I have an established grape vine which is growing against a south facing brick wall. This year, like last, the leaves have a furry covering on the their undersides which I assume is some sort of powdery mildew. Last year it affected some of the grapes. Can anyone tell me how to prevent/ get rid of this problem? The roots are outside in soil covered by gravel. Is it possible to use some type of spray?
Any help will be gratefully received with thanks.