13 Hydrangea Diseases With Pictures

Hi, friends! Today, I will tell you about the most common hydrangea diseases and how to deal with them.

Cercospora Leaf Spot

Cercospora leaf spot is a common hydrangea disease that rarely kills the plant but poses a greater threat to young specimens.

Infections typically begin in summer, though symptoms often don’t appear until fall. The fungus first attacks the lower leaves and gradually spreads upward.

Symptoms

1. Small circular spots—less than a quarter inch across—form on the leaves. These spots are usually brown but may vary in color depending on the hydrangea variety and growing conditions.
2. When the infection is severe, the leaves may yellow and eventually fall off.

Control

1. Provide ample spacing between plants to improve air circulation and help foliage dry quickly.
2. Avoid overhead watering and prolonged leaf wetness.
3. Always use clean, sterilized tools when pruning.
4. Keep the area around the plant free of fallen debris and diseased leaves.
5. Remove and discard all infected leaves promptly.
6. Finally, apply a fungicide containing chlorothalonil or thiophanate-methyl to control the spread of the disease.

Anthracnose

Anthracnose is a common fungal disease that affects hydrangeas and many other plants. Although it rarely kills the plant, it can cause noticeable damage and reduce its visual appeal.

Symptoms

1. The first signs of anthracnose are irregular spots of different sizes and shapes on the leaves.
2. Over time, black or dark brown spots may also appear on the petioles (leaf stems).
3. As the disease spreads, both the affected leaves and petioles can dry out and wither.

Control

1. The most effective way to manage anthracnose is through proper plant care and hygiene.
2. Make sure hydrangeas are spaced far enough apart to allow good air circulation.
3. Keep the area around the plants clean and free of fallen leaves or debris.
4. Always prune using sharp, disinfected tools to avoid spreading infection.
5. If the disease appears, treat the plant with a fungicide that contains thiophanate-methyl, which works well against anthracnose.

Botrytis Cinerea (Leaf Blight)

Botrytis cinerea, commonly known as gray mold, is a fungal disease that primarily attacks young plant tissues. It is often seen in crops like grapes and strawberries, but young hydrangea leaves and petioles are also vulnerable.

Symptoms

1. Early signs include black spots on the leaves, often with a gray, fuzzy mold appearing in the center.
2. When the infection spreads to the petioles, they turn pale brown, causing the affected leaves and stems to wither and fall off.

Control

1. Make sure hydrangeas receive enough sunlight and are not planted in overly shaded areas.
2. Provide ample spacing between plants to improve air circulation.
3. Keep the area around the plants clean and free of fallen or decaying leaves.
4. Water in the morning, so leaves have time to dry during the day.
5. Always water at the base of the plant, avoiding overhead watering.
6. If infection occurs, apply a fungicide designed to control gray mold (Botrytis cinerea) for effective treatment.

Powdery mildew (White fungus)

Powdery mildew is a distinctive fungal disease easily recognized by its white, powder-like coating on leaves. Unlike many other fungal infections, it can spread over long distances through wind or insects, and within a plant, it can be transmitted by raindrops or watering.

Symptoms

1. The most visible symptom is a white, dusty layer covering the leaf surface.
2. As the infection progresses, dark spots form beneath the coating, eventually causing the leaves to brown, wither, and die.

Control

1. Keep the garden clean and free of fallen leaves and plant debris.
2. Space hydrangeas properly to ensure good airflow and reduce humidity between plants.
3. Avoid overwatering, as excess moisture promotes fungal growth.
4. Stop fertilizing in late summer, particularly with high-nitrogen fertilizers, which encourage tender growth that’s more susceptible to infection.
5. Use Neem oil, a natural and eco-friendly treatment, to help control the disease.
6. For severe cases, apply fungicides containing sulfur or a systemic fungicide formulated to combat powdery mildew.

Rust (Pucciniastrum Hydrangeae)

Rust in hydrangeas, while similar to other rust diseases, has a unique lifecycle that requires two different hosts. It primarily affects Smooth hydrangea (Hydrangea arborescens) and occasionally Panicled hydrangea (Hydrangea paniculata). The secondary hosts are hemlock species such as Tsuga canadensis and Tsuga caroliniana.

Symptoms

1. The first signs of infection are pale yellow spots on the upper sides of the leaves, which gradually turn reddish-brown.
2. As the disease progresses, the affected leaves become yellow and eventually fall off.

Control

1. Keep the soil around hydrangeas moderately moist, avoiding excessive watering.
2. Provide good air circulation between plants to reduce humidity.
3. Avoid planting hydrangeas in deep shade.
4. Regularly clean the area around the plants, removing fallen leaves and dead plant material.
5. Choose rust-resistant hydrangea varieties when possible.
6. Remove and destroy infected leaves by discarding or burning them.
7. For chemical control, fungicides such as Chlorothalonil 720 SC or Daconil Weatherstik are effective options.

Verticillium Wilt

 Verticillium wilt is a serious fungal disease that can be deadly to many plants, though it rarely affects hydrangeas.

Symptoms

1. The disease causes leaves to turn yellow, wilt, and eventually fall off.
2. Brown streaks may appear on the stems.
3. In many cases, only part of the plant is affected while the rest remains healthy.

Control

1. Proper planting techniques and regular maintenance help reduce the risk of Verticillium wilt.
2. To prevent infection, treating the soil around the plant with chloropicrin can help minimize soilborne pathogens.
3. If symptoms appear, prune and remove the infected parts of the plant using clean, sterilized tools.
4. Applying fertilizers rich in phosphorus can also strengthen the plant and improve recovery.

Bacterial wilt (Ralstonia solanacearum)

Bacterial wilt is a serious plant disease that can be fatal, though it spreads less easily than fungal infections. The bacteria responsible are usually present in contaminated soil and can enter plants through their roots.
It can also spread between plants via unsterilized tools or contaminated water.

Symptoms

1. The first signs are wilting leaves.
2. Inside the stems, brown, decaying tissue develops.
3. As the disease progresses, the sap flow becomes blocked, causing further yellowing and wilting of the leaves.

Control

1. Buy plants only from trusted nurseries that ensure disease-free stock.
2. Always disinfect pruning tools before and after use.
3. Use clean, high-quality soil for planting and propagation to prevent introducing bacteria into the growing environment.

Bacterial Leaf Spot (Xanthomonas campestris)

The bacteria responsible for this disease cannot survive long outside a living plant, so soil transmission is relatively rare. However, they can easily spread from one plant to another through unsterilized tools used during pruning or propagation.

Symptoms

1. Small, water-soaked spots appear on the leaves and gradually enlarge, changing from pale green to darker shades.
2. In severe cases, the plant may lose a large portion of its foliage.

Control

1. Choose only healthy plants, especially when purchasing from nurseries, since that’s where most infections originate.
2. Avoid watering the leaves directly—water at the base instead.
3. Keep the garden free of fallen leaves and debris.
4. Always use clean, disinfected tools for pruning or propagation.
5. Avoid handling plants right after watering, when surfaces are still wet.
6. While certain fungicides can help limit the disease’s spread, complete elimination from an infected plant is not possible.

Hydrangea Ringspot Virus

This systemic disease moves through the plant’s sap but is not transmitted by insects or through seed propagation. The most common way it spreads is during the propagation of cuttings in nurseries, where symptoms often take time to appear.

Symptoms

The main sign of infection is the appearance of yellow, chlorophyll-free rings or oval spots on otherwise green leaves.

Control

1. Always choose healthy hydrangea plants from reliable sources.
2. Use clean, disinfected tools for pruning and general care.
3. If a plant shows signs of infection, it should be removed and destroyed.
4. After removal, disinfect the soil in which it grew and avoid replanting in that location for several years to prevent reinfection.

Hydrangea Mosaic Virus

This virus is similar to the one previously described, as it is not transmitted by insects or seeds. Infection usually occurs during vegetative propagation or after pruning with contaminated tools.

The disease mainly causes slower growth, and the leaves of infected plants are often smaller than normal.

Symptoms

Hydrangea leaves develop yellow patterns that vary in shape and size.

Control

1. Take cuttings only from healthy plants, using sterilized knives or pruning shears.
2. Destroy any plants showing signs of infection to prevent the virus from spreading further.

Impatiens necrotic spot virus (INSV)

INSV (Impatiens Necrotic Spot Virus) is a viral disease transmitted by insects, with thrips serving as the main carriers. If left uncontrolled, the infection can eventually kill the plant.

Symptoms

1. Dark rings with even darker centers appear on the leaves or stems.
2. As the disease advances, these rings often develop necrotic (dead) tissue.

Control

1. Eliminate the insect carriers, especially thrips, to prevent the virus from spreading.
2. At the first signs of infection, remove and destroy all affected plants immediately to stop further transmission.

Chlorosis

Chlorosis in plants can result from several factors, most commonly an iron deficiency in the soil. Other possible causes include root rot or imbalanced nitrogen levels.

Symptoms

1. The veins of the leaves remain green, while the areas between them turn yellow.
2. In more severe cases, the entire leaf may become yellow.

Control

1. If iron deficiency is the cause, enrich the soil with iron supplements.
2. When excess moisture is to blame, improve drainage to allow the soil to dry properly.
3. Also, maintain the correct mineral balance and soil pH to support the plant’s overall health and nutrient uptake.

Virescence

Virescence in hydrangeas occurs when other diseases disrupt the plant’s normal biological processes, causing abnormal growth and coloration. In severe cases, it can eventually kill the plant.

Symptoms

1. The most noticeable sign is when the flowers begin turning green as they start producing chlorophyll.
2. In some instances, small green leaves may also develop directly on the flower clusters.

Control

1. Focus on maintaining strong, healthy plants to reduce susceptibility.
2. Apply fungicides and pesticides regularly—ideally several times per season—as a preventive measure.
3. Provide proper fertilization and consistent watering to keep the plants vigorous and resilient against stress and disease.

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