Effect of dicamba rate and application parameters on protoporphyrinogen oxidase inhibitor-resistant and -susceptible Palmer amaranth (Amaranthus palmeri) control

Abstract

Throughout eastern Arkansas, Palmer amaranth resistant to protoporphyrinogen oxidase (PPO)-inhibiting herbicides (Group 14) has become widespread. Most PPO-resistant Palmer amaranth biotypes possess a target-site mutation, but a metabolic resistance mechanism to fomesafen (Group 14) has also been identified. Once metabolic resistance manifests, plants may also be tolerant to other herbicides and sites of action. To evaluate whether varying spray parameters affected control of PPO-resistant Palmer amaranth in dicamba-tolerant crops, field trials were conducted in 2017 and 2018 at the Lon Mann Cotton Research Station near Marianna, AR, and on-farm in Marion, AR. The experiment included split plot factors of dicamba rate, nozzle type, and carrier volume, with a whole plot factor of population. Dicamba was applied at 560 or 1120 g ae ha-1 through 110015 TTI or AirMix nozzles at 70 or 140 L ha-1 to PPO-resistant or PPO-susceptible Palmer amaranth. Palmer amaranth control 14 days after treatment (DAT) was influenced by an interaction between population and carrier volume. PPO-resistant Palmer amaranth control 14 DAT was 81% regardless of carrier volume, compared to 90% and 95% control at 70 and 140 L ha-1, respectively, of the PPO-susceptible population. An interaction between nozzle type and carrier volume influenced Palmer amaranth control 21 DAT, where AirMix nozzles at 140 L ha-1 controlled Palmer amaranth at a greater level (94%) than any other nozzle and carrier volume combination (≤90%). An interaction between population and dicamba rate influenced Palmer amaranth relative density 21 DAT. PPO-resistant Palmer amaranth density was less affected by dicamba at either rate than PPO-susceptible Palmer amaranth, relative to the nontreated check. Results concur with those of other research that suggest PPO-resistant Palmer amaranth is harder to control with dicamba. Otherwise, increasing carrier volume affected overall Palmer amaranth control to a greater degree than any other factor.

Effect of single or sequential POST herbicide applications on seed production and viability of glyphosate-resistant Palmer amaranth (Amaranthus palmeri) in dicamba- and glyphosate-resistant soybean

“…At soybean harvest, a single application of dicamba at V4 or sequential applications reduced Palmer amaranth density as low as 2 or fewer plants m −2 compared with 5 or fewer plants m −2 with dicamba in a single application at R1 (Table 3). Similarly, Coffman et al (2020) reported Palmer amaranth densities of 7% and 19% of the nontreated control 21 d after dicamba application at 560 g ae ha −1 . The PPO inhibitors acifluorfen, lactofen, or fomesafen and fluthiacet applied in a single application at early SGS or in sequential applications were usually comparable and reduced Palmer amaranth density to not more than 15 plants m −2 .…”

Amaranthus hybridus L. RESISTANT TO GLYPHOSATE AND CHLORIMURON IN PARAGUAY

“…The association of cover crops with herbicides in the integrated management of A. hybridus was also effective (Bunchek et al, 2020). Coffman et al (2021) observed that the application of dicamba could be an alternative for the control of the PPO-resistant A. palmeri; however, lower levels of control were observed in the PPO-resistant population than in the susceptible population. Other studies have reported the use of glufosinate to control Amaranthus spp.…”

Utility of roller wiper applications of dicamba for Palmer amaranth control in soybean

“…Combinations of glyphosate and dicamba controlled 90% to 100% of glyphosate‐resistant waterhemp, Palmer amaranth, and horseweed 8 . Applications of dicamba in dicamba‐resistant cotton controlled 88% to 90% of protoporphyrinogen oxidase (PPO)‐resistant Palmer amaranth in Arkansas at 21 days after treatment (DAT) 9 . Growers in Nebraska reported that the addition of dicamba to soybean herbicide programs resulted in improved weed control for 93% of growers surveyed 10 .…”

“…8 Applications of dicamba in dicamba-resistant cotton controlled 88% to 90% of protoporphyrinogen oxidase (PPO)-resistant Palmer amaranth in Arkansas at 21 days after treatment (DAT). 9 Growers in Nebraska reported that the addition of dicamba to soybean herbicide programs resulted in improved weed control for 93% of growers surveyed. 10 Concurrent with the commercialization of dicamba for in-crop use over soybean in 2016, there was an increase in complaints for auxin damage on non-dicamba resistant soybean.…”