Pecan Tree "Moss" Is Lichen; Real Problem Is Limb Dieback

Fifty pecan trees have a "mossy" growth on limbs. Affected limbs appear unhealthy and break off. Owner asks how to treat the growth and restore vigor.

The Growth Is Harmless Lichen

Lichens are symbiotic algae-fungus organisms that grow on bark, not in it. They indicate good light penetration—often because the canopy is thinning. They do not cause decline; they colonize after decline begins.

Diagnosing the Dieback

Limb death has many causes in pecan: nutrient deficiencies (Zn, Ni), fungal cankers, borers, root rot, or alternate-bearing stress. The owner should:

1. Examine spring leaf emergence for patterns (tip dieback, rosette, yellowing).
2. Consult the Texas A&M "Evaluating Pecan Problems" guide (linked in original answer).
3. Prune out all dead/dying wood to reduce borer attraction and pathogen spread.
4. Get a soil test ($10–20 via county extension) to tailor fertilization.

Proper nutrition + sanitation pruning often restores vigor. Lichens will persist but are cosmetic.