Disease

Boxwood blight

Calonectria pseudonaviculata

A fungus of boxwood, pachysandra and sweet box that spreads fast in warm, humid weather and on tools, clothing and new plants. English and American boxwood can lose all their leaves in a few weeks.

Signs

• Dark brown leaf spots, often with a darker edge.
• Leaves dropping fast, from the bottom of the plant up.
• Dark brown to black streaks on the green stems.

What favors it

Warm (64 to 80 °F, 18 to 27 °C), humid weather, leaves that stay wet, dense plantings, and new boxwood, cuttings or holiday greenery from infected nurseries.

Prevention

• Buy boxwood from nurseries in the Boxwood Blight Cleanliness Program, and keep new plants apart for a month.
• Plant tolerant cultivars; English and American boxwood are the most susceptible.
• Stay out of boxwood plantings when the leaves are wet, and clean tools, tarps and shoes between plantings.

Crops it shows up on

Roses & ornamentals.

Often confused with

Sources

• Best Management Practices for Boxwood Blight in the Virginia Home LandscapeVirginia Cooperative Extension
• Boxwood BlightUMass Amherst Extension
• Boxwood: Identify and Manage Common ProblemsUniversity of Maryland Extension

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