WSU Extension

Hortsense

Caption: Pseudomonas leaf spot on maple
Photo by: R.S. Byther
  
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Maple : Bacterial leaf spot and dieback
(revision date: 4/11/2018)


Biology
Bacterial leaf spot and dieback is caused by the same bacterium which causes bacterial blight of lilacs and many other woody ornamentals. Symptoms include leaf spots, blackening of leaf veins, and tip dieback. Leaf spots are initially small and appear water-soaked. The spots often have a yellowish halo and can expand in size, killing leaves and young seedlings. One-year-old twigs may die back during the winter, or shoots may die back in the spring. The disease is most common on Japanese, Norway, and red maples.
Management Options

Non-Chemical Management
  • Avoid wounding plants.
  • Try to limit pruning to periods of dry weather to reduce infection risks.
  • Remove and destroy dead twigs and infected and fallen leaves.
  • Space plants properly and prune to provide good air circulation.
  • Maintain proper plant nutrition. Healthy plants resist infection.
  • Avoid overhead watering.
  • Plant resistant cultivars. Some Japanese maples show no symptoms of bacterial blight.
Select non-chemical management options as your first choice!

Chemical Management


Use only with cultural controls. Apply in fall to protect wounds and leaf scars, in spring to protect growth. Spring applications must be made under fast-drying conditions to avoid leaf injury. 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.

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Caption: Pseudomonas leaf spot on maple
Photo by: R.S. Byther
Caption: Pseudomonas dieback on maple
Photo by: R.S. Byther