Creeping Bentgrass and Smooth Crabgrass Response to Metamifop at Two Mowing Heights.

Metamifop is a new aryloxyphenoxy propionate (AOPP) herbicide currently being evaluated for annual grass control in cool-seasongrasses and zoysiagrass. Research is being conducted to determine effective rate, turfgrass species tolerance, and grass species controlled. Research was initiated to evaluate creeping bentgrass and smooth crabgrass response at two mowing heights, 0.4 and 4.0 cm. Natural smooth crabgrass infestations in creeping bentgrass were treated in this study. Treatments included: Metamifop at 200 to 800 g ai/ha applied singly and sequentially; and fenoxaprop at 17 g ai/ha applied sequentially on a three week schedule. Fenoxaprop injured creeping bentgrass at 4.0 cm following the first application; however, subsequent applications did not exacerbate injury. No other injury was observed at 4.0 cm. Metamifop at 400 and 800 g ai/ha injured 0.4 cm creeping bentgrass >20% 10 days after treatment. Sequential applications did not exacerbate injury. Metamifop at 200 g ai/ha applied sequentially, metamifop at 400 g ai/ha applied singly or sequentially, and metamifop applied at 800 g ai/ha applied singly controlled smooth crabgrass >80% when mowed at 4 cm. All treatments controlled smooth crabgrass >90% at 0.4 cm. Observations suggest more effective control, but increased injury potential at 0.4 cm compared to 4.0 cm mowing height.