Long-Term Roughstalk Bluegrass Control in Creeping Bentgrass Fairways

Methiozolin is an isoxazoline herbicide that selectively controls annual bluegrass in cool-season turf and may control roughstalk bluegrass, another weedy Poa species that is problematic in many turfgrass systems. However, the majority of research to date is limited to evaluating methiozolin efficacy for annual bluegrass control in creeping bentgrass putting greens. Research was conducted comparing various application regimes of methiozolin and other herbicides for long-term roughstalk bluegrass control in creeping bentgrass golf fairways. Methiozolin-only treatments did not injure creeping bentgrass or reduce normalized difference vegetative index (NDVI) at 2 golf course locations based on 20 evaluation dates over a 2.5-yr period. The 2.5-yr average turf quality generally declined as roughstalk bluegrass control increased due to transient turf cover loss. At 1 yr after last treatment, methiozolin at 1500 g ai ha⁻¹ applied four times in fall reduced roughstalk bluegrass cover 85%. This was equivalent to methiozolin at 1000 g ha⁻¹ applied four times in fall, but greater than low rates of methiozolin applied four times in spring or twice in fall and spring. Amicarbazone, primisulfuron, and bispyribac-sodium alone either did not effectively reduce roughstalk bluegrass cover, or did so at the expense of increased creeping bentgrass injury. Results of this study suggest that methiozolin alone or tank-mixed with amicarbazone or primisulfuron is an effective long-term approach for selectively controlling roughstalk bluegrass in creeping bentgrass. Nomenclature: Amicarbazone; bispyribac-sodium; methiozolin; 5-(2,6-difluorobenzyl)oxymethyl-5-methyl-3-(3-methylthiophen-2-yl)-1; 2-isoxazoline; code names: EK-5229, SJK-03, and MRC-01, prmisulfuron, annual bluegrass, Poa annua L.; roughstalk bluegrass, Poa trivialis L.; creeping bentgrass, Agrostis stolonifera L.