Response of Two Annual Bluegrass Varieties to Preemergence and Postemergence Rimsulfuron1

Abstract

In greenhouse studies, flowering annual bluegrass Poa annua L. var. annua (winter annual) and P. annua L. var. reptans (short-lived perennial) were treated postemergence with rimsulfuron at 54 g ai/ha in such a manner as to permit herbicide interception only by the foliage, interception only by the soil, and interception by both foliage and soil, as would occur in a typical application. The foliar-only, soil-only, and soil foliar applications provided 57, 73, and 84% control, respectively, as averaged over all other experimental variables. Greater efficacy of the soil-only and soil foliar applications indicated the importance of root absorption for annual bluegrass control with rimsulfuron. Adjuvant addition was beneficial to postemergence activity only at 18 g/ha, which is below the registered rate. Adjuvant-based control improvement at this rate was inconsistent and generally independent of the adjuvant type. Adding Renex-30 to 18 g/ha of rimsulfuron did increase control on an average from 16 to 51%. Postemergence efficacy was also independent of the annual bluegrass variety and growth media (field soil vs. a sand–peat mixture). Preemergence activity of rimsulfuron against germinating annual bluegrass seeds was slightly greater in the sand–peat mixture than in the soil and with var. annua than with var. reptans, and on uncovered seed compared with 0.5-cm-deep growth media covered seeds.Nomenclature: Rimsulfuron; annual bluegrass, Poa annua #3 POANN.Additional index words: Adjuvant study, herbicide absorption by plants, herbicide placement, surfactant study, turfgrass weeds.Abbreviations: WAT, weeks after treatment.