SELECTIVITY OF METHIOZOLIN FOR ANNUAL BLUEGRASS CONTROL IN CREEPING BENTGRASS GOLF GREENS AS INFLUENCED BY TEMPERATURE AND APPLICATION TIMING.  P. McCullough; Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223; D. Gómez de Barreda, Polytechnic University of Valencia, Spain; J. Yu, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223.

ABSTRACT

Methiozolin controls annual bluegrass in creeping bentgrass but application timing and temperature could influence efficacy in turf.  In field experiments, sequential methiozolin applications totaling 3.36 kg ai ha^-1 provided excellent (>90%) annual bluegrass control at 8 weeks after initial treatment when treatments were initiated in Feb./March or May but programs totaling 0.84 and 1.68 kg ha^-1 provided poor control (<70%) at both timings.  Methiozolin at all rates caused minimal turf injury (<8%) but creeping bentgrass was only injured from Feb./March applications.  In growth chamber experiments, creeping bentgrass injury from methiozolin at 10 C was 2 and 4x greater than at 20 C and 30 C, respectively, while annual bluegrass injury was similar across temperatures.  In laboratory experiments, annual bluegrass had more foliar absorption of ¹⁴C-methiozolin than creeping bentgrass at 30/25 C (day/night), compared to 15/10 C, but translocation was similar at both temperatures as >90% of absorbed ¹⁴C remained in the treated leaf after 72 hours.  Annual bluegrass distributed and recovered more radioactivity to shoots from root-applied ¹⁴C-methiozolin than creeping bentgrass while both species had about 2x more distribution to shoots at 30/25 C than 15/10 C.  Metabolites were not detected in annual bluegrass or creeping bentgrass at 1, 3, or 7 days after treatment when grown at 15/10 C or 30/25 C suggesting uptake and translocation contributes to methiozolin selectivity in turfgrass.