The marketing of potato is heavily hindered by the presence of physiological defects of the tubers. In order to verify the influence of planting time on the occurrence of such defects and its relation with the type of soil and varieties as well, a series of observations was made in different experimental feilds all over the state of São Paulo. It was concluded that the brown spot, followed by second tubers, caused the most harmful defects to the tubers during the rainy season, since the intense changes of temperature and humidity during this period of time favor the occurrence of such diseases, which does not usually happen during the dry season. Further, an entirely different behavior was observed with varieties with regard to black heart and hollow heart, as these have no economic importance occurring with no intensity. The sandy soils with a low power of water retention showed the most intense occurrence of the defects.