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Maple : Phyllosticta leaf spot
(revision date: 4/11/2018)


Biology
Symptoms of Phyllosticta leaf spot on many maple species include the development of small (approximately 1/5 inch), roughly circular, brown spots with dark reddish or purplish borders. Japanese maples develop yellowish or tan spots, which sometimes have transparent centers. A circular pattern of black fungal fruiting bodies may be seen in the dead areas on infected leaves. On some maples, the diseased center portions of the leaf spots may fall out, giving a shothole appearance to the leaves. Infection occurs on wet leaves by water-splashed spores. Wet weather in spring and early summer favors disease development. The fungus probably overwinters on fallen leaves or on buds and twigs of host trees. This disease is not considered a serious landscape problem.
Management Options

Non-Chemical Management
  • Rake and destroy fallen leaves.
  • Avoid overhead irrigation. If it is necessary to use overhead irrigation, water when foliage can dry quickly.
Select non-chemical management options as your first choice!

Chemical Management


Apply when leaf buds are opening and twice more at 10-day intervals if season is wet. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Bonide Fung-onil Multi-Purpose Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 60063-9-4
  • ferti-lome Broad Spectrum Landscape & Garden Fungicide
    Active ingredient: chlorothalonil  |  EPA reg no: 60063-16-7401
  • This list may not include all products registered for this use.
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