Adjuvants Influence Late Winter Applications of Bispyribac-Sodium for Annual Bluegrass Control.

Bispyribac-sodium efficacy for annual bluegrass control in perennial ryegrass generally improves under warm temperatures in spring but use in late winter often provides erratic levels of control.  Applying bispyribac-sodium with adjuvants may enhance efficacy in late winter to extend potential applications timings for annual bluegrass control in turf.  To test this hypothesis, field experiments were conducted in Griffin, GA and Knoxville, TN to investigate the influence of adjuvants on bispyribac-sodium efficacy for annual bluegrass control in overseeded perennial ryegrass fairways.  Late winter bispyribac-sodium applications with and without adjuvants in GA injured turf more than in TN but perennial ryegrass recovered at both locations to less than 10% injury by three weeks after sequential treatments.  In GA, late winter applications of bispyribac-sodium at 74 g a.i./ha controlled annual bluegrass by 65% after six weeks but control increased to 90% when the herbicide was applied  with a non-ionic surfactant or methylated seed oil.  In TN, bispyribac-sodium at 74 g a.i./ha with and without adjuvants provided greater than 90% annual bluegrass control but efficacy was similar across treatments.