Artificial rainfalls were used to determine the effect of the amount of the
rainfall and the time interval between pesticide application and rainfall
event, on folpet and mancozeb residues on grapes and vine leaves. Forty-fiv
e mm of rain were administered to the vineyard in different amounts (45; 30
+15; 15+15+15 mm). Folpet showed good rainfastness on the grapes and on the
leaves. A modest decrease was observed only in the experiments that had re
ceived 45 mm of rain at one go. Mancozeb showed a lower rainfastness, since
a portion of the deposit was easily washed off also by a modest rainfall.
The percentage of this portion was higher in the grapes (38%) than in the l
eaves (20%). The data obtained in these experiments show that, in the case
of folpet, it is not necessary to repeat the treatment when it rains the da
y after, while it is recommendable to repeat it in the case of mancozeb.