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New Japanese Maple Brown Leaf Spots: Phyllosticta Leaf Spot

Diagnosis

Brown spots with purple-red borders on new Japanese maple in windy shade = Phyllosticta leaf spot (fungal). Spots may develop black rings (fruiting bodies) later.

Management

Usually cosmetic; minimal health impact.
If desired, spray fungicide (mancozeb or chlorothalonil) on new leaves every 14–21 days in spring.
Improve airflow, avoid overhead watering.

Rarely warrants treatment on landscape trees.

Plant Diseases: Identifying Lichen vs. Disease on Maple Trunks and Managing Frost Cracks; Phyllosticta Leaf Spot on Japanese Maple: Cosmetic Late-Season Fungus; Bark Peeling on Mature Japanese Maple: Sunscald or Something Else?; Maple Spindle Gall Mites: Yellow Spikes Are Cosmetic; Phyllosticta Leaf Spot on Maple: The 'Lunar Eclipse' Fungus; Japanese Maple Leaf Spots: Phyllosticta (Purple Eye); Maple Leaf Spot: Phyllosticta—Mostly Cosmetic; Maple Leaf Spot: Phyllosticta Diagnosis and Management; Japanese Maple Leaf Spots: Phyllosticta Fungus — Mostly Cosmetic; Japanese Maple Tree Diseases: Identification and Treatment

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