Abstract
AbstractProper management of glufosinate in glufosinate-resistant crop technologies is needed to mitigate the likelihood of resistance evolution. Antagonism may result from mixtures of glufosinate and other commonly used POST herbicides in soybean and cotton. Two experiments were conducted at the Arkansas Agricultural Research and Extension Center in Fayetteville, AR, in 2015 and 2016 to evaluate mixtures of glufosinate + clethodim and glufosinate + glyphosate on barnyardgrass, broadleaf signalgrass, johnsongrass, and large crabgrass. Furthermore, droplet spectra analyses were conducted to determine if droplet size was associated with identification of herbicide interactions. Antagonism was dependent on the herbicide rates and the weed species. For barnyardgrass and large crabgrass control 4 wk after treatment, glufosinate + glyphosate was antagonistic at all rates evaluated. When large crabgrass was evaluated, some mixtures (e.g., 595 g ha–1 glufosinate + 76 g ha–1 clethodim) had a significant reduction in control relative to one of the herbicides applied alone. Glufosinate (451 and 595 g ai ha–1) + glyphosate (867 and 1,735 g ae ha–1) was antagonistic at all four possible rate combinations for broadleaf signalgrass control. Fewer instances of antagonism were observed for seedling johnsongrass control than for other species, but certain treatments were identified as antagonistic (e.g., glufosinate at 451 g ai ha–1 + clethodim at 76 g ai ha–1). Overall, antagonism was less likely and greater control was observed when the highest rates of both herbicides in a given mixture were used. The addition of glyphosate or clethodim to glufosinate can increase the volume median diameter and decrease the percentage volume of fines, compared to glufosinate alone. The droplet spectra analyses indicate that the glufosinate performance may be negatively affected by the addition of glyphosate or clethodim.
Highlights
The addition of S-metolachlor to glufosinate at 451 g ha–1 improved control from 88% to 94% despite S-metolachlor having no measurable POST activity
Applications of mixtures will be needed in most farmer fields to control a broad spectrum of weeds, with some species resistant to glyphosate. These results suggest that if glufosinate is to be applied to a field with large crabgrass, glyphosate should be added to glufosinate instead of clethodim, if the crop technology allows (e.g., Glytol® LibertyLink® cotton)
In the case of large crabgrass, glufosinate þ glyphosate may be better than glufosinate þ clethodim from a resistance management perspective, because the performance of the mixture is less likely to be reduced relative to the systemic herbicide alone across a range of rates
Summary
Glufosinate at 451 g ha–1 þ clethodim at g ha–1 was antagonistic for both percent control (91% observed vs 99% expected) and biomass reduction (Table 2). The combination of glufosinate at 451 g ha–1 þ clethodim at g ha–1 had improved control and biomass reduction over either component of the mixture alone (Table 4).
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