Calonectria pseudonaviculata (formerly Cylindrocladium pseudonaviculatum)
Boxwood blight is a serious fungal disease that affects boxwood shrubs (Buxus spp.) and other plants in the Buxaceae family, including Japanese spurge (Pachysandra spp.) and sweetbox (Sarcococca spp.). The disease causes dark leaf spots, stem lesions and rapid defoliation, and can lead to plant death. Because the fungus is easily spread through plant trade and contaminated tools or clothing, early detection and preventive practices are critical to reduce its impact in landscapes and the nursery industry.
Stem cankers from boxwood blight
Leaf lesions from boxwood blight
- History & Distribution
Boxwood blight was first identified in the United Kingdom in the mid-1990s and later in New Zealand. It was detected in the United States in 2011. Since then, reports have documented its presence in many states across the eastern and western United States, including Indiana, where it was first confirmed in 2018. The pathogen continues to spread through plant movement and environmental factors.
- Signs & Symptoms
What to Look For
- Leaf Spots: Dark brown or black circular to irregular leaf spots often appear first.
- Defoliation: Infected leaves may turn brown and fall off rapidly, frequently beginning on lower branches and progressing upward.
- Stem Lesions: Narrow black or dark brown streaks or cankers on stems are a distinguishing sign of boxwood blight.
- Fungal Growth: Under humid conditions, masses of white spores may form on leaves and stems.
- Host Range: All boxwood species are susceptible, though some cultivars show reduced susceptibility.
- Biology & Management
Spores are spread by rain splash and irrigation water over short distances and by movement of contaminated plants, tools, equipment, or clothing over longer distances. Warm, humid conditions favor disease development and sporulation.
Fungus can persist in soil, infected plant material, and debris for years. Remove infected debris and avoid replanting susceptible boxwoods in that location for several years or until disease risk has substantially decreased.
Some boxwood cultivars show moderate resistance, but none are completely immune. Consult extension literature for updated resistance ratings.
- What to Do if You Suspect Boxwood Blight
If you observe symptoms consistent with boxwood blight on plants in Indiana:
- Contact the DNR Division of Entomology & Plant Pathology:
Call 1-866-NO-EXOTIC (1-866-663-9684) or submit photos and descriptions via email. - Plant Diagnostic Confirmation:
Send suspect samples to the Purdue Plant and Pest Diagnostic Laboratory (PPDL) for confirmation. Packaging instructions and submission details are available on their website. Prompt diagnosis can help guide management and limit spread.
- Contact the DNR Division of Entomology & Plant Pathology:
- Resources & Further Reading
- Purdue Extension – Boxwood Blight Publication (BP-203-W) — symptoms, management options, and diagrams.
- National Invasive Species Information Center: Boxwood Blight — national context and additional resources.
- Connecticut Agricultural Experiment Station – Boxwood Blight Info — detailed disease biology and identification.
- North Carolina State Extension – Boxwood Blight Prevention & Management — cultural control and preventive practices.
- Boxwood Blight Task Force - Virginia Tech