Lilac: Bacterial blight

• Categories: Lilac Lilac Diseases Ornamentals Shrubs
• Last review date: 2026-07-31 02:12

Biology

Bbacterial 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

See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.

Non-chemical Management

Select non-chemical management options as your first choice!

• 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’.

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.

Approved Pesticides

If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.

• Bonide Copper Fungicide Spray or Dust RTU [Organic]
  Active ingredient: basic copper sulfate
  EPA registration number: 4-58
• Monterey Liqui-Cop Copper Fungicidal Garden Spray
  Active ingredient: copper-ammonia complex
  EPA registration number: 54705-7
• Soap-Shield Flowable Liquid Copper Fungicide [Organic]
  Active ingredient: copper octanoate
  EPA registration number: 67702-2-56872
• This list may not include all products registered for this use.