A study on the relationship between the climatic conditions during the year, and the development of the South American leaf blight of the rubber tree, on the São Paulo State plateau was made. Several phenological observations on the pathogen and its host were made for this purpose, in different regions of the State. The results obtained were correlated with meteorological elements and local topoclima. Phenological ages of the foliar flows were defined accordingly to the system proposed by Thornthwaite & Matter, and Higgins. Data collected mainly in Pindamonhangaba county, showed that mild infections occurred from January to May, when the climatic conditions are more favorable to the pathogen,, affecting only 2 or 3 of the foliar shoots, among the 5 or 6, which normally appear each year. In Campinas a similar pattern was observed. In Ribeirão Prêto county, as well as in higher lands with good drainage of the cold air, no infection was observed. It was concluded that under the climatic conditions of São Paulo State plateau, and similar areas in neighboring States, the culture of rubber tree would be feasible, even using clones susceptible to the leaf blight.