Fungicide soil application efficiency for the control of black scurf (Rhizoctonia solani) on three potato cultivars

Abstract: In the 2004 and 2005 seasons, experiments were carried out at INTA Balcarce, Argentina on potato cultivars Kennebec, Innovator and Shepody, with different susceptibility to Rhizoctonia solani Kuehn. A randomized block design with four replications was created. Visual observations during the crop cycle were carried out in order to record the number of healthy and infected plants, with symptomatology of stem canker produced by R. solani. After harvest, the potatoes in each block were washed and weighted, the total yield recorded and the marketable and "seed" potatoes were classified into healthy, cracked or malformed tubers. The best results on the reduction of infected plants were obtained with the highest dose of fluazinam (as Frowncide 50SC) and pencycuron (as Monceren 25SC). Commercial and "seed" tuber yields in the Spunta cultivar showed no significant differences among treatments, but with the Shepody cultivar, when the severity of the disease was high (2004) both fungicide treatments surpassed the untreated check. When the severity of the disease was low (2005), all chemical treatments registered higher commercial and "seed" tubers yields than the untreated check. In Kennebec and Spunta cultivars, all the treatments - except the lowest dose of fluazinam - accomplished a higher quantity of healthy tubers and surpassed the untreated check; although only the highest doses showed the highest yield of healthy tubers, showing a positive relationship with respect to the applied dose. Only the highest doses of fluazinam considerably reduced diseased tuber incidence in comparison to the untreated check.