Brown Spots on Hydrangea Leaves
Causes and solutions
A Look at what causes brown and purple spots on hydrangea leaves
By the team at DIY Gardening
Welcome to another entry in our Pest Control Series. This guide to hydrangea leaf spots and solutions was created by Hannah Miller, a keen amateur gardener who is currently growing six hydrangeas, including two beautiful Macrophylla Ab Green Shadows.
Hydrangeas are very popular ornamental plants that are usually grown for their large flower heads that bloom from spring through to autumn. The foliage is also attractive with many hydrangeas producing large dense leaf formations.
Black, purple and brown spots on hydrangea leaves can ruin the appearance of this popular plant, making it look sickly and detracting from the beauty of the blooms.
On this page, we’ll discuss the most common causes of spots on hydrangea leaves and what you can do about them, which includes several recommended products.
Two Common Fungal Diseases That Affect Hydrangea Leaves
Here are the two most common fungal diseases affect hydrangea leaves, the symptoms are very similar for each:
1) Cercospora Leaf Spot – this is a widespread fungal disease that can affect many hydrangea plants. The first sign of infection will likely be brown or purple spots, often circular, around 3-6mm and scattered on different parts of the leaf and on random leaves. Cercospora is often seen on hydrangea leaves in autumn and is in part caused by the more moist conditions found at this time of the year.
2) Anthracnose – while not as common as Cercospora, Anthracnose also produces large brown, black and purple spots on hydrangea leaves, most often on big leaf hydrangeas such as macrophylla. The spots may have rings outside them and a bullseye in the centre. They may also be angular, rather than circular. Unlike Cercospora, you may also see Anthracnose spots on the flowers as well. Excessive use of fertiliser, especially in hydrangeas grown in containers, can increase the severity of Anthracnose.
Risk to Hydgrangea Health
Cercospora Leaf Spot is so common in autumn that many gardeners choose to ignore it. The fungal disease is unlikely to kill the hydrangea plant so late in the year and any fungal treatment won’t have time to work. Cercospora can cause stunted plant growth but is unlikely to kill the plant.
Anthracnose is more severe than Cercospora and while most cases do not kill the hydrangea, some do.
Both fungal infections can lead to leaf damage, reduced photosynthesis and growth issues.
Causes of Brown Spots on Hydrangea Leaves
There are several causes of brown hydrangea leaf spots/fungal disease:
- An unusually wet summer and autumn can create an environment where the leaves are wetter for longer and don’t dry out so quickly. This encourages fungal growth which then spreads exponentially. It’s not uncommon to see brown fungal leaf infections after a period of damp autumnal weather, even fog and morning dew at this time of year can exasperate the condition.
- The location of the hydrangea should be considered as these plants need good airflow for the leaves to dry out. Place the hydrangea next to a wall in a very shaded part of the garden, and the leaves might become susceptible to fungal growth.
- Overhead watering is perhaps one of the most common causes of fungal disease in hydrangea leaves. Not only does this soak the leaves, but the splash helps to spread the fungus, the brown spots on the hydrangea leaves than multiply and grow.
- Hydrangeas shouldn’t be watered in the evening as at night, any moisture on the leaves won’t evaporate so quickly, and the leaf surface may be susceptible to fungal growth and spread.
- It would be best if you observed good hygiene when pruning hydrangeas as fungal infections, which are often invisible at first, can spread via hands and secateurs.
Solutions – How to Get Rid of Brown Spots on Hydrangeas
Here’s a checklist for you to follow if you’ve seen brown spots on your hydrangeas:
- If you’ve noticed a few brown spots on the hydrangea leaves after a period of wet weather in late summer or autumn then don’t panic, this is normal. The fungal pathogen is widespread and can be found in most gardens just waiting for the right weather conditions.
- Go through the plant and remove the most infected leaves, dispose of them in the trash and not in the garden, you don’t want to reinfect the plant.
- Check that the hydrangea is located in a good position. Avoid areas that are overly damp and where there’s little airflow. Hydrangeas grown next to walls and crowded by other plants should be relocated.
- If the hydrangea is very dense due to a lack of pruning, remove some stems to increase the airflow through the plant.
- Stop watering hydrangeas overhead and switch to watering at ground level to prevent water from splashing onto the leaves and transferring the fungus to more leaves.
- Water in the morning and not in the evening so the leaves have a chance to dry out before nightfall.
- Periodically remove any fallen leaves from the base of the plant, the fungus could reinfect another part of the plant if left to decompose in the soil.
- When pruning hydrangeas, always wash your secateurs with a mixture of water and bleach or give them a wipe with an alcohol swab. Be careful when touching hydrangeas that are showing signs of fungal infection, the spores spread very easily via hands and cutting tools.
- If the infection is particularly nasty, apply a leaf fungicide every two weeks from spring through to autumn. There’s no point in trying to clear up an infection later than mid-autumn, so start the following spring. Fungicides won’t remove the brown spots from existing hydrangea leaves but can act as a deterrent on new leaves if applied early enough in the year.
- Destruction of hydrangea plants due to fungal infections is rarely needed but if you’re concerned about the disease spreading to nearby plants, it should be considered.
1) FungusClear Ultra (Our Recommendation):
- Contains Triticonazole which experts suggest is the best chemical fungicide for treating Anthracnose infections.
- Also effective against Cercospora fungal infections.
- Great reviews online (read them here).
- Successfully tested by us here at DIY Gardening.
- Stops leaf spots from spreading and forming on new leaves.
- Apply every 2-3 weeks.
2) Garden Protect Fungicide:
- Is a general purpose leaf and stem fungicide.
- High copper content so is effective on hydrangea leaves.
- Can be used on a variety of crops and ornamental plants.
- Will not stain leaves or flowers.
- Use every 10 – 14 days.
3) Organic Neem Oil:
- Is 100% organic.
- No chemicals.
- Effective fungicide for general use in the garden.
- Works well on leaf spots if applied frequently.
- Test on single infected leaf first to see if it’s safe to use and won’t damage the plant.
Note: None of these products will remove existing leaf spots but will prevent them from spreading and forming on new leaves, so apply during periods of growth from spring to early autumn.
Hydrangeas are considered by many gardeners to be one of the best low-maintenance garden plants, and if grown in the right location, watered correctly and handled with care, they can live for years without any issues.
Fungal infections can be common, and nothing to worry about or they could be a sign of a more severe issue that requires action on your part.
Brown, black or even purple spots on hydrangea leaves are unlikely to kill the plant but can stunt its growth for that year. You should assess the plant to determine the cause so the hydrangea can be nurtured back to full health.
Regardless of the type of fungal infection, follow the steps suggested in this guide and we’re confident you can stop the brown spots from appearing on new hydrangea leaves.
Hannah’s insightful guide to growing hydrangeas in pots is a must-read if you’re new to growing these shrubs and want to try growing them in a container.
Nursery Mag has a guide to Cercospora leaf spot that’s worth exploring, it explains the conditions that help this disease to spread.
Article about treating leaf spot in hydrangeas by a pathologist at the University of Arkansas.
When is the best time to apply a fungicide?
The fungal infection could be present for several weeks before it’s visible to the naked eye so apply the fungicide from spring.
How often should the fungicide be applied?
Always follow the instructions on the label, but most fungicides should be applied every 10 – 21 days from spring up to early autumn.
How many leaves or stems can I remove from an infected hydrangea plant before it dies?
Most hydrangeas can survive if up to one-third of their foliage is removed, any more than this and the plant may not recover, especially if some of the remaining leaves are infected.
Are there any other causes of brown leaf spots on hydrangea plants?
Other, less common bacterial infections may cause leaf spots and discolouration, as can root damage, transplant shock and over-fertilisation, although other symptoms are usually present. Brown leaf spots are most often caused by the two fungal infections discussed in this article.
Where did the fungus that causes brown leaf spots come from?
The fungus spores are present in most gardens but rarely reach a stage where they grow uncontrollably. Moist, warm weather, lack of ventilation and overhead watering can cause them to spread exponentially to a point where they are destructive and difficult to manage.
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