d between applications did not influence Palmer amaranth control. Palmer amaranth was controlled 100% for applications of dicamba + glyphosate fb glufosinate and 2,4-D + glufosinate fb glufosinate 7 days after initial treatment in 2018. However, herbicide performance was reduced due to extended drought conditions and taller plants in 2019 with up to 23% less visual injury. Glufosinate severely inhibited mid-day photosynthesis as compared to dicamba with up to 90% reductions in CO2 assimilation 1 day after initial treatment. In general, Palmer amaranth respiration and stomatal conductance were not affected by herbicides in this study. Applications of dicamba + glyphosate fb glufosinate 7 days after initial treatment was the only treatment shown to hinder Palmer amaranth regrowth with a 52% reduction in leaf biomass as compared to the nontreated control. These data suggest Palmer amaranth infested fields are more likely to be rescued with synthetic auxins fb glufosinate than the reverse order but consistent control of large Palmer is unlikely.

Technical Abstract: Field and greenhouse studies were conducted to investigate the influence of sequence and timing of synthetic auxins and glufosinate on large Palmer amaranth (Amaranthus palmeri) control. Field studies were performed in Henry County, AL where treatments were applied to Palmer amaranth with average heights of 37 and 59 cm in 2018 and 2019, respectively. Sequential applications of 2,4-D/dicamba + glyphosate followed by (fb) glufosinate at full label rates 3 or 7 d after initial treatment (DAIT) were used in addition to the reverse sequence with a 7 d interval. Time intervals of 3 or 7 d between applications did not influence Palmer amaranth control. Palmer amaranth was controlled 100% for applications of dicamba + glyphosate fb glufosinate and 2,4-D + glufosinate fb glufosinate 7 DAIT in 2018. However, herbicide performance was reduced due to extended drought conditions and taller plants in 2019 with up to 23% less visual injury. In order to further investigate Palmer amaranth response to dicamba and glufosinate applied sequentially, a greenhouse study was conducted in 2019 where physiological measurements were recorded over a 35 days period. Treatments were applied to Palmer amaranth averaging 38 cm tall and included dicamba + glyphosate fb glufosinate 7 DAIT, the reverse sequence, and a single application of dicamba + glufosinate + glyphosate. Glufosinate severely inhibited mid-day photosynthesis as compared to dicamba with up to 90% reductions in CO2 assimilation 1 DAIT. In general, Palmer amaranth respiration and stomatal conductance were not affected by herbicides in this study. Applications of dicamba + glyphosate fb glufosinate 7 DAIT was the only treatment shown to hinder Palmer amaranth regrowth with a 52% reduction in leaf biomass as compared to the nontreated control. These data suggest Palmer amaranth infested fields are more likely to be rescued with synthetic auxins fb glufosinate than the reverse order but consistent control of large Palmer is unlikely.