There are a couple different fungal species which cause a brown to copper
colored leaf spotting on hydrangeas. In general, these diseases are not
serious. They may make the plant look
unsightly but will not kill the plant. Like many of the diseases in rainy
areas, the reality is the more the rain, the worse the disease. (This is due to
the rain droplets spreading the spores from leaf to leaf and plant to
plant). Leaves that are badly affected
should be removed. A copper fungicide spray
could be used to help prevent the spread. Keep in mind that after several
inches of rainfall, the protective copper will wash off.
