Blackline
Blackline virus
6 host plants
Last updated
This profile contains verified disease data from extension databases. Regional field notes and expert review are in progress.
A dark line appears in the cambium where scion meets rootstock. Use compatible scion-rootstock combinations. You are most likely to notice symptoms during periods of active growth, particularly when moisture levels favor pathogen development. Early recognition is your best advantage: the sooner you identify the problem, the more effective your management options will be.
Prevention works better than treatment for blackline. Choose resistant varieties when they exist, site plants where air moves freely, and maintain good sanitation by removing debris and infected material. When chemical intervention is necessary, timing matters more than product: apply protectants before the infection window, not after symptoms appear.
Quick Reference
Management
Young grafted trees can acquire the virus immediately after grafting if infected wood is used. Infection via pollen occurs during walnut bloom period (late spring). Trees remain symptom-free for 10-30 years post-infection before vascular collapse at the graft union becomes apparent. Mature trees (15-40 years old) show most dramatic decline and death. Once established, the virus persists for the tree's lifetime. Source: PNW Plant Disease Management Handbook
Symptom expression occurs in susceptible scion and rootstock combinations. Disease severity depends on cultivar compatibility and environmental stress. Trees under water stress or nutritional deficiency may show symptoms more readily. The virus remains latent in asymptomatic carriers and in some varieties showing no external signs despite vascular damage. Source: PNW Plant Disease Management Handbook
Cultural Controls
- Plant disease-resistant varieties of English walnut.
- The variety 'Franquette' is known to be affected by blackline in Oregon.
- Black walnut rootstocks and Paradox rootstocks are resistant.
- Persian walnuts are resistant.
- Do not graft using infected wood.
- Remove and destroy infected trees and grafts.