The postemergence herbicide ethofumesate and the plant growth regulator paclobutrazol were evaluated for annual bluegrass control in creeping bentgrass turf managed as golf fairways. Both products were applied under several different timing regimes relative to the time of the year. Paclobutrazol treatments provided significantly greater annual bluegrass control than ethofumesate. There were no differences between rates of paclobutrazol (0.28 and 0.14 kg ai/ha) when applied from spring through summer. Annual bluegrass control after spring and summer applications of paclobutrazol was 85% or more. Clipping weight data indicated that paclobutrazol suppressed growth in annual bluegrass longer than in creeping bentgrass. It was concluded that prolonged suppression of annual bluegrass by paclobutrazol resulted in creeping bentgrass dominance and subsequent annual bluegrass control. Additionally, applications of ethofumesate in autumn–winter, followed by paclobutrazol applied in spring–summer, provided significant control of annual bluegrass in 1 yr of the study.
Nomenclature: Ethofumesate; paclobutrazol, (±)-(R*R*)-β-([4-chlorophenyl]-methyl)-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol; annual bluegrass, Poa annua spp. annua L., spp. reptans Hausskn. #3 POAAN; creeping bentgrass Agrostis stolonifera L. ‘Penncross’, ‘Providence’.
Additional index words: Growth suppression.
Abbreviations: AUPPC, area under percent Poa curves; DAA, days after application; GA, gibberellic acid.