Diagnosing Rhododendron Leaf Browning in Atlanta: Disease or Pests?

Symptoms and Possible Causes

A rhododendron developing brown discoloration spreading from the leaf midrib could indicate several issues. In Atlanta's climate, two primary suspects are:

1. Phytophthora Root Rot (Phytophthora ramorum)

• Causes leaf browning, wilting, and dieback.
• More common in poorly drained soils.
• Relatively rare on the East Coast but possible.

2. Spider Mites

• Tiny pests that suck chlorophyll, causing stippling and bronzing.
• Often produce fine webbing on leaf undersides.
• Orthene (acephate) may temporarily suppress them.

Recommended Actions

• Check leaf undersides for mites or webbing.
• Improve drainage; avoid overhead watering.
• Submit a sample to your local Azalea/Rhododendron chapter or county extension for definitive diagnosis.
• If mites: spray horticultural oil or insecticidal soap, covering leaf undersides thoroughly.

Accurate identification is key—treatment differs significantly between a fungal pathogen and an arthropod pest.