Methiozolin Effects on Annual Bluegrass Control at Various Seasonal Timings and Creeping Bentgrass Injury in Shade

Abstract

Methiozolin is a new herbicide with efficacy against annual bluegrass (Poa annua L.; ABG) and is being investigated as a selective herbicide in creeping bentgrass (Agrostis stolonifera L.; CBG) golf course greens, tees and fairways. However, the ideal seasonal timing for methiozolin remains unclear, wide ranges of ABG control have been reported and not all seasonal timings have been tested. Additionally, golf course superintendents often manage shaded tees and fairways, yet the influence of methiozolin on CBG grown in reduced light is unknown. Field studies were conducted from 2015-2017 in New Jersey on mixed CBG and ABG soil-based putting greens to investigate a wide range of spring and fall timings of methiozolin. Sequential applications totaling 1.44 kg ai ha-1 controlled ABG 72% to 87% (study 1) and 77% to 93% (study 2) at 12 WAIT and best control resulted from Sep 1 and Oct 1 seasonal timings. CBG injury remained at acceptable levels throughout both studies at all seasonal timings. Oct 1 (Study 2) and Nov 1 seasonal timings reduced total green cover up to 20% and voids in coverage persisted until the following spring. Greenhouse experiments (repeated in time) were conducted in New Jersey testing sequential methiozolin applications totaling 2.88 kg ai ha-1 on 6 cultivars of CBG maintained at fairway height in 3 shade treatments. Methiozolin reduced CBG clipping dry weights ≤ 50% at 21 and 42 DAIT among all cultivars in 40% shade. The cultivars Princeville and 007 were significantly less tolerant to methiozolin in all shade treatments. Results suggest that methiozolin Sep 1 seasonal timing is optimal for achieving ABG control while providing good CBG safety, late fall timings should be avoided and moderate (40%) shade reduces CBG vigor enhancing injury following applications of methiozolin.