Ornamental maple trees are subject to a variety of leaf spot diseases, most are a fungal disease, but there are also bacterial diseases. With deciduous trees, each growing season brings a new crop of leaves and infection often occurs soon after buds burst and new leaves emerge. And each new growing season is a new opportunity for keeping leaves healthy.

The first line of defense to reduce risks is often to 1) Rake and destroy fallen leaves; 2) avoid overhead irrigation that keeps trees wet for an extended period of time: and 3) if there are twig or stem cankers associated with fungal leaf spots, remove and destroy these during dormant season pruning. Once you have a specific identification of a fungal leaf disease there are also chemical fungicide treatments that may apply.

For example see the article in the PNW plant disease handbook at

To pursue definitive identification of the disease in your case, please contact the OSU Master Gardeners in Clackamas County at <personal data hidden>, call<personal data hidden>, or visit the office at 200 Warner Milne Rd. in Oregon City.