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Azalea Diseases

Azaleas are lovely flowering shrubs that come in three distinct categories—our gorgeous US natives, Asian evergreens and hybrids. Out of the hundreds of species within each group, all have their own characteristics, but can commonly fall victim to devastating disease. 

Typically fungal in nature, these diseases steal the vibrance of your Azaleas. Below are the predominant ailments that can occur, how you can identify and treat, along with which species may be more resistant or prone to becoming infected.

Azalea Dieback

Also known as Botryosphaeria dothidea, or Phomopsis, and often starts with fungus infecting one branch.

Signs of Azalea Dieback

  • Dying leaves and stems

  • Wood discoloration when peeling back bark of an infected stem

Treating Azalea Dieback

Prune below the discoloration and discard the infectious stems. Be sure to clean your tools well. Thiophanate-methyl or Mancozeb are fungicides that can treat severe cases. But if the plant continues to decline, remove it immediately to prevent spreading in your garden or landscaping.

Powdery Mildew on Azaleas

Also known as Erysiphe polygoni or Microsphaera penicillata, it’s more predominate in Oregon or Washington state.

Signs of Powdery Mildew on Azaleas

  • Yellow misting on leaves

  • Fuzzy white spots on top or under leaves

Treating Powdery Mildew on Azaleas

Assure you’ve planted your Azalea in an area with good air circulation. Pruning can also improve circulation and prevent too much moisture accumulation. Make sure the leaves are receiving adequate sunlight. Use chemical intervention strictly as a last result.

Leaf Spots on Azaleas 

Different types of fungus, specifically Cercospora, Septoria, Phyllosticta and Colletotrichum Species, create dark, misshapen blemishes on leaves. While usually not too serious, leaf spots are an unattractive nuisance. 

Signs of Leaf Spots on Azaleas

  • Spots or “freckles” dark in color

  • Detaching leaves 

  • Reduced overall plant health 

Treating Leaf Spots on Azaleas

Clear out infected leaves, mulch around the base, focus on roots when watering and keep an eye the soil PH level. If worst comes to worst, use fungicides like Copper Hydroxide, Thiophanate-methyl or Chlorothalonil.

Azalea Leaf Gall

Also known as Exobasidium vaccinia and appearing similar to something out of a sci-fi film, the tumor-like disease is known to take hold early spring. 

Signs of Azalea Leaf Gall

  • Pale stems

  • Thick, curled leaves

  • Distorted buds

  • Bulbous growths that eventually brown and harden

Treating Azalea Leaf Gall

Often, fungi growth can be picked off, but severe cases may require Mancozeb, or Chlorothalonil fungicide application.

Azalea Root and Crown Rot

Also known as Phytophthora or “water mold”, rot within azaleas is highly common.

Signs of Azalea Root and Crown Rot

  • Wilting

  • Soggy, weak, black roots

  • Brown discoloration of stems near the base

Treating Azalea Root and Crown Rot

Be sure plants are not seated too deeply, and are in an area with good drainage.

Azalea Petal Blight

Also known as Ovulinia azalea, Petal Blight affects the flowering portion of the plant. 

Signs of Azalea Petal Blight

  • Tiny brown or white dots on flowers

  • Eventually larger, wet openings on petals

  • A quick spreading of the sticky infection from flower to flower

  • Persistence through the winter

Treating Azalea Petal Blight

Remove infected blooms immediately. Water strictly the roots, not allowing the flowers to become wet. Replace the surrounding soil. If needed, fungicides Captan, Chlorothalonil, Maneb, or Triforine can help.

Azalea Botryosphaeria Canker

Scary sounding disease caused by Botryosphaeria dothidea, and does technically create a canker sore.

Signs of Azalea Botryosphaeria Canker

  • Dark, brown holes in the wood 

  • Branch death 

Treating Azalea Botryosphaeria Canker

Be sure soil has good drainage and prune all affected branches. Clean your pruning shears after.

Tip: Reducing overall plant stress will give your botanical babies a better chance of resisting disease 

Azalea Health Checklist 

  • Pick species that suit your area.

  • Don’t plant the roots too deeply.

  • Amend soil with organic matter if planting in dense, poorly drained soil, such as clay.

  • Water the base of the plant to avoid over moistening leaves and blooms. Watering is especially important during times of drought. 

  • Maintain your shrub via pruning and removing dead or troubled looking stems.

  • Always clean pruning shears with a premixed or homemade solution to prevent disease spread.

  • Freeze injury can provoke disease, so protect your plants by wrapping them in breathable but protective burlap.

Azaleas are generally quite hardy shrubs that are highly tolerant, so don’t let these diseases scare you off. Perfect for the gardener with little time, overall they are low maintenance and can be a phenomenal visual addition to your yard.