Fungal leaf spots

Oakleaf hydrangea shows small necrotic leaf spots by mid to late summer. Phyllosticta and Dothiorella species cause minor spotting, usually noticed in midsummer. Avoid overhead watering, space plants for air flow, and clean up fallen leaves. Healthy plants tolerate small numbers of spots; fungicide rarely needed in home landscapes.

Leaf spot and blotch diseases are primarily cosmetic on established plants, though repeated years of heavy infection can weaken them. Rake up and remove fallen leaves to reduce the spore load going into the next season. Avoid overhead watering that splashes spores from the ground onto lower leaves. If the problem is severe, protective fungicide sprays during spring leaf emergence can help, but sanitation does more than chemistry for most leaf spots.