Crown and Collar Rot
Phytophthora cactorum (primary), P
14 host plants · Oomycete
Last updated
Crown and collar rot causes decay at the base of infected plants near the soil line. You notice soft, mushy tissue that may exude liquid or develop foul odor. The disease favors wet soils and poor drainage. Improve drainage, avoid wounding, and remove severely infected plants.
Water management that minimizes excessive water around the root crown is critical for management of this disease. Locate orchards on well-drained slopes if possible.
Quick Reference
Management
Symptoms typically appear in early fall, when one or more branches show signs of decline. In the Puget Sound region, risk is highest during wet periods in spring (April-June) and fall (September-November) when soils are saturated or waterlogged. P. cactorum is most active at cooler temperatures (50-70°F). # Source: PNW Plant Disease Management Handbook
Poorly drained soils; excessive water around root crown; low-lying orchard sites; heavy clay soils; irrigation water pooling at trunk bases; susceptible rootstocks
Cultural Controls
- Water management that minimizes excessive water around the root crown is critical for management of this disease.
- Locate orchards on well-drained slopes if possible.
- Tile orchards or sites with poor drainage.
- Plant on a raised bed to help keep water away from trunks.
- Use resistant rootstocks. 'Antonovka', 'McIntosh', and 'Wealthy' apple seedlings, and M9 clonal rootstocks, as well as B9 and advanced selections in the Geneva series have shown high resistance to collar rot.
- Avoid the application of too much irrigation water.