Arborvitae Black Foliage: Overwatering, Aphids, or Foliar Disease

Arborvitae with black foliage; owner surprised expert deferred.

Leads

• Overwatering → fungus (black sooty coating). Drought: water ≤1×/week.
• Aphids + sooty mold (black fungus on honeydew).
• Foliar disease (e.g., Pestalotiopsis).

Take sample to nursery or county extension horticulturist for ID. Expert focuses more on trees than shrubs.