Late Season N and Plant Growth Regulator (PGR) Applications Influence Spring Vigor of Cool-Season Putting Greens.

Winter injuries of creeping bentgrass (Agrostis stolonifera L.)/annual bluegrass (Poa annua L.) cohabited golf course putting greens (PG) are common across the Northern United States and Canada. A field experiment was initiated in Sept. 2009 to determine optimal timing of late season N applications, as well as the interactive and/or main effects of N and plant growth regulator treatments on winter survival and spring vigor of an intensively-managed PG within the Pennsylvania State Univ. Valentine Turfgrass Research Center (University Park, PA). The experimental design comprised paired main plots of pentachloronitrobenzene (PCNB) treatment or none, each containing treatments of N (30 or 60 kg ha-1), trinexapac-ethyl (TE; 0, 0.088, or 0.044 + 0.044 kg ha-1), and four Fall application timings; in a completely-randomized, 24-split-plot arrangement. Resulting turfgrass clipping yield (CY; kg ha-1), tissue N (g kg-1), canopy density (green normalized differential vegetative index; GNDVI), and snow mold incidence (% area) were measured in March and early-April of 2010. Preventative PCNB treatment significantly suppressed snow mold incidence while enhancing Spring CY and GNDVI. Spring CY decreased linearly over early to late-Fall application dates, but Spring GNDVI showed a cubic response to fall timing. While Spring CY and GNDVI were directly related to Fall N rate, no significant interactions among the N and TE treatments were observed. Throughout each N level applied on any Fall date, Spring CY was significantly curtailed by the split-rate of TE (compared to the zero or full rate). Yet TE, applied at either the split or full rate, resulted in significantly-increased Spring GNDVI compared to untreated plots. In summary, Spring PG density and vigor appear positively influenced by Fall inputs of N & TE, particularly when applied up to 15-d prior to the first hard frost.