Effects of nitrogen, phosphorus and potassium rates on Microdochium patch

Research on nitrogen (N), phosphorus (P) and potassium (K) ratios have suggested that maintaining the proper balance of those nutrients is critical to disease mitigation. However, research on N, P, and K ratios relevant to annual bluegrass ( Poa annua L.) and Microdochium patch ( Microdochium nivale ) is not available. The objective of this research was to evaluate the effects of winter‐applied N, P, and K rates in combination with sulfur and phosphorous acid on Microdochium patch development within an annual bluegrass putting green in the absence of traditional fungicides. Field research was conducted from October 2018 to April 2019 on a mature sand‐based annual bluegrass putting green. Factors included monthly applications of urea nitrogen (46–0–0) rate (4.9 kg N ha –1 and 9.8 kg N ha –1 ), phosphorus rate (0.0 kg P ha –1 and 1.22 kg P ha –1 ), and potassium rate (0.0 kg K ha –1 and 4.9 kg N ha –1 ). To avoid extreme disease levels, all of these treatments received monthly applications of phosphorous acid. When comparing nitrogen treatments across both rates vs. nitrogen combined with P, K or both, disease levels decreased from 9.9 percent (urea only) to 5.5 percent (urea with P, K, or both). Additionally, when nitrogen rates increased from 4.9 kg N ha –1 to 9.8 kg N ha –1 , the percent disease decreased from 8.4 to 4.8 percent. Findings from this project suggest that applying nitrogen only as urea will lead to more Microdochium patch vs. applying urea with P, K, or both, and nitrogen applied at the higher rate will decrease Microdochium patch incidence.