Safety of Sequential Fall Methiozolin Applications on Creeping Bentgrass Putting Greens

Abstract

Methiozolin is an herbicide with preemergence (PRE) and postemergence (POST) activities for control of annual bluegrass (AB; Poa annua L.). Previous research reported that fall applications provide better control than spring applications when methiozolin is applied as a POST, and PRE application appears to show a higher degree of efficacy than POST applications. Preemergence application for AB control on creeping bentgrass (CB; Agrostis stolonifera L.) putting greens requires treatment starting in late summer to early fall, when CB greens are likely under summer stress. Three field studies were conducted to evaluate the safety of fall sequential methiozolin applications on CB greens. Treatments consisted of methiozolin at 0.22, 0.45, 0.67, or 0.89 lb a.i./acre applied 1, 2, or 4 weeks apart, totaling 1.78 to 2.01 lb a.i./acre per season. Phytotoxicity was consistently observed in one out of three studies but was at an acceptable level (≥6 on a scale of 1–9) in all evaluations. Methiozolin applications, regardless of rate or application interval, resulted in a consistent AB control up to 95% over the season, compared with the nontreated control. Results suggest that sequential applications of methiozolin in fall with the initial treatment starting in late summer to early fall may provide effective AB control with acceptable safety to CB putting greens.