Correlations were determined between the average incidence of P. striiformis, P. recondita and P. graminis on several hundred wheat lines, under study each year, with rainfall and sum of degree-days (base 5º C), o different periods in the respective years. There were no correlations between degree-days and the incidence of P. striiformis and P. recondita, in any of the periods considered. A high correlation was found between degree-days in October and the incidence of P. graminis (r = 0.65). The incidence of P. striiformis was associated with rainfall in the first halt of August (r = 0.72) and in August (r = 0.69). P. recondita was associated with rainfall in the second half of September (r 0.76) and in September (r = 0.66). P. graminis was correlated with rainfall in the second half of November (r = 0.75) and in November (r = 0.79>. Correlations were also found between P. graminis and rainfall in the second half of July (r = 0.67) and in July (r = 0.58). Biologically it is difficult to explain these last correlations, because this fungus growths much later in the year; but the correlation found between rainfail in July and in November (r = 0.74), explains this apparent association. No other correlations were found in the periods studied.