Assessing forage bermudagrass cultivar tolerance to glyphosate application

摘要

Abstract In‐season weed control with glyphosate could be a feasible option if bermudagrass [Cynodon dactylon (L.) Pers.] tolerance to glyphosate was better understood. The objective of this study was to evaluate the tolerance of bermudagrass cultivars ‘Goodwell’ and ‘Greenfield’ to varying glyphosate rates under controlled environment. The experimental design was a factorial arrangement in a completely randomized design (CRD) with the two forage bermudagrass cultivars and the five glyphosate application rates (0.35, 0.47, 0.95, 1.37, and 2.75 lb a.i. ac−1) plus the nontreated control. Visual injury (VI) was collected at 8, 16, and 24 days after glyphosate application (DAG), and dry matter regrowth relative to nontreated control (%DMRrel) was measured at 56 DAG. Results indicated that VI developed faster in Goodwell until 8 DAG, but both cultivars had similar glyphosate VI at its peak (16 DAG). Although glyphosate VI was similar in both cultivars at 16 and 24 DAG, Goodwell showed greater %DMRrel at glyphosate rates ≥0.95 lb a.i. ac−1 than Greenfield at 56 DAG. Moreover, the prediction of %DMRrel from previous canopy VI followed distinct negative exponential relationships for each cultivar‐DAG combination. The Akaike Information Criterion (AICc) numerical differences were negligible when comparing relationships at different DAGs for a specific cultivar. Practically, VI readings taken at any evaluated DAGs were considered appropriate for estimating %DMRrel. Results suggested that bermudagrass glyphosate tolerance is cultivar‐dependent, where Goodwell showed improved tolerance allowing in‐season glyphosate application to control weeds at higher rates than Greenfield. Studies at field conditions must be performed to validate our findings.