Sycamore canker stain—Ceratocystis fimbriata f. sp. platani
The disease, also called Ceratocystis canker, or sycamore canker, occurs in California, at least in Modesto in the northern San Joaquin Valley. Sycamore and London plane trees (Platanus spp.) are killed by this fungus. In California, infected Platanus usually die within 1 or 2 years after symptoms first appear.
Infection by this vascular wilt fungus causes a sparse canopy of small, chlorotic leaves. Elongated cankers develop in large limbs and trunks. The surface of cankers usually has little obvious callus growth along the margins and commonly appears sunken, dark, and flattened, or covered with discolored or flaky bark. Black fruiting bodies may occur on the wound surface.
Cutting into cankered cambium, phloem, and sapwood reveals dark discoloration, typically bluish black. When a dead branch or trunk is cut in cross-section, wood is often stained in a pie or wedge shape with the tip toward the center of the limb. Stained wood is not soft or rotted, but secondary pathogens may invade and cause wood decay.
No insect vectors of this fungus are definitely known in the United States. Infections at new locations are almost always the result of pruning or other mechanical injuries to trees caused by people.
Ceratocystis produces sticky spores that remain infective for a month or more. Spores spread readily from one tree to another on tools or equipment, including pruning saws that contact infected trees. The fungus also may spread through natural root grafts from infected sycamores to nearby hosts.
Good sanitation and proper cultural practices are the only management methods. No chemicals effectively control this disease. If symptomatic trees are found in areas where the pathogen has not been reported, send samples of freshly infected wood to a diagnostic laboratory.
Prevent injuries to bark from lawn mowers, string trimmers, and anything that wounds trunks or shallow roots. Within several feet of trunks, keep soil bare or apply mulch to avoid the common problem of lawn mower blades or string trimmers scraping the root crown or basal trunk. Where turfgrass or ground covers grow under tree canopies, irrigate properly to encourage deeper root growth. Use relatively infrequent, deep watering when needed instead of frequent shallow sprinkling.
Where the fungus is known or suspected to occur, after pruning any Platanus spp. or using equipment that impacts trees, immediately scrub tools clean with detergent and water and soak them in a 10 to 20% bleach solution. Avoid unnecessary pruning. Except to remove hazardous limbs or dead trees whenever they appear, prune only during dry weather in December and January, when the cold inhibits fungal development.
Promptly remove infected trees and dispose of the wood away from other Platanus spp. Consider trenching at least 2 to 3 feet deep around stumps to eliminate any natural root grafts to nearby Platanus spp.