Control of potato late blight and early blight by fungicides and its effects on yield and quality of tubers

ABSTRACT: Late blight (Phytophthora infestans) and early blight (Alternaria solani) are among the most current and destructive diseases of potato. With the aim of evaluating the efficiency of different fungicides in the control of both diseases, two experiments were carried out in commercial potato crops (cultivars Agata and Monalisa) in Pilar do Sul, São Paulo State, Brazil, during 2008 and 2009 cropping season. Randomized block designs were used, with 4 replications and each parcel of 20 m2. Applications were carried out using coastal sprayer with spray-bar under constant pressure of 3 Bar. The application volume varied from 300 to 500 L per hectare according to the crop development. The evaluated variables for both diseases were: severity on leaves, area under disease progress curve (AUDPC), total and commercial yield, and classification of tubers. For late blight, the lower severity levels and significant increases in commercial yield and quality tubers were observed on the rows treated with fluopicolide + propamocarb, dimetomorph + ametoctradin, mandipropamid + chlorothalonil, mandipropamid, fenamidone + propamocarb, benthiavalicarb + fluazinam, followed by dimetomorph + chlorothalonil, mefenoxam + chlorothalonil e famoxadone + cymoxanil + mancozeb and, for early blight, azoxystrobin + difenoconazole, picoxystrobin, pyraclostrobin +metconazole, trifloxystrobin + tebuconazole, azoxystrobin, boscalid + pyraclostrobin, iprodione + pyrimethanil and cyprodinil.