Hydrangeas, known for their robust beauty, often encounter several issues during their growth. Among these, a range of diseases poses significant threats to their well-being. These plants are susceptible to a diverse array of health challenges that can impact their growth and appearance.
|Cercospora (Cercospora hydrangeae)||Brown spots||Remove infected leaves, spray with a fungicide|
|Anthracnose ( Colletotrichum gloeosporioides, Colletotrichum dematium)||Red-brown spots on leaves||Prophylactic spraying with fungicides|
|Botrytis Cinerea (Botryotinia fuckeliana)||Black spots in grey molid in center||Avoid planting in too shade places, use biological fungicides|
|Powdery mildew (Erysiphe friesii var. friesii)||White coating on leaves||Neem Oil, fungicides|
|Rust (Pucciniastrum Hydrangeae)||Red spots on leaves||Remove affected leaves, spraying with fungicide|
|Verticillium Wilt (Verticillium dahliae, V. albo-atrum)||Leaves turn yellow and wither||Remove affected leaves and branches, use a high-phosphorus fertilizer|
|Bacterial wilt (Ralstonia solanacearum)||Leaves wither||Buy healthy plants, use clean soil|
|Bacterial leaf spot (Xanthomonas campestris)||Small spots on leaves that emit moisture||It is impossible to cure, buy healthy plants, remove infected ones.|
|Hydrangea ringspot virus (HRSV)||Yellow circles on leaves||Plant only healthy hydrangeas, remove infected|
|Hydrangea mosaic virus (HydMV)||Yellow patterns on leaves||Cuttings should be taken only from healthy plants|
|Impatiens necrotic spot virus (INSV)||Circles on leaves||Destroy vectors of disease|
|Chlorosis||Leaves turn yellow||Add iron to the soil, create drainage|
|Virescence||Flowers become green||Spray with remedies to prevent all diseases.|
Cercospora Leaf Spot
Cercospora, a common hydrangea disease, generally doesn’t kill the plant, but it’s particularly risky for young hydrangeas.
The fungus responsible for this disease survives winter in fallen leaves and soil. As temperatures rise, the spores infect plants, often spread through wind or water droplets from rain or irrigation, landing on the leaves.
Infection typically occurs in summer, but signs of the fungus are usually only visible by fall. Initially, the spores affect the lower leaves before moving upwards.
- The initial symptom is the appearance of small spots, each less than a quarter-inch in diameter.
- These spots are mainly brown, but their shade can vary depending on the hydrangea variety and environmental conditions.
- A high number of spots can cause leaves to turn yellow and eventually drop off.
- To prevent infection, proper planting is crucial. Ensure adequate space around each hydrangea for free air circulation and to prevent leaves from remaining damp.
- Proper watering is key; avoid overhead watering and excessive moisture.
- Use sterilized tools for pruning hydrangeas.
- Regularly clean the area around the plant, removing fallen leaves and debris.
- If infection occurs and signs are evident, remove and dispose of all affected leaves.
- Treat the plant with a fungicide solution, preferably containing chlorothalonil or thiophanate-methyl, adhering to label instructions.
Anthracnose is a prevalent disease that affects hydrangeas and various other plants. While it’s unlikely to kill the plant, it can significantly mar its appearance.
As spring arrives and conditions become more conducive, wind and rain help disperse the spores throughout the garden, where they settle on plant leaves.
The disease presents as spots of varying sizes and shapes on the leaves.
Anthracnose can also impact the young stems of hydrangeas. The petioles may develop black or dark brown spots and, along with the leaves, eventually wither.
- Effective control methods focus on proper plant care, including planting and watering techniques.
- Ensure hydrangeas are not planted too closely together; they need sufficient space.
- Maintain cleanliness around the bushes. If using mulch, opt for high-quality materials.
- Prune with clean, sharp tools. After pruning, treat the cuts with a fungicide solution.
- For combating Anthracnose, products containing thiophanate-methyl are highly effective.
Botrytis Cinerea (Leaf Blight)
Botrytis Cinerea, also known as gray mold, predominantly targets the younger parts of plants and is especially common in grapes and strawberries. Young hydrangea leaves and petioles are also susceptible to this affliction.
The spores begin to develop when air temperatures reach around 70 °F (21 °C), with cloudy and rainy weather creating ideal conditions for the disease.
- The disease manifests as black spots on the leaves, with gray mold visible at the center of these spots.
- If the disease spreads to the petioles, they change to a pale brown color, leading to their withering and eventual detachment along with the leaves.
- Ensure the hydrangea isn’t overly shaded.
- Allow sufficient space around the plants for wind circulation to help dry the leaves after rainfall.
- Keep the ground around the plant clear and free from rotting leaves.
- Water hydrangeas in the morning, allowing the sun to dry the leaves and stems. Water at the base to avoid overhead watering.
- If infection occurs, remove and dispose of the affected plant parts.
- Treat the plants with a fungicide specifically formulated to combat Botrytis Cinerea.
- Organic fungicides, effective against Botrytis Cinerea and free from harsh chemicals, are also available as an alternative.
Powdery mildew (White fungus)
Powdery mildew, distinct in its white appearance, differs from other fungal diseases. It spreads over long distances through insects or wind, and within a plant, it can be transmitted by rain or watering.
This disease most commonly affects young, succulent leaves and other parts like leaf stalks, while mature leaves show greater resistance.
- The leaves exhibit a white powdery coating.
- Beneath this coating, dark spots develop, leading to the browning and eventual death of the leaves.
- Maintain a clean garden environment, free from decaying leaves and plant debris.
- Plant hydrangeas with adequate spacing to prevent overcrowding.
- Avoid overwatering the plants.
- Refrain from feeding plants in the latter half of the summer, especially avoiding high-nitrogen fertilizers.
- Neem Oil, an organic and environmentally friendly product, is effective against Powdery mildew.
- Chemical control options, such as sulfur or systemic fungicides, are also available for managing this disease.
Rust (Pucciniastrum Hydrangeae)
Rust in hydrangeas, while sharing similarities with other rust diseases, requires two hosts for its lifecycle. It primarily targets Smooth hydrangea (Hydrangea arborescens) and occasionally Panicled hydrangea (Hydrangea paniculata). The secondary hosts are species of hemlock (Tsuga canadensis or Tsuga caroliniana).
Fortunately, rust typically causes only cosmetic damage to hydrangeas and rarely leads to plant death. However, significant harm can occur if the plants are young or the disease is not identified early.
- Initially, pale yellow spots appear on the upper side of the leaves, which eventually turn reddish-brown.
- Affected leaves turn yellow and fall off.
- Ensure the soil around the plants is not excessively moist.
- Promote free air circulation between plants.
- Avoid planting hydrangeas in fully shaded areas.
- Regularly clean the garden of fallen leaves and dead plant material.
- There is a hydrangea variety resistant to this rust disease.
- Remove and dispose of all infected leaves, either by throwing them away or burning them.
- For chemical control, products like Chlorothalonil 720 SC or Daconil Weatherstik can be effective.
Verticillium Wilt is a severe disease that can be lethal to plants, though it infrequently affects hydrangeas.
The disease originates underground. Under conducive conditions, fungal spores infiltrate the roots, initiating the disease’s progression within the plant’s tissues.
- Leaves may yellow, wilt, and eventually fall off.
- Brown streaks might also appear on the stem.
- Often, the disease impacts only a portion of the plant, leaving the rest appearing healthy.
- Correct planting and maintenance practices can lower the risk of Verticillium Wilt in hydrangeas.
- To prevent the disease, treating the soil around the bush with chloropicrin can significantly reduce soilborne pathogens.
- If the plant is infected, remove the diseased parts using sterile pruning tools.
- Applying phosphorus-rich fertilizers can also contribute to a positive outcome in managing this disease.
Bacterial wilt (Ralstonia solanacearum)
Bacterial wilt is a serious disease that can be fatal to plants. Thankfully, it doesn’t spread as readily as fungal diseases. Infection typically occurs through soil harboring the bacterial pathogens.
The disease can also be transmitted to other plants through the use of non-sterile tools or contaminated water.
Bacterial wilt enters the plant via wounds and intensifies when air temperatures exceed 68 °F (20 °C).
- The leaves begin to wilt.
- The stems show brown, rotten tissue internally.
- Impaired sap flow in the stems, leading to leaf yellowing and wilting.
- Purchase plants only from reputable nurseries that guarantee their health.
- Always use sterilized tools for pruning.
- For planting and propagation, utilize high-quality, sterile soil.
Bacterial Leaf Spot (Xanthomonas campestris)
The pathogens causing this disease struggle to survive outside a plant for extended periods, making soil transmission relatively uncommon.
However, bacteria can readily spread from plant to plant through the use of non-sterile tools during pruning or propagation. Additionally, if plants are situated too closely, water droplets from irrigation or rain can transfer bacteria from infected to healthy plants.
- Small, moist spots appear on the foliage, which enlarge and change from pale green to a darker hue.
- The plant may lose a significant portion of its foliage.
- Select only healthy plants, particularly from nurseries, where most disease spread occurs.
- Avoid watering the foliage directly.
- Keep the garden clear of fallen leaves and branches.
- Always use clean tools.
- Avoid working with plants immediately after watering.
- Some fungicides may help control the disease, but complete eradication in an infected plant is not possible.
Hydrangea Ringspot Virus
This systemic disease spreads through the sap within the plant. Research indicates that insects do not facilitate its transmission, and seed propagation does not spread the disease either.
The most common avenue for spread is in nurseries during the propagation of cuttings, and symptoms do not appear immediately.
- The primary indicator is the presence of yellow, chlorophyll-free circles on green leaves, which may be oval in shape.
- Ensure you select healthy hydrangeas.
- Use clean and disinfected tools for pruning and other gardening activities.
- If infection is detected, the plant should be destroyed. Afterwards, disinfect the soil where it was growing and avoid planting in that spot for several years.
Hydrangea Mosaic Virus
This virus shares similarities with the previously mentioned one, including its non-transmission by insects or seeds. Infection typically occurs during vegetative propagation or following pruning.
The disease primarily causes a slowdown in growth, and affected leaves may also be smaller than usual.
Hydrangea leaves develop yellow patterns, which can vary in shape and size.
- Ensure that cuttings are taken only from healthy plants, using a sterile knife or pruning shears.
- All plants infected with the virus must be destroyed to prevent further spread.
Impatiens necrotic spot virus (INSV)
INSV (Impatiens Necrotic Spot Virus) is transmitted by insects, with thrips being the primary carriers. As the disease progresses, it can ultimately lead to the death of the plant.
- The presence of dark rings with a darker center on the plant.
- These rings may develop necrosis over time.
- Eradicate the insect vectors, particularly thrips, to prevent the spread of the disease.
- Upon the first indication of infection, all affected plants should be destroyed to halt further transmission.
Chlorosis in plants can arise from several causes, with the most common being iron deficiency in the soil. Other potential reasons include root rot and improper nitrogen levels.
- The leaf veins retain their green color while the areas between them turn yellow.
- In some cases, the entire leaf may become yellow.
- If chlorosis is due to iron deficiency, supplement the soil with iron.
- In cases of excess moisture, improving soil drainage is necessary.
- Additionally, ensure the soil has the correct balance of minerals and pH for optimal plant health.
Virescence in hydrangeas is triggered by other diseases that induce changes in the plant’s normal processes. In severe cases, this can lead to the plant’s demise.
- The flowers start turning green as they begin to produce chlorophyll.
- Additionally, small green leaves may form on the flowers.
- Prioritize growing healthy plants.
- Regularly, perhaps several times a season, apply fungicides and pesticides as preventive measures.
- Ensure proper fertilization and watering of the plants for their optimal health.