Prohexadione-Calcium Efficacy for Annual Bluegrass Suppression, Seedhead Control, and Clipping Management.

Plant growth regulators (PGRs) are widely used to reduce mowing requirements and enhance turfgrass quality.  The objective of these experiments was to investigate efficacy of a new PGR, prohexadione-calcium, for clipping management, seedhead inhibition, and annual bluegrass suppression.  Over three years in New Jersey, monthly prohexadione-calcium applications from 0.28 to 0.56 kg ai/ha reduced creeping bentgrass and perennial ryegrass fairway clippings similar to trinexapac-ethyl by approximately 20 to 60% from the untreated for two to three weeks after applications.  Prohexadione-calcium applications frequently enhanced creeping bentgrass and perennial ryegrass color and quality by approximately 10 to 15% from the untreated.  Biweekly prohexadione-calcium applications from 0.1 to 0.14 kg ai/ha to a creeping bentgrass putting green reduced clippings and enhanced turf quality similar to trinexapac-ethyl at 0.05 kg ai/ha from May to September.  In two experiments, prohexadione-calcium temporarily suppressed annual bluegrass in creeping bentgrass and perennial ryegrass fairways but suppression was not detected in the following year and results were less consistent than paclobutrazol treatments.  Spring applications of prohexadione-calcium from 0.14 to 0.56 kg ai/ha suppressed annual bluegrass seedheads similar or better than mefluidide and ethephon plus trinexapac-ethyl but injury, ranging 20 to 57%, was more substantial than other PGRs.