Evaluation of Adjuvants on Flumioxazin Efficacy for Postemergence Annual Bluegrass and Residual Smooth Crabgrass Control

Abstract

Flumioxazin is a protoporphyrinogen oxidase (Protox) inhibitor with potential for postemergence (POST) control of annual bluegrass (Poa annua L.) and preemergence (PRE) control of smooth crabgrass [Digitaria ischaeum (Schreb.) Schreb. ex Muhl.] in bermudagrass [Cynodon dactylon (L.) Pers.]. However, flumioxazin efficacy is reduced under low temperatures, and control is often inconsistent on mature annual bluegrass. The objective of this research was to evaluate the use of adjuvants on flumioxazin efficacy for POST control of annual bluegrass and residual smooth crabgrass in bermudagrass. Tank-mixing methylated seed oil, nonionic surfactant, or ammonium sulfate did not improve POST annual bluegrass control from flumioxazin at 0.42 kg active ingredient (a.i.) ha⁻¹ alone. Granular urea antagonized flumioxazin efficacy and increased the time to achieve 50% annual bluegrass control (C₅₀) by more than 4 weeks. Flumioxazin alone controlled annual bluegrass >80% at 9 weeks after treatment in both years. All treatments provided excellent (90 to 100%) control of smooth crabgrass at 4 months after treatment (MAT) and ≥89% control at 5 MAT. All flumioxazin treatments provided >70% control of smooth crabgrass and reduced grid count cover >65% from the untreated at 7 MAT. Although adjuvants did not enhance speed of annual bluegrass control from late-winter applications, flumioxazin alone controlled annual bluegrass >80%, and provided >80% PRE control of smooth crabgrass.