Phytophthora Root & Crown Rot 🦠
At a glance
- Cause: Soilborne water mold favored by wet, poorly drained soil
- Tell-tale sign: A plant wilts or declines even though the soil has been wet
- Severity: Serious — prevention matters far more than rescue
How to identify
Phytophthora problems look like water stress in reverse: the plant wilts, yellows, thins, or collapses while soil has been wet. Roots may be dark and rotted, and crowns or lower stems can show brown cankers near the soil line. In landscapes, affected plants often sit in a drainage problem, irrigation overspray zone, compacted soil, or low spot.
What causes it
Phytophthora species are water molds that move in wet soil and attack roots and crowns. California natives adapted to dry summers can be especially vulnerable when irrigated like conventional landscape plants.
Treatment & management
Following Integrated Pest Management:
- Fix water first: reduce irrigation, improve drainage, and keep water away from crowns.
- Remove dead or collapsing plants and avoid moving contaminated soil.
- Do not replant the same susceptible species into the same wet spot without solving drainage.
- For containers, discard contaminated mix and sanitize pots before reuse.
- Professional diagnosis and treatment may be worthwhile for valuable trees or landscapes.
Prevention
Plant high, use sharp drainage, avoid summer irrigation on dry-summer natives, keep mulch away from trunks/crowns, and do not move wet contaminated soil between sites.
Affects (in this guide)
Coast Live Oak, manzanitas, many California natives in irrigated landscapes, fruit trees, and ornamentals