Common names:
- Boxwood blight
- Box blight
- Boxwood leaf drop
- Blight disease of boxwood
Pathogen causing this disease:
- Calonectria pseudonaviculata
Conducive conditions
Weather conducive to disease:
- High humidity
- Mild, wet weather (60˚F – 77˚F)
- Rain splashes spores in the soil and on fallen leaves to the foliage of other plants
Practices conducive to disease
- Watering too frequently
- Tightly packed pots
- Plants shaded by structures and buildings
Likely infection conditions
- Moisture on leaves for long periods of time
- High humidity and free water present
Mechanisms of spread
Litter transported on vehicles, feet and equipment
Infested leaf litter (microsclerotia & conidia)
Introduction through infected plants
Equipment, gloves, tools
Conida on infected foliage
Spread from animals
Symptoms
Dark spots with darker margins. May grow together to form large lesions or entire leaf may turn gray to black.
The center of the leaf lesion may turn tan. Yellow halos may appear.
Leaves look bronzed and begin to fall off (defoliate).
Stem lesions are dark and linear to diamond-shaped; may start at the bottom of the plant.
Stems may appear bare if all leaves have fallen.
Spores will form sticky white mass on undersides of leaves and stem.
Scouting tips
Where to look?
- Disease will often begin from the interior or lower canopy of the plant.
- Move outer leaves and upper branches aside to inspect those locations carefully.
- These areas stay moist for longer and are more prone to infection.
What to watch for:
- Symptoms may be mild, but still present during summer months.
- Overhead irrigation increases the risk of disease.
- Symptoms become more apparent during the wet weather from fall through spring.
- Scout for disease year-round.
- Check greenhouses often, since they foster conditions for disease development.
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