White substance on the trunk of my lilac bush
The white patches shown in the photo are a kind of toothed crust fungus that often grows on dead and dying wood. It's presence suggests that the lilac trunk's days are probably numbered.
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When wood rot is present, nothing can be done to cure it. Some woody plants affected by fungal decay live for a long time but watch for evidence of its effects. Decaying trunks and branches that fail unexpectedly can be hazardous.