Annual bluegrass is a problematic turfgrass weed. Methiozolin is a new, currently unregistered herbicide that selectively controls annual bluegrass in desirable turfgrasses. Studies were conducted to evaluate and compare annual bluegrass control from PRE-applied methiozolin as influenced by rate and soil type and from POST-applied methiozolin as influenced by rate, soil type, annual bluegrass growth stage, and treatment placement. Studies were also conducted to evaluate foliar and root absorption and subsequent translocation of methiozolin by annual bluegrass using radio-tracer techniques. PRE-applied methiozolin controlled annual bluegrass > 99%. POST-applied methiozolin resulted in < 80% control regardless of foliar versus root exposure. POST applications are more effective at higher rates and smaller growth stages. Foliar-plus-soil methiozolin application trended to result in the best control, compared to foliar-only and soil-only applications. Absorption and translocation data indicate that methiozolin is absorbed by both leaves and roots and moderately translocates upward in the plant toward the leaf tip with little to no basipetal translocation. Because control is limited from a single methiozolin application (as observed in POST experiments), successful field application of methiozolin requires multiple and timely applications directed toward the roots and/or foliage of annual bluegrass.

Nomenclature: Methiozolin, MRC-01, 5-(2,6-difluoro-benzyloxymethyl)-5-methyl-3-(3-methyl-thiophen-2-yl)-4,5-dihydro-isoxazole; annual bluegrass, Poa annua L.