Hydrangea leaf spot

About

Fungal leaf spots are the most common disease of bigleaf hydrangeas in wet years. They look bad by late summer but rarely kill the plant, though years of heavy leaf loss can weaken it.

Also called hydrangea leaf spot, Hydrangea leaf spot, Cercospora leaf spot of hydrangea, Corynespora leaf spot, hydrangea anthracnose

How to recognize it

Symptoms

Small purple spots show first on the lowest, oldest leaves and grow into irregular spots with tan or gray centers and purple to reddish-brown borders, moving up the plant as summer goes on. Badly spotted leaves turn yellow and may drop. Anthracnose makes larger brown dead patches instead.

Often confused with

Cercospora spots are small with purple borders; anthracnose (Colletotrichum) makes larger brown blotches. Both are handled the same way.

Worse when

Long periods of wet leaves from rain, late-summer storms or overhead watering, very wet springs, and bigleaf hydrangeas stressed by too much sun.

How it spreads

Spores form in the spot centers and splash or blow to new leaves; the fungus carries over winter in infected leaves left on the plant or ground.

When

Infection often starts in spring; spots become obvious in late summer and fall, when it is too late to spray that year.

Where

Common in the humid Southeast and Northeast.

What to do, gentlest first

Prevention works best; most sprays only protect healthy leaves and can't cure infected ones. Always read and follow the product label.

1. Keep leaves dry Prevent

   Water with drip or soaker hoses, or water early in the morning so leaves dry fast. Give bigleaf hydrangeas morning sun and afternoon shade.

2. Choose resistant bigleaf cultivars Prevent

   In a Tennessee State University study, 'Ami Pasquier', 'Ayesha', 'Blue Bird', 'Forever Pink', 'Fuji Waterfall', 'Miyama-yae-Murasaki', 'Seafoam', 'Taube', 'Tricolor' and 'Veitchii' resisted leaf spot in sun and shade.

3. Remove spotted and fallen leaves By hand

   Pick off spotted leaves any time, and in fall and winter clean up fallen leaves and any left hanging on the bush.

4. Chlorothalonil, mancozeb, thiophanate-methyl or myclobutanil Conventional spray

   Worth it mainly for young plants or ones badly spotted last year. Start as new leaves open in spring, before spots show, and repeat every 10 to 14 days in wet weather.

   These only protect new leaves. UC IPM rates chlorothalonil high in hazard to people and to fish and other water life: wear gloves, long sleeves and goggles and follow the label.

Plants it affects

Hydrangea, Hydrangea tree (panicle hydrangea), Papaya