| Rhizoctonia species are important pathogens to turfgrasses, yet little is known about the structure of populations or the effect of disease control programs on population dynamics. Isolates of Rhizoctonia were obtained from a creeping bentgrass putting green in 2002 and 2003 and from tall fescue landscapes in 2003. Creeping bentgrass isolates were obtained by placing 5 mm soil cores on alkaline water agar, incubated at ∼24 C for 48 hrs and the actively growing hyphae were transferred to PDA. Tall fescue isolates were obtained from foliar lesions using the same procedures. Isolates were characterized using morphological characteristics, anastomosis reactions, nuclear staining, and ribosomal DNA sequences. From creeping bentgrass, 21 distinct clones of R. solani AG 2-2 IIIB were present in the sample population in 2002. Seven of these clones were recovered on multiple sampling dates. Fifteen of the 21 clones from 2002 were recovered in 2003. All seven clones that were isolated in multiple sampling dates in 2002 were recovered in 2003. All 21 clones exhibited similar EC50 values to mancozeb, chlorothanlonil and azoxystrobin. Of 224 isolates collected from tall fescue during 2003, 88 were R. solani AG 1, 105 were binucleate Rhizoctonia CAG 1, 14 were R. zeae, two were R. cerealis, and 15 were not identified. One hundred and seventy four of the isolates were assayed for sensitivity to the fungicides flutalonil, iprodione, tebuconazole, and trifloxystrobin. Mean EC50 values varied across fungicides and species, but were below 3.3 mug ml -1. The diversity of Rhizoctonia populations associated with tall fescue, and the range in fungicide sensitivities among species indicates that response to management programs may vary with location and environment. The effects of phosphorous acid on fungal growth, disease incidence and turfgrass quality was evaluated. Mean EC50 values of azoxystrobin for R. solani 2-2 IIIB, and AG 1, P. aphanidermatum, and R. zeae were 1.27, 0.04, 0.012, and 0.145 mg L-1, respectively. Applications of phosphorous acid to creeping bentgrass and tall fescue did not reduce brown patch or increase turfgrass quality. The benefit of phosphorous acid as a fungicide or plant nutrient is questionable. |
