Botrytis Bunch Rot Gray Mold
“Botrytis cinerea”
2 host plants · Fungal
Last updated
This profile contains verified disease data from extension databases. Regional field notes and expert review are in progress.
Botrytis bunch rot affects fruit clusters of Oregon grape and mahonia, particularly during wet springs in cool, humid climates. Gray mold develops on fruit touching fruit and on injured berries that provide entry points for spore germination. The fungus thrives in dense canopies where moisture lingers, making it most visible around harvest time and in years with humid weather.
The vulnerability window is narrow but critical: disease establishes during fruit set and flowering when dense canopy conditions trap moisture around developing fruit. Your prevention strategy is straightforward; space plantings generously and prune to open the interior for air movement, avoid overhead irrigation, and prevent any fruit damage that could invite fungal entry. Clean up all debris including mummified fruit at season's end.
Quick Reference
Management
Bloom period (primary risk through flower infection); early fruit development through ripening in cool, wet weather; post-harvest storage period in cool, humid conditions.
4-6 hours continuous leaf wetness at 60-77°F (15-25°C); optimum 65-73°F. Tight fruit clusters and dense canopy foliage trap moisture and suppress drying. Rain or overhead irrigation during bloom and fruit development creates ideal infection conditions. Cool, wet springs favor disease. # Source: PNW Plant Disease Management Handbook
Cultural Controls
- Space plantings and prune to provide good air circulation and reduce humidity.
- Avoid overhead watering and other practices which cause moist conditions in the canopy.
- Prevent injury to the fruit, which can facilitate disease development.
- Clean up plant debris, including mummified fruit.
- Destroy or discard (do not compost) diseased materials.