Begonia Diseases

Begonias are relatively healthy plants, but their ability to live in low light is just as much of a liability as it is an asset. Limited sunlight promotes damp conditions, which invite fungus. Fungal diseases like botrytis blight and powdery mildew are severe problems for begonias and can stunt growth and even be fatal. Learn how to spot the signs of common diseases to provide treatment and, better yet, attempt to prevent these problems.


Photo by Scot Nelson

Begonia Botrytis Blight

Botrytis blight is a fungal disease that impacts buds, flowers, and foliage. Also known as gray mold, this disease flourishes in damp environments and mainly targets flowers. This infection can hinder growth; if left untreated, botrytis blight can kill begonia plants.

Identifying Botrytis Blight

Brown spots and irregular spots are common signs of botrytis blight. Discoloration appears on flowers and foliage. Infected flowers will have abnormal shapes and often rot before the buds can open. Leaves and stems are usually soft and mushy.

Treating Botrytis Blight

Treat botrytis blight by removing infected growth at the first sign of damage. This fungus can spread and survive cold winter weather, so remove infected foliage to remove the fungus. Properly space plants, as airflow will help prevent fungal growth. When possible, water the soil and keep the plant dry. Fungicides are an option to treat a persistent infection.

Begonia Powdery Mildew

Powdery mildew is a common fungal infection that targets foliage. Infected leaves will wilt as the disease overtakes the growth. The mildew thrives when humidity is high and nights are cool, and will spread throughout a begonia plant and to nearby plants. A severe infection can kill a plant.


Photo by Scot Nelson

Identifying Powdery Mildew

Powdery mildew is whitish-gray and has a fuzzy, powder-like texture. A powdery mildew infection often begins with a few spots. As the mildew spreads, the entire surface of an infected leaf will be covered in a delicate web-like mildew.

Treating Powdery Mildew

Treat powdery mildew on begonia plants by removing infected leaves. Once a leaf is infected, it’s lost, so removal is the best course of action. Burn or dispose of infected foliage responsibly. Do not compost infected plant matter. Spray the plant with a fungicide to kill any remaining fungus that has yet to develop. Crowded, wet conditions are conducive to powdery mildew, so space begonias properly when planting and consider transplanting crowded plants to afford more space. 

Begonia Disease Chart

Botrytis blight Discoloration, mushy stems Prune/discard stems
Powdery Mildew White spots on leaves Proper air circulation


"Begonia." Clemson University Cooperative Extension Service.

"Pests & Diseases in Begonias." American Begonia Society.

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Author Alison Cotsonas - Published 01-09-2024