Hydrangea Diseases – Common Hydrangea Leaf Problems
While hydrangeas are adored for their impressive blooms rather than their foliage, hydrangea leaf problems can certainly ruin the aesthetics of these beautiful shrubs and have implications on the health of blooms as well.
Leaf problems can appear on any garden plants or shrubs including hydrangeas. To help you diagnose and treat common leaf problems in hydrangeas, it’s important to identify the underlying cause.
Below, I discuss the leaf problems of hydrangeas, how to identify them and what types of remedies are available. Luckily, most problems are avoidable or treatable.
Common Problems with Hydrangea Leaves
From yellowing leaves to fungal diseases, hydrangeas can suffer a wide range of leaf problems. Some of these can cause the discoloration of the leaves, others cause deformity.
Leaves can also fall off if the damage is extensive. But you may also need to remove some of the sections of the plant yourself, either because they’re unsalvageable or to prevent further spread.
Here are the leaf problems to watch out for:
– Yellow Leaves
Yellow leaves on hydrangeas can signal a number of underlying causes such as dehydration, overwatering, and fertilizer burn.
Yellowing leaves are a symptom of these problems causing parts of the root system to die off. Leaves first turn yellow, then they may turn brown, eventually falling off.
Yellowing leaves can also be caused by temperature changes and seasonal changes.
To prevent leaves from turning yellow, make sure you understand the watering and fertilizing needs of hydrangea plants.
Moist but not wet soil and infrequent fertilizing are key to the health of your hydrangeas.
– Curling Leaves
Curling hydrangea leaves are usually caused by dehydration or fungal diseases. Dehydration is more prevalent in summer if temperatures rise and there is no rainfall.
But fungal problems that affect the roots — like the Armillaria — can cause root rot and indirectly cause dehydration in hydrangea leaves.
But there are other fungal diseases that attack the foliage and cause leaves to curl. The Cercospora fungus is a common culprit for curling leaves.
To prevent dehydration of hydrangeas, make sure to water deeply whenever leaves start to look droopy.
Fungal problems, once detected, can be treated by spraying the leaves with a fungicide.
– Brown Leaves
Brown leaves are usually caused by fertilizer burn or by excessive sun exposure. When a hydrangea is overfertilized, leaf tips and leaf edges can turn brown.
If a hydrangea that’s not accustomed to direct sunlight (like a potted hydrangea that you’re moving outdoors) sits in direct sunlight for too long, its leaves can turn brown.
If you suspect that you’ve overfertilized your hydrangea, you should flush the soil with water to wash away as much of the mineral salts as possible. After flushing, withhold watering for a few days, and then resume normal watering.
Don’t fertilize the plant again until it bounces back to normal health. Whenever you fertilize hydrangeas, pay close attention to dosage recommendations and don’t fertilize them often.
– Brown Spots
Brown spots on hydrangeas usually appear because of a bacterial infection, commonly with the bacteria known as Xanthomonas campestris.
There are three types of hydrangeas that are more prone to be affected by bacterial leaf spots — Hydrangea quercifolia, arborescens and macrophylla.
The problem can be first noticed on the leaves at the base of the plant. Spots start out as red or purple and are dispersed on the entire surface of the leaves. Spots close to the veins are usually angular in shape.
Brown spots can also be caused by fungal problems. The fungi Cercospora hydrangea and Colletotrichum gloeosporioides (which causes the fungal disease Anthracnose) are the most common fungi to affect the leaves of hydrangea plants.
You can distinguish the two types of fungal problems by the color, size and shape of the brown spots.
If the brown spots are small, around 1/8 to 1/4 inches in diameter, with gray or tan centers and purple or brown halos or the entire leaf is purple-brown, then you’re dealing with Cercospora leaf spot.
If the brown spots are large with tan spots or light brown spots in the center, your hydrangea leaves are affected by anthracnose.
Regardless of the causative fungal problem, the treatment is the same — spraying the leaves with chlorothalonil and thiophanate-methyl based fungicides.
Some of the best ways to prevent bacterial or fungal brown spots is to keep hydrangea shrubs well-aerated by deadheading spent blooms, keeping the base of the plant free of leaf debris and dead canes.
Also, avoid watering your hydrangea from above, water at the root level instead to avoid getting water on the leaves. Moisture on the leaves can cause fungal diseases.
– Holes on Leaves
Holes on the leaves are most likely caused by a pest problem. Slugs and snails are the primary culprits. You may also notice that the edges of your hydrangea leaves are also ragged and chewed up.
Besides snails, beetles can also feed on the leaves of your hydrangeas, causing massive foliage devastation. Blooms can also be affected, especially by beetles.
Therefore, a few holes on your hydrangea leaves may not be an immediate cause for concern, but it’s important to identify the cause and take measures to prevent further damage.
Slugs and snails are best removed by hand, but since they’re most active during the night, you may not notice them during the day. Beetles can also be removed by hand.
Spraying your hydrangeas with dish soap and water mixture or using slug traps can also work. Insecticides should be a last resort treatment against these pests.
– Powdery Mildew
If you notice a pale or gray, powdery coating on your hydrangea leaves, it’s highly likely that it’s a fungal infection called powdery mildew.
Multiple fungi that spread through spores are responsible for this disease including Oidium hortensiae, Erysiphe poeltii, and Golovinomyces orontii, just to name a few.
Sudden changes in temperature are believed to be one of the triggering events of this fungal leaf disease.
One of the best ways to stop the spread of the disease is to remove affected leaves and sections of the plant. Spraying the plants with neem oil and being mindful of a few preventative measures can reduce the incidence of this disease.
As I mentioned before, when I discussed preventing fungal leaf problems, keeping water off the leaves is one way to deal with fungal infections. Water the base and water in the morning, so that any moisture on the leaves has enough time to dry before the night.
– Drooping Leaves
Drooping leaves is usually a sign of dehydration and a signal that it’s time to water your hydrangea. You may notice drooping leaves in summer. Check if the soil of your hydrangeas is also dry.
In summer, you need to pay close attention to the hydration level of hydrangea bushes. The soil must be kept moist and never be allowed to become bone dry.
Dropping leaves can also appear if there are sudden changes in temperature such as when warm days are followed by cold ones.
– Hydrangea Rust
Orange spots on the underside of leaves signal a hydrangea rust problem, which is nothing else but another fungal disease that can affect hydrangea foliage.
The fungus responsible for hydrangea rust is called Pucciniastrum hydrangeae. With time, affected leaves will change color to brown and fall off.
As with other fungal problems, prevention is key. Keeping moisture off the leaves when watering and making sure the hydrangea bush is well aerated are the gold standard in preventing this fungal disease.
As for the treatment of hydrangea rust, there are a few things you can try:
- Remove affected leaves or parts of the plant
- If entire sections are affected, remove damaged sections
- Use neem oil to spray the leaves of the plant (you can use it as a remedy to hydrangea rust, but also as a preventative)
- Spray with other organic fungicides
Whenever possible, choose organic fungicides and insecticides to limit the harmful effects of these chemicals on the environment and beneficial insects such as pollinators.
Remedies don’t act immediately. They need to be reapplied over longer periods, usually until the problems go away. Fungal problems are difficult to treat, especially when they’ve already spread.
Remember that preventative measures can do a lot to minimize bacterial and fungal diseases.
There are plenty of problems that can affect the leaves of hydrangeas. Some of these problems are easy to prevent, others may be completely out of your control.
Fungal and bacterial infections can be avoided if you pay extra attention to how you water your hydrangeas (always at the base, never from above) and to keep the shrub well-aerated.
Insect problems can be more difficult to avoid since insects are naturally attracted to plants. In case of insect attacks, you should act as soon as you discover the problem to avoid a full-blown infestation that could potentially decimate your hydrangeas.
All in all, most hydrangea leaf problems are manageable, treatment options are available, all you have to do is monitor the health of the leaves and apply remedies whenever necessary.