Evaluation of Application Placement and Adjuvants On Flumioxazin Efficacy for Controlling Annual Bluegrass and Crabgrass.

Greenhouse experiments were conducted to evaluate the effect of application placement on flumioxazin efficacy for annual bluegrass (Poa annua) and large crabgrass (Digitaria sanguinalis). Treatments of flumioxazin were applied foliar-only, soil-only, or foliar-plus-soil at rates of 0.21, 0.42, and 0.84 kg ai ha^-1.  Flumioxazin caused the greatest injury to annual bluegrass and large crabgrass with soil-only and foliar-plus-soil applications. Soil-only and foliar-plus-soil applications had comparable efficacy and shoot mass reductions for these applications were greater than 60% for all rates. Foliar-only applications caused significantly less injury to both species at all rates. Field experiments were conducted to investigate flumioxazin efficacy with various adjuvants for postemergence annual bluegrass control in dormant bermudagrass (Cynodon dactylon) and preemergence control of crabgrass.  Flumioxazin works best for early postemergence annual bluegrass control, but efficacy may be enhanced with adjuvants on mature annual bluegrass and provide greater residual crabgrass control. Applications were made in February of 2012 and 2013 during a time of typically limited flumioxazin efficacy. Flumioxazin was evaluated at a rate of 0.42 kg ai ha^-1 alone, or in combination with one or more of the following adjuvants: nonionic surfactant (0.25% v/v), methylated seed oil (1.00% v/v), ammonium sulfate (8.97 kg ha^-1), and granular urea (73.24 kg ha^-1). Flumioxazin treatments with ammonium sulfate or urea alone did not provide greater control of annual bluegrass in the same amount of time as flumioxazin alone. In general, the treatments to provide 50% annual bluegrass control rapidly were those that included methylated seed oil.  All flumioxazin treatments provided >80% crabgrass control five months after treatment.