Plant care guide
Hydrangea Brown Spots: Cercospora Leaf Spot and Look-Alikes
Updated
Why does my Hydrangea have brown spots?
Small round spots with grey or tan centres and purple or reddish-brown rims on hydrangea leaves are usually Cercospora leaf spot. It starts on the lowest leaves in wet weather and works upward. It is mostly cosmetic and rarely kills the plant.
What to do first
Pick off badly spotted leaves and clear fallen ones, water at the base instead of over the leaves, and water early in the day. Use a fungicide only to protect a plant that had the disease last year, before spots appear.
Brown and purple spots on a hydrangea look worse than they are. On bigleaf hydrangea (Hydrangea macrophylla), the usual cause is Cercospora leaf spot. University of Maryland Extension’s hydrangea problems page calls it unsightly but not fatal, and says it rarely warrants treatment.
The spots won’t go away once they appear. What you can do is slow the spread this season and cut the source for next year.
Is it Cercospora leaf spot?
The spots. Maryland describes tan to grey lesions with dark purple halos. NC State Extension’s hydrangea leaf spot article describes a grey or tan centre with a reddish to purple border. Penn State Extension’s hydrangea diseases page and the UConn Home & Garden Education Center’s hydrangea factsheet describe tan spots with reddish-brown borders.
Where it starts. NC State says infection usually starts on the lower leaves and moves up the plant. It gets worse in wet springs.
When. Maryland says it develops in late summer and autumn. It is more common on newly bought plants grown in crowded conditions, and on plants in poor health.
Look-alikes
| What you see | More likely |
|---|---|
| Reddish-brown or purple spots on oakleaf hydrangea in June, starting low | Bacterial leaf spot |
| Brown, dry edges or whole leaves after heat or drought | Water stress or scorch |
| Pale stippling, fine webbing under leaves | Spider mites |
| White powdery coating | Powdery mildew |
Maryland describes bacterial leaf spot on oakleaf hydrangea (H. quercifolia) in warm, wet weather in late spring and early summer. It spreads upward by splashing water. Treat it the same way: remove low infected leaves early and keep leaves dry. NC State’s bigleaf hydrangea profile also lists leaf spot, bacterial wilt and powdery mildew.
If you see brown edges after hot, dry days rather than round spots, check the soil. Our hydrangea heat wilting guide explains how.
What to do
- Remove badly spotted leaves. UConn suggests removing infected leaves during or at the end of the season.
- Clear fallen leaves. Clemson’s hydrangea factsheet says to remove and dispose of fallen leaves each season. NC State says diseased material goes in the trash, never the compost.
- Keep the leaves dry. NC State recommends drip irrigation rather than overhead sprinklers. Water early in the morning, so leaves dry when the sun reaches them. Penn State and UConn both stress keeping moisture off the leaves.
- Give the plant space. Maryland links the disease to crowded growing conditions. Thin dense plantings so air moves between them.
- Keep the plant vigorous. Maryland says poor health makes it more likely. Water deeply in dry spells; Clemson suggests about once a week.
Do you need a fungicide?
Usually not. NC State says these leaf spots are mostly cosmetic. Infected leaves stay spotted until they drop in winter. Repeated infections over several years can reduce vigour.
Fungicides prevent infection; they don’t cure spots already there. NC State says they work best before the first spots appear. They may need repeating every 10 to 14 days. UConn suggests protectant sprays mainly for plants that had leaf spot before. Clemson and NC State name chlorothalonil, mancozeb and thiophanate-methyl among suitable active ingredients. Use a product labelled for ornamentals and follow the label.
Potted hydrangeas
Gift hydrangeas in pots can get the same spots. The same rules apply: water the compost at the base, not the leaves, and remove spotted leaves. Don’t crowd the pot among other plants. For a potted plant that flags in warm weather, our heat wilting guide explains how to tell thirst from midday droop.
Hydrangeas are a risk to pets if eaten. NC State lists the plant as a problem for cats, dogs and horses.
The hydrangea hub collects our other hydrangea pages. For leaf spot on indoor plants generally, see leaf spot diseases of houseplants.
Related guides
Other hydrangea problems we cover: spider mites.
References
- University of Maryland Extension: Hydrangea, identify and manage problems
- NC State Extension, Union County: Hydrangeas and Fungal Leaf Spots
- Penn State Extension: Hydrangea Diseases
- UConn Home & Garden Education Center: Hydrangea Diseases and Pests
- Clemson Cooperative Extension HGIC: Hydrangea
- NC State Extension Gardener Plant Toolbox: Hydrangea macrophylla
How this guide was put together: University of Maryland Extension, NC State Extension, Penn State Extension, UConn Home & Garden Education Center and Clemson HGIC guidance.