Amicarbazone and methiozolin are herbicides with efficacy for annual bluegrass (Poa annua L.) control in creeping bentgrass (Agrostis stolonifera L.). Greenhouse research was conducted at the University of Tennessee (Knoxville, TN) to determine the effects of rooting depth and soil type on creeping bentgrass injury with amicarbazone and methiozolin. The effects of soil texture on annual bluegrass control efficacy were evaluated in field studies conducted on golf greens in Knoxville, TN and Lubbock, TX.

 

‘Penncross’ creeping bentgrass was established in sand- or soil-based rootzones using mini-rhizotrons in the greenhouse. Plants were treated with amicarbazone (49, 98, 196 g ha^-1) or methiozolin (500, 1000, 2000 g ha^-1) once root growth reached depths of 5, 10, and 15 cm. Amicarbazone was more injurious than methiozolin in both rootzones. Creeping bentgrass injury with amicarbazone measured 62% in soil compared to only 38% in sand. In addition 54 to 69% reductions in root length density were observed in the sand-based compared to 42 to 81% reductions in soil. Methiozolin resulted in ≤ 12% creeping bentgrass injury, regardless of rootzone type or application rate, and reduced root length density ≤ 25%. Amicarbazone injury was lower at the 15 cm rooting depth compared to the 5 and 10 cm rooting depths. Responses indicate that methiozolin is less injurious to creeping bentgrass than amicarbazone and that rooting depth and soil type affect creeping bentgrass injury with amicarbazone.

 

Field experiments evaluated annual bluegrass control efficacy with methiozolin using two application rates (500 and 1000 g ha^-1) and six application regimes [October, November, December, October followed by (fb) November, November fb December, and October fb November fb December] on sand- and soil-based putting greens. Annual bluegrass control with methiozolin at 1000 g ha^-1 on sand-based greens ranged from 70 to 72% compared to 87 to 89% on soil-based greens. Treatment at 500 g ha^-1 controlled annual bluegrass 57 to 64% on sand-based greens compared to 72 to 80% on soil-based greens. Sequential application programs controlled annual bluegrass 70 to 79% on sand-based greens and 85 to 92% on soil-based greens. Responses indicate that soil type and rooting depth affect the activity of amicarbazone and methiozolin applications for weed control on creeping bentgrass putting greens.