WSU Extension

Hortsense

Caption: Box blight brown leaf spots
Photo by: J. Glass
  
print version| pdf version| email url    

Boxwood : Box blight
(revision date: 4/11/2018)


Biology
Box blight is a fungal disease that causes leaf spots, stem cankers or black streaks, and foliar blight, and defoliation. Symptoms of blight and defoliation can appear suddenly and affected plants may lose all their leaves. Blighted leaves may be straw- to bronze-colored. White fungal growth may be observed on the underside of the infected leaves. Box blight can be confused with other problems, including boxwood canker. Boxwood canker often infects plants infected with box blight. High humidity or free moisture are necessary for the fungal infection. Planting boxwoods in hedges and/or severely shearing them can result in more disease. Buxus spp. and cultivars, Pachysandra and Sarcococca are hosts.
Management Options

Non-Chemical Management
  • Make certain that the boxwood problem is accurately diagnosed. If box blight is confirmed, destroy infected plants and their debris at the site. Do not compost infected plants.
  • Replant with non-susceptible plants, such as Japanese holly.
  • Space and prune boxwoods to improve air circulation. Disinfect pruning tools.
  • Avoid overhead irrigation.
  • Grow plants in well-drained media or soil with a pH between 6.8 and 7.5. Light shade of 20% can also reduce injury from summer and winter extremes.
Select non-chemical management options as your first choice!

Chemical Management


Fungicides should only be considered if the disease has been diagnosed in the area and only when cultural management strategies are also being used. Fungicides will not cure boxwoods that are infected with blight. Fungicides are only applied to protect against new infections in the spring during bud break through the wet weather. It may be necessary to make a fall application if warm, wet weather is forecast.

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
  • GardenTech Daconil Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 67572-82-71004
  • This list may not include all products registered for this use.
Images
    - hide images

+ Show larger images

 
Caption: Box blight brown leaf spots
Photo by: J. Glass
Caption: Box blight defoliation
Photo by: J. Glass
Caption: Box blight fungus (Calnectria pseudonaviculata)
Photo by: J. Glass