Intense rain will wash off the pesticides residuing on the leafs of vines or other plants. There has been a big improvment of the rain hardness of modern fungicides since 1980. Acutally we can expect the most modern fungicide to resist up to 30 mm of rain if they had a chance to dry on the leaf. If the rain was starting immidiately after the spray or trough the spraing the rain reistence might be widly reduced.
Old fashoned formulations of contact fungicides we have to expect a rain hardness of less then 12 mm. Like we were used to it during the 1970th. To wet the leafes in a vineyard it needs approximately 2 mm or rain. Therefor in this mdoule we only accumulate rains with are bigger than 2mm within one leaf wetness period. This means there might be in total 6 mm of rain during a single day, but this module is not accumulating any of it because the leafs has got dry again befor it was raining 2 mm.
Rain is accumulated for 3, 5 and 7 days. Over longer period plant growth is much more importand for the effect of contact fungicides than rain reistance of the compounds.
In the follwing graph you can see an excample of accumulated rain for February and the first days of March for a iMETOS in a subtropical highland.