Lichen on Crabapple: Cosmetic Options If Desired

Same Diagnosis

The green growth is lichen—harmless. It's unsightly to some. If you wish to remove it, spray 3% horticultural oil (dormant oil) or a broad-spectrum fungicide (e.g., Ortho brand) per label. But it will return if canopy remains thin.

Better Approach

Focus on tree health: fertilize, mulch, water. A dense canopy naturally suppresses lichen.