Cause Phyllosticta minutissima, a fungus, has been reported from Oregon and Washington. Not considered an economic landscape problem. Spores are thought to be rain splashed.
The fungi Sphaerulina aceris (formerly Septoria aceris) and Xenostigmina zilleri (formerly Cercosporella aceris) are reported to be a common problem on big leaf maple in Washington.
An Alternaria sp. has been a problem in nursery production British Columbia.
Symptoms On different maple species, Phyllosticta spots vary considerably in shape, size, and color. Usually they are small, irregularly circular, and reddish brown with narrow to broad purplish borders. Small, black, fruiting bodies (pycnidia) may be seen in the necrotic areas and may be arranged in a circular pattern. On Japanese maple, which the disease may severely damage, spots are a straw to tan color with a definite margin. The spot's center may be transparent. On sugar and Rocky Mountain maples, spots commonly have a narrow, purplish border. Diseased tissue often falls out, leaving holes in the leaf.
Sphaerulina aceris - Circular, brown spots, up to half-inch in diameter, on the leaves. The centers of the spots become tan-to-cream-colored and bear minute black dots (the fruiting bodies) on the upper surface.
Xenostigmina zilleri - Conspicuous, concentrically zoned spots about an inch in diameter are formed. These often merge to involve a considerable area of the leaf. The central portion of the spot is light brown, the margin dark brown-to-blackish.
Alternaria - Dark-brown-to-black lesions, with or without a yellowish halo.
- Rake and destroy fallen leaves.
- Avoid overhead irrigation that keeps trees wet for an extended period of time.
Chemical control Spray when leaf buds are opening and twice more at 10-day intervals if season is wet. Many of the same fungicides that control anthracnose will most likely control this leaf disease as well.
- Bordeaux 8-8-100. Group M1 fungicide. O
- Daconil Weather Stik at 1.4 pints/100 gal water. Group M5 fungicide. 12-hr reentry.
- Mancozeb-based products. Group M3 fungicides. 24-hr reentry.
- Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
- Orkestra at 8 to 10 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
- Tebuject 16 can be used for tree injections. The number of capsules used is based on tree size. Group 3 fungicide.
References Mayer, J.S. 1987. Triforine controls Phyllosticta leaf spot on silver maple. F&N Tests 42:173-174.
Shaw, C.G., and Harris, M.R. 1960. Important diseases and decays of trees native to Washington. Ag Extension Service, WSU. Extension Bulletin 540.