Evaluation of the summer slump application of saflufenacil on nondormant conventional alfalfa

Abstract

AbstractAlfalfa (Medicago sativa L.) is an important crop for the low desert region of southwestern United States. A field study was conducted to evaluate tolerance of established nondormant conventional alfalfa to saflufenacil applied during the summer slump. Treatments consisted of saflufenacil applied alone at 0.7 or 1.4 oz ac−1, or saflufenacil at 0.7 oz ac−1 tank‐mixed with imazamox, bromoxynil, or metribuzin at 0.8, 6.0, or 16.0 oz ac−1, respectively. Methylated seed oil (as surfactant) and ammonium sulfate (as adjuvant) were tank‐mixed at 1 and 2.5% (v/v), respectively, to each herbicide treatment. At 2 d after treatment, alfalfa injury from saflufenacil at the lower rate was lowest (21%); whereas the injury was highest (48%) from saflufenacil plus bromoxynil treatment. The alfalfa injury progressed for 2 wk after treatment (WAT) and was >36% for all treatments except for saflufenacil at the lower rate. Crop recovery was observed about 2 WAT and minimal injury (<3%) occurred at 4 WAT. Alfalfa height was similar across herbicide treatments and the weed‐free (non‐treated) control. At 4 WAT, average alfalfa height for all treatments was 11 inches or greater. The alfalfa injury observed during the initial weeks did not translate into biomass yield reduction. Accordingly, there was no significant difference in alfalfa biomass yield among the treatments. Overall, alfalfa biomass yield was 0.57 and 0.47 ton ac−1 or greater at 4 WAT (1st cutting) and 8 WAT (2nd cutting), respectively, after herbicide application. Our results illustrate that saflufenacil and its tank‐mix with imazamox, bromoxynil, or metribuzin caused injury to nondormant conventional alfalfa during early weeks, but alfalfa recovered by 2 wk after herbicide application without height and biomass yield reduction.