Boxwood Blight
Calonectria pseudonaviculata (syn. Cylindrocladium pseudonaviculatum, C
4 host plants · Fungal
Last updated
Boxwood blight causes leaf spots with dark centers and yellow halos on boxwood foliage. You'll notice rapid defoliation and stem cankers that girdle branches. The disease spreads via water splash and contaminated pruning tools. Remove infected plants immediately, disinfect all tools, and improve air circulation around plantings.
To limit spread and movement of the pathogen, all confirmed infected plants should be destroyed. Isolate and contain new shipments of boxwood for at least a 30-day observation period.
What Should I Do?
- To limit spread and movement of the pathogen, all confirmed infected plants should be destroyed.
- Isolate and contain new shipments of boxwood for at least a 30-day observation period.
- Locate the isolation area well away from existing blocks or outgoing shipments, and scout weekly.
Quick Reference
Management
Fall through spring in cool wet climates (October-May); March-April peak in PNW.
Cool to mild wet conditions (10-25°C / 50-77°F); rain, overhead irrigation, and dew critical for leaf wetness; sporulation at high humidity (>90%). PNW Handbook cites 10-20°C (50-68°F) for sporulation; OSU EM 9586 (Santamaria 2025) cites 60-77°F (15-25°C) as the mild-wet weather conducive to infection — the higher end of the OSU range may reflect summer infection in irrigated nursery production.
Cultural Controls
- To limit spread and movement of the pathogen, all confirmed infected plants should be destroyed.
- Isolate and contain new shipments of boxwood for at least a 30-day observation period.
- Locate the isolation area well away from existing blocks or outgoing shipments, and scout weekly.
- Break up large blocks of Buxus with non-host species to limit exposure and potential losses due to this disease.
- Do not reuse or recycle or compost infected plants, media, or containers.
- Professional composting is fine.
Boxwood blight was first detected in Oregon nurseries in 2011 and has since been found in at least 16 Oregon nurseries and in landscapes in multiple Oregon counties and in Seattle, WA. The cool, wet maritime climate of the Puget Sound lowlands is highly conducive to disease development. The disease is especially severe where boxwood is sheared tightly into hedges (common in PNW residential landscapes). Management has increased nursery production costs by 25%. Purchase boxwood only from certified, inspected nurseries.