Phytophthora infestans Mont. de Bary, causes one of the most important diseases in potato fSolanum tuberosum L.). Since the last decade, repeated years of 'blight' affecting many varieties and cultivars have been observed in Chile. This has led to the validation of different early warning systems, the Blitecast model being one of the most efficient. The aim of this study was to assess the response of native varieties and com mercial cultivars of potato to natural infections of late blight, managed on the basis of early warning system. During the 2006/2007 season, a study was conducted with a split plot de sign with four replications and factorial arrangement of treat ments, with seven genotypes and two early warning systems as study factors. Native varieties used were Michuñe azul and Clavela and cultivars Desirée, Yagana, Karu, Pukará and Car dinal. The early warning systems assessed were the Blitecast model and a witness without chemicals, as a decision tool to apply chemical control. No interaction effects were observed in the study (p>0.05). The leaf damage and area under the curve of disease progress (AUDPC) were significantly lower (p<0.05) in cv. Cardinal than cv. Desirée, in coincidence with the offi cial description of both cultivars. The AUDPC ranked Michuñe azul (119.39) and Clavela (120.54) as moderately resistant vari eties. The main effects of an early warning system reduced sig nificantly (p<0.0001) the AUDPC and leaf damage of the crop. The latter was reduced by 64.5% when compared with the system without early warning.