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Turf managers are demanding alternate fertilization strategies for golf course fairways, including those that provide efficent nutrient use, controlled nitrogen (N) release, and take advantage of elicitor (phosphite-H₃PO₃) technology.   These programs are specifically designed to maximize turf vigor during the summer and at the hieght of environmenal stress.  High N rates are routinely supplied in the spring and fall to cool season turfgrasses, when the capacity for shoot and root growth is highest.  In order to maintain optimum creeping bentgrass (CB) quality and vigor in the summer, a bulk granular fertilizer application using slow release N with low burn potential is often implemented.  Previous research has documented the benefit of soluble N appliations to reduce dollar spot (Sclerotinia homeocarpa) incidence, and also the use of potassium phosphite (K₂HPO₃) to increase plant health and manage Pythium blight (Pythium spp.).   The objectives of this research trial was to 1.) Determine the effect of N rate/source and phosphite on CB quality 2.)  Determine the effect of N rate/source and phosphite on dollar spot and pythuim blight incidence. Treatments included split granular N applications at annual rates of 1, 2, and 3 lbs N/M/Yr from ammonium sulfate [(NH₄)₂SO₄] (21-0-0).  One application was made in the spring (15 May), the other in the fall (1 Oct).  Combined granular and foliar fertilization treatments included split applications of granular 21-0-0 in the spring and fall (0.84 lbs N/M per application) plus Burley Green (BG) (18-2-3; 50% slow release N) + Amino Iron (AI) (12-0-0; 5Fe) and +/- Fairphyte (FP) (1-0-26; 26% phosphite-K₂HPO₃) applied every three (3) weeks (0.08 lbs N/M/application) during the summer for a total N input of 2 lbs N/M/Yr.  No pythium blight was reported during the course of this study.  As expected, higher N rates corresponded to higher CB quality (Figure 1).  BG + AI treatments provided better turf quality than each applied alone at the same N rate (0.08 lbs N/M) (data not shown).  Combined foliar (BG + AI) and granular treatments, which supplied 2 lbs N/M/Yr, provided equal turf quality during the summer as the granular only treatment which supplied 3 lbs N/M/Yr, and significantly better turf quality than granular only treatments supplying an equivalent amount of N (2 lbs/M/Yr) (Figure 1).   The addition of phosphite did not effect the overall quaility of CB, however only the combined granular and foliar fertilizer treatments (+/- phosphite) provided commercially acceptible turfgrass quality throughout the duration of the study.  Higher N rates corresponded to lower dollar spot incidence regardless of N source, and a trend occurred whereby phosphite treatments lessened the incidence and severity of dollar spot (Figures 2&3).  The only treatments that provided consistent and significanly better dollar spot suppression during the summer than the untreated control included the highest granular only N rate (1.5 lbs N) and the combined granular +  foliar fertilizer (BG+AI) + phosphite (FP) treatment (0.94 lbs N/M on 29 Jun; 1.02 lbs/N on 9 Jul) (Figure 2).  The results suggest that a combined granular (spring and fall) and foliar (summer) fertilization strategy will maximize nitrogen (N) use efficiency and CB quality.  The foliar approach to summer fertilization maximizes CB color and quality by providing controlled and long lasting (3-4 weeks) N release, and by supplying a compatible and balanced nutritional package including  phosphorus (P), potassium (K), iron (Fe), manganese (Mn), and zinc (Zn).  Potassium phosphite provided some level of dollar spot suppression, however this appears to be the the first report to date of this observation.

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