Stem Rot

Stem rot caused by Phytophthora creates dark brown to black cankers on stems and crowns of crabapples, peonies, and dianthus, typically appearing on the lower portions of plants. You may notice an alcoholic odor coming from infected bark, and the leading edge of a canker often looks irregularly mottled. In winter and early spring during cool, wet weather in Western Washington, this disease can spread rapidly through nursery stock and young trees.

Prevention is far more effective than trying to treat stem rot once it takes hold. Plant on well-drained sites, never mound soil against tree trunks, and remove trees from wet ground storage quickly. If you're moving nursery stock, keep trees off the ground during rainy weather and never heel them in deeper than the original collar line. Chemical options like phosphonate sprays can help prevent infection if applied before the disease arrives.