Ramorum leaf and shoot blight (Sudden oak death)

You'll notice leaf spots and twig dieback on susceptible ornamentals like camellia, pieris, and rhododendron, particularly in fall and winter when humidity stays high in Western Washington. The disease appears first as tan or brown lesions on leaves and shoots, which may enlarge rapidly, especially during wet, cool weather. Infected twigs show a characteristic brown canker, and severely affected branches die back. This is a regulated pathogen in the Pacific Northwest; early detection matters because infection spreads through water splash and contaminated soil.

Phytophthora ramorum doesn't just damage your plants, it threatens native oak species in forests across the region, so it's worth taking seriously even in a home garden. The pathogen lives in soil and water, making prevention your main defense. Buy nursery plants carefully (insist on disease-free stock), inspect before purchase, and quarantine new plants for 4 to 6 weeks away from established plantings. Avoid overhead watering and clean up fallen leaves and cankered wood promptly; these simple practices interrupt the disease cycle and protect both your garden and the broader ecosystem.