In Vitro Fungicide Sensitivity of Rhizoctonia and Waitea Isolates Collected from Turfgrasses

Different Rhizoctonia species and anastomosis groups (AGs) have been reported to show variable sensitivity to commercial fungicides. Thirty-six isolates of Rhizoctonia collected from turfgrasses were tested in vitro for sensitivity to commercial formulations of iprodione, triticonazole, and pyraclostrobin. Tested isolates represented R. solani AG 1-IB and AG 2-2IIIB; W. circinata varieties zeae (Wcz) and circinata (Wcc); and binucleate Rhizoctonia-like fungi (BNR) from different locations in Virginia and Maryland. Each fungicide was added to PDA medium to obtain concentrations at 0, 0.1, 1, 10 and 100 mg a.i.·L−1 (0.00001, 0.0001, 0.001 and 0.01 oz a.i.·gal−1). A mycelium plug from each isolate was grown on these plates. The fungicide concentration needed for 50% inhibition of radial growth (EC50) was determined for each isolate by fungicide combination. Waitea circinata isolates were moderately sensitive (EC50 = 1 to 10 mg a.i.·L−1) (0.0001 to 0.001 oz a.i.·gal−1) to iprodione while isolates of R. solani...