Identifying and Treating White Fuzzy Growth on Crabapple Trees: Leaf Fungus vs. Borer Damage

A crabapple has white fuzzy growth, first time in 20+ years. Homeowner asks cause and cure.

Two Distinct Possibilities

Fuzz on leaves: Fungal leaf disease (common in high humidity). Treat with Captan, sulfur, or potassium bicarbonate (organic).
Fuzz on trunk/branches: Usually indicates wood-boring insects. Sap leaks, fungus grows on sap. Clean with 1:9 bleach:water, then spray trunk with permethrin.

Take a sample to an independent garden center for confirmation before spraying.

Soil Issues: Bradford Pear Trunk Fungus: Remove and Spray Neem; White Powdery Growth on Oak: Powdery Mildew or Insects?; Crab Apple White Fluffy Growth: Scale or Powdery Mildew?; Crabapple Defoliation: Identify Pest Before Spraying; Cedar-Apple Rust and Fruit Safety: Edible with Spot Removal; Apple Scab and Cedar-Apple Rust on Ornamental Crabapple; Diagnosing Red Mounds on Ornamental Crabapple; Stopping Tree Sprouts After Cutting Down Crabapples; White Fungus Under Crabapple: Fungicide Strategy for Replanting Success; Crab Apple Defoliation from Mold: Fungicide Spray — Prevents Repeat

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