WSU Extension

Hortsense

Lilac
 
Disease
Bacterial blight 
Powdery mildew 
Insect
Lilac borer 
Lilac leafminer 
Oystershell scale 



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Caption: Lilac bacterial blight
Photo by: J.R. Glass
  
Lilac : Bacterial blight
(revision date: 4/11/2018)


Biology
Bacterial blight starts as brown spots on leaves and stems in the early spring. These spots become black with age and cause death of leaves and young shoots, which may bend over at the infection site. Infected older shoots show dying leaves as the infection enlarges along the stem. Flower clusters may also be affected. Infection often occurs on weakened or unhealthy plants and at injury sites such as those caused by wounds and frost damage. Pears, blueberries, cherry, maple, and many other woody plants can also be infected by this blight.
Management Options


Non-Chemical Management
  • Maintain proper plant nutrition. Healthy plants resist disease better.
  • Avoid overhead irrigation.
  • Space plants properly and prune to provide good air circulation. This will slow down spread of the disease.
  • Avoid injuring plants to reduce possibility of infection.
  • Prune and destroy infected tissues as soon as they are noticed.
  • Plant disease-resistant species such as Syringa perkinensis, S. microphylla, or S. vulgaris vars. 'Alphonse Lavallec', 'Crepuscule', 'Floreal', 'Guinevere', 'Jeanne d'Art', 'Lutece', 'Maud Notcutt', 'Mrs. W.W. Marshall', 'Rutilant', or 'William Robinson'.
Select non-chemical management options as your first choice!

Chemical Management

Apply before fall rains and again before budbreak in spring. Do not use Lilly Miller Kop-R-Spray Concentrate for spring applications. 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 Copper Fungicide Spray or Dust RTU [Organic]
    Active ingredient: basic copper sulfate  |  EPA reg no: 4-58
  • Monterey Liqui-Cop Copper Fungicidal Garden Spray
    Active ingredient: copper-ammonia complex  |  EPA reg no: 54705-7
  • Soap-Shield Flowable Liquid Copper Fungicide [Organic]
    Active ingredient: copper octanoate  |  EPA reg no: 67702-2-56872
  • This list may not include all products registered for this use.
Images

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Caption: Lilac bacterial blight
Photo by: J.R. Glass
Caption: Lilac bacterial blight
Photo by: R.S. Byther
Caption: Lilac bacterial blight
Photo by: R.S. Byther
Caption: Lilac bacterial blight
Photo by: C.R. Foss