Creeping Bentgrass Water Use in Response to Plant Growth Regulators and Evapotranspiration Replacement.

Golf course managers are seeking ways to reduce maintenance inputs like supplemental irrigation. Fairways represent the largest acreage of intensively managed turf, with water often applied for aesthetics rather than plant health or playability. Studies were conducted on creeping bentgrass (Agrostis stolonifera L.:CBG) to measure water use under deficit irrigation and determine if plant growth regulators (PGRs) could reduce water needs. In a greenhouse study, CBG was grown in a 30-cm deep sand/porous ceramic media and maintained at 12 mm; water use, visual quality and green turf cover were measured for CBG subjected to deficit irrigation based on evapotranspiration (ET) rates of 40, 60 and 80% with or without two preformulated PGR products: flurprimidol (FL)+trinexapac-ethyl (TE) or FL+TE+paclobutrazol (PB). Water use was measured for 77 and 109 days with daily use rates ranging from ~4.0 to 4.7 mm for non-PGR treatments, ~3.8 to 4.3 mm for those treated with FL+TE, and ~3.8 to 4.2 mm for those treated with FL+TE+PB. Turf treated with FL+TE+PB across all ET replacement rates had higher quality compared to the untreated and those treated with only FL+TE. Green cover was greatest in the 40 and 60% replacement rates for FL+TE+PB, while FL+TE slightly outperformed the FL+TE+PB treatment at 80% ET. FL+TE+PB at 60% ET replacement maintained highest quality and green cover at the lowest water use rate. Select greenhouse treatments were repeated in the field on a silt-loam soil at supplemental irrigation amounts of 80, 65, and 50% ET with and without PGRs. Visual appearance was greatest for the 80% ET replacement, but quality decreased only slightly at the 65 and 50% ET replacement rates with and without PGR treatments. These studies demonstrate that supplemental irrigation needs for fairway CBG could be substantially reduced with a combination of deficit irrigation and PGRs.