Evaluation of calcium silicate for brown patch and dollar spot suppression on turfgrasses

Nonfungicide alternatives for control of brown patch (caused by Rhizoctonia solani Kuhn) and dollar spot (caused by Sclerotinia homoeocarpa F.T. Bennett) diseases are needed. Calcium silicate (CaSiO 3 ) was applied as a topdressing (2440 or 4880 kg ha -1 ) to evaluate brown patch suppression in 'Bonsai 2000' and 'Tar Heel' tall fescue (Festuca arundinacea Schreb.) and 'L-93' creeping bentgrass (Agrostis palustris Huds.) in the field, or amended into soil at 7325 or 14650 kg ha -1 to evaluate dollar spot on 'Penncross' creeping bentgrass in a growth chamber. The Chase silty clay loam (fine, mont-morillonitic, mesic Aquic Argiudoll) under tall fescue had a pH of 6.4, a high initial Si content (173 mg kg -1 ), and Si accumulation in leaves was minimal (one of five observations). Calcium silicate applied at 2440 kg ha -1 increased the area under disease progress curves (AUDPC) for brown patch by 26% in 2002 and 30% (both rates) in 2003. Tall fescue leaf P and K concentrations were reduced by CaSiO 3 and were negatively correlated (r = -0.41 for P; -0.44 for K; P < 0.02) with brown patch. Calcium silicate topdressing increased Si in creeping bentgrass leaf tissue as well as the sand root zone, which initially contained <12 mg kg Si. A positive correlation (r = 0.81; P < 0.001) occurred between creeping bentgrass leaf Si concentration and brown patch severity in one of three years, which may have resulted from reduced leaf P and K after CaSiO 3 application. The silty clay loam (170 mg kg -1 Si) amended with CaSiO 3 before planting creeping bentgrass had no effect on leaf Si concentrations or dollar spot incidence. Thus, CaSiO 3 application to soil containing adequate Si should not be recommended for control of brown patch on tall fescue, nor should CaSiO 3 be recommended to control brown patch on creeping bentgrass grown on low Si soil or dollar spot on high Si soil. In fact, CaSiO 3 application may exacerbate brown patch disease incidence possibly because of nutrient imbalances, particularly in tall fescue.