Phytophthora Root and Crown Rot
Phytophthora cinnamomi
4 host plants
Last updated
This profile contains verified disease data from extension databases. Regional field notes and expert review are in progress.
Root and crown rot caused by Phytophthora appears as wilting, decline, and eventual death of affected plants. Once established in soil, this disease is difficult to eradicate. Rotate to new land or grow resistant varieties if you want to return to planting. Remove infected plants immediately. Ensure excellent drainage to prevent future problems. Proper drainage and good site selection are critical to prevent root disease problems. Monitor plants for early signs of decline or wilting.
Avoid reusing pots from a previous crop. If pots must be reused then wash off all debris and soak in a sanitizing solution or treat with aerated steam for 30 min.
Quick Reference
Management
Most active during warm, wet periods (spring and early summer when soil stays saturated). P. cinnamomi optimal at 65-85°F. In the Puget Sound region, peak activity typically April-July when spring rains combine with warm temperatures. Secondary peak in fall (September-October) if conditions remain wet and warm. Minimal activity in cold winters or dry summers. # Source: PNW Plant Disease Management Handbook
Poor soil drainage; overwatering; warm temperatures (65-85°F optimal for P. cinnamomi); prolonged soil saturation; contaminated potting media or irrigation water; clay-heavy soils; inadequate mulching or gravel drainage under containers. # Source: PNW Plant Disease Management Handbook - Phytophthora Root and Crown Rot (Boxwood)
Cultural Controls
- Avoid reusing pots from a previous crop.
- If pots must be reused then wash off all debris and soak in a sanitizing solution or treat with aerated steam for 30 min.
- Provide good drainage for plants in beds, fields, or containers.
- Place containers on gravel beds (4 inches or more deep) to allow drainage.
- Do not place containers on poly sheets; they can prevent containers from draining and allow contaminated drainage water to spread from the base of one container to another.
- Avoid planting in areas where boxwood and other Phytophthora hosts have previously died.