Brown patch severity as affected by cool-season turfgrass species, cultivar, and nitrogen rate

Brown patch (caused by various Rhizoctonia and Rhizoctonia-like species) is a major summer disease for several cool-season turfgrass species, including creeping bentgrass (CBG) (Agrostis stolonifera L.), colonial bentgrass (CLBG) (Agrostis capillaris L.), perennial ryegrass (PRG) (Lolium perenne L.), and turf-type tall fescue (TTTF; [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.]). Elevated nitrogen (N) rates are suggested to enhance development of brown patch symptoms. A controlled environment study was conducted to determine the influence of two N rates among four cool-season turfgrass species maintained at 1.9 cm after inoculation with R. solani. Field-grown plants of four CBG cultivars, a CLBG cultivar, a PRG blend, and two TTTF cultivars were fertilized weekly, totaling 49 and 196 kg N ha-1 across four applications. Turfgrass responses were measured as relative growth rate, brown patch severity, and seasonal brown patch using area under the disease progress curve (AUDPC). On average, peak brown patch severity among the species and cultivars was between 22.6% and 68.1% for Raptor III TTTF and Penn A-1 CBG, respectively. Turf-type tall fescue cultivars decreased brown patch by 61% compared to CBG, CLBG, and PRG. The lower N rate reduced brown patch AUDPC by 17% and 33% for CBG and PRG, respectively, but N rate generally had no effect for CLBG and TTTF. These results reinforce the importance of planting disease-resistant species and cultivars. Additionally, N rate may be an important factor affecting brown patch severity for select intensively managed turfgrass species. Among the four cool-season turfgrass species studied, tall fescue was the most resistant to brown patch. Brown patch-resistant cultivars had significantly less disease compared to susceptible cultivars. Increased nitrogen rates were associated with enhanced brown patch in creeping bentgrass and perennial ryegrass. Nitrogen rate did not influence brown patch severity on the colonial bentgrass and tall fescue.