In Vitro Evaluation of Selected Fungicides Against Rhizoctonia solani Causing Black Scurf of Potato

Black scurf, caused by Rhizoctonia solani Kühn, is an important soil-borne disease of potato that adversely affects crop establishment, plant growth, tuber quality and yield. The pathogen persists in soil and infected planting material, making its effective management challenging. The present study was conducted to assess the inhibitory activity of selected fungicides against R. solani under laboratory conditions using the poisoned fo od technique. Ten fungicidal treatments were evaluated at concentrations of 10 and 15 ppm in a Completely Randomized Design with three replications. Radial mycelial growth of the pathogen was recorded and the percentage inhibition relative to the untreated control was calculated. Marked differences were observed among the fungicides in their ability to suppress mycelial development at both concentrations. Sedaxane 70% + Fludioxonil 4.63% FS showed complete inhibition of R. solani, recording 100% inhibition at both 10 and 15 ppm. At 10 ppm, Azoxystrobin 23% SC, Thifluzamide 24% SC, Penflufen 22.43% FS and Carboxin 37.5% + Thiram 37.5% produced 87.78, 85.56, 83.33 and 80.85% inhibition, respectively. At 15 ppm, Azoxystrobin 23% SC resulted in 90.00% inhibition, followed by Thifluzamide 24% SC (89.26%), Penflufen 22.43% FS (88.15%) and Carboxin 37.5% + Thiram 37.5% (88.15%). Carbendazim 25% WP + Mancozeb 50% WP exhibited the lowest inhibitory effect, with 12.04% inhibition at 10 ppm and 34.26% at 15 ppm. Overall, Sedaxane + Fludioxonil, Azoxystrobin and Thifluzamide demonstrated strong in vitro activity against R. solani and may warrant further evaluation under field conditions.