Boxwood: Box blight

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

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• 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.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• 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.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

• Bonide Fung-onil Multi-Purpose Fungicide Concentrate
  Active ingredient: chlorothalonil [EPA registration number: 60063-9-4]
• ferti-lome Broad Spectrum Landscape and Garden Fungicide
  Active ingredient: chlorothalonil [EPA registration number: 60063-16-7401]
• This list may not include all products registered for this use.

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