Nitrogen Rate and Growth Regulator Effects On Shaded Velvet and Creeping Bentgrasses.

Shading of golf course putting greens often reduces turf quality and performance.  Anecdotal claims suggest that velvet bentgrass (Agrostis canina L., VBG) is more shade tolerant than creeping bentgrass (A. stolonifera L., CBG).  Our objective was to compare the shade tolerance of VBG to CBG putting green turf under 80% shade.  The experimental design was a randomized block, strip-split plot with four replications.  ‘Vesper’ VBG and ‘Tyee’ CBG were planted on a Plano silt loam (pH 7.3) in July 2008.  Foliar urea N was applied as a strip-plot treatment every 14 d at annual N rates of 49, 98, and 196 kg ha^-1.  Trinexapac-ethyl (TE, 0.05 kg a.i. ha^-1) was applied as a split-plot treatment every 28 d. Treatments were applied May through October in 2009 and 2010.  Shade cloth was erected commensurate with tree leaf development in May of both years and was removed at fall leaf drop.  Turf quality, clipping yield, and ball roll data were collected during the May to October growing season.  Fertilizer rate affected quality more than TE application, though both were significant. Bentgrass species did not affect turf quality in 2009.  No treatment provided acceptable turf quality for the entire growing season. Velvet bentgrass had less clipping yield than CBG.  Nitrogen rate and bentgrass species affected ball roll but not at distances detectable by golfers.  First year data showed that VBG and CBG had similar quality under shaded conditions.  The application of TE and 98 kg ha^-1 N resulted in the highest quality turf for the longest duration.