Hydrangeas are strong and beautiful plants, but in the process of growing them can appear many problems. One such problem is various diseases. Unfortunately, hydrangeas have a wide list of threats that can harm them.
The most common are fungal diseases that mainly affect the leaves. The next threat is bacteria which are a serious problem for gardeners. Another nasty enemy is viruses. This is a separate group of microorganisms that are useless to fight. And finally, the disease is caused by anatomical changes or lack of trace elements in the soil. All of this will be discussed in this article.
|Name of disease (pathogen)||Symptoms||Management|
|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 is perhaps the most common disease of hydrangea. It usually does not destroy the plant, but young plants are at greatest risk.
Spores of this fungus overwinter in fallen leaves and earth. With the advent of the warm season, plants become infected. Most often, spores get on the plant with the help of wind or water drops (rain or watering) that throw them on the leaves.
Usually, everything happens in the summer, but the results of the fungus begin to become noticeable only in the fall. First, the spores settle on the lower leaves and then migrate higher.
Below is a list of hydrangea species that can be affected by this disease.
- Smooth hydrangea (Hydrangea arborescens)
- Panicled hydrangea (Hydrangea paniculata)
- Oakleaf hydrangea (Hydrangea quercifolia)
- Mophead Hydrangea (Hydrangea macrophylla)
- Hydrangea chinensis
The first signs of this disease are spots. Their shape is mostly circular, but on different species of hydrangeas, the spots can change and become rectangular.
The size of the spots is a quarter of an inch or less. Over time, the spots increase and may merge, and they also acquire an irregular shape.
The color of the spots is mostly brown, on different species and under different conditions, the color may be different shades of brown. Sometimes the color can be black or purple.
As a result, the leaves become very unaesthetic. Also, with a large number of spots, the leaves turn yellow and fall off after a while.
The first thing to do to avoid infection is to plant a hydrangea properly. The plant should have enough space around it so that the air circulates freely, and the leaves do not stay wet for a long time. Plants also need partial shade because, in such conditions, it is easier to fight the disease.
Next is proper watering, do not water the plants on top of the leaves (overhead). It is best to water the plant on the surface around the crown; you can also arrange drip irrigation. Another mistake is excessive watering, avoid it. Hydrangeas love moist soil, but excess water can harm them.
When pruning a hydrangea, use sterile instruments. Also, several times a year, clean the area around the plant from fallen leaves and other debris. Do not leave them to rot in your yard, and it is better to throw them as far as possible.
If the infection has already occurred and you see visible signs of this disease, then tear off all the damaged leaves and throw them in the trash.
Spray the plant with an aqueous solution of fungicide. Products containing chlorothalonil or thiophanate-methyl are best suited for this purpose. Strictly follow the recommendations on the label.
Since the signs of the disease may become noticeable only at the end of the season, it is recommended to spray the plants in late spring for prevention.
Anthracnose is another common disease that affects not only hydrangeas but also many other plants. It is unlikely that the plant will die as a result of this disease, but the appearance will be severely damaged.
As in the previous case, the spores of the fungus overwinter on the surface of the earth in plant remains. Also, spores can penetrate the buds or internodes and comfortably survive the winter there.
When spring comes and the weather becomes favorable, the wind and rain spread the spores throughout the garden, and they settle on the leaves of plants. Unlike Cercospora, this disease does not require warm weather. On the contrary, it is more comfortable in cool climates but with high humidity. So if the spring is dry, the risk of infection is reduced and vice versa.
The results of the disease can be seen in the summer. On plants, there are spots of different sizes and shapes. The color can be different, but mostly it is brown spots of irregular shape that expand quite quickly.
Anthracnose can also affect young hydrangea stems. Petioles are covered with black or dark brown spots and eventually wither with the leaves.
However, most often, the spots cover a large part of the leaf, and it turns yellow; after a short time, the leaves fall off.
It also happens that the hydrangea is affected by several diseases at the same time. In the picture, you can see the plant affected by Anthracnose and Cercospora.
Control methods include proper care, namely planting and watering. As in the previous case, do not thicken your hydrangeas, give them enough space.
The bushes should always be clean. If you have mulched your plants, make sure you use only quality material for this.
Pruning should be done with clean and sharp tools. After pruning, spray the wounds with a solution of fungicide.
Thiophanate-methyl products work most effectively against Anthracnose. This is a systemic fungicide that penetrates the plant and acts from the inside. Prophylactic spraying in the spring is most desirable, as it can prevent a wide range of diseases, including Cercospora.
Botrytis Cinerea (Leaf Blight)
Botrytis Cinerea – another name – gray mold, affects mostly young parts of the plant. Very common on grapes and strawberries. Unfortunately, young leaves and petioles of hydrangeas can also fall victim to this scourge.
Spores of this fungus can persist in the soil for several years. They are not afraid of frost or other adverse weather conditions.
When the air temperature approaches 70 ° F (21 ° C), spores begin to develop on the plants. The best conditions for the disease are cloudy and rainy weather.
Most often, the fungus develops on young succulent leaves and petioles. The disease can cause serious damage to the plant.
The symptoms are spots on the leaf; at first, they are small and then develop and capture more and more of the leaf. Their color can be different, but most often, they are black. In the later stages of the disease in the center of the spot, you can see gray mold.
If the disease has spread to the petioles, they also change color and become pale brown. As a result, they wither and fall off together with the leaves.
This disease most often develops in the shade, so avoid too much shading of the hydrangea. Plants should also have free space around them so that the wind dries the leaves after the rain.
The surface around the plant should be clean, do not let the leaves rot near the plants. Organic fertilization with quality compost also gives a good result. After feeding, the plants become more resistant to infection.
Water the hydrangeas only in the morning so that the sun dries the leaves and stems. Also, try to water the plant close to the ground, avoid overhead watering. Otherwise, you will create ideal conditions for the development of the disease.
If an infection has occurred, remove the affected parts of the plant and throw them away from the yard or burn. Then spray the plants with a fungicide. There are products on the market that are designed to combat this disease. You can also buy organic fungicides that cope well with Botrytis Cinerea and do not contain chemicals.
Powdery mildew (White fungus)
Powdery mildew is markedly different from other fungal diseases due to its white color. This disease is spread by insects or wind over long distances. On a plant, migration also occurs by rain or watering.
The most common lesion occurs on young succulent leaves and other parts, such as leaf stalks. Mature leaves are more resistant to this disease.
The best weather for the development of the disease is dryness and warm temperature. This fungus, unlike others, does not require high humidity. The results of the infection become noticeable in late summer.
You can’t go wrong when you see the leaves affected by Powdery mildew because it is covered with a white coating that is difficult to confuse with anything else. New fungal spores develop in this white powder, and next year they will spread and settle on new hosts.
At serious infection, under a white coating, there are dark spots as a result of leaves brown and dies.
To reduce the spread of the disease, you need to follow the recommendations as in previous cases. That is, keep the environment in the garden clean and free of rotten leaves and plant debris. You should plant hydrangeas at a sufficient distance from each other. Do not water the plants with too much water.
Another important recommendation – you should not feed the plants in the second half of summer, especially do not use fertilizers with high nitrogen content. The fact is that such fertilizers can cause the growth of young leaves. The disease is most active in mid-summer, and if at this time begin to form young leaves and shoots, they will be infected.
Spraying plants with milk gives good results in the fight against this disease. You can also beat Powdery mildew with Neem Oil, which is also an organic product that is safe for the environment.
In addition, there are chemical control methods, for example, the use of sulfur or systemic fungicides. They are also effective, but to use them, you need to understand how to work with them and follow all the manufacturer’s recommendations.
Rust (Pucciniastrum Hydrangeae)
Rust on hydrangeas has its differences, but like other similar diseases requires two hosts. Among hydrangeas, rust parasitizes on Smooth hydrangea (Hydrangea arborescens). Sometimes this disease affects Panicled hydrangea (Hydrangea paniculata). The second type of host is hemlock (Tsuga canadensis or Tsuga caroliniana).
The disease winters on one host and, in the warm season, migrate to another.
Luckily rust rarely destroys the plant, mostly it all ends with cosmetic damage. However, if the plants are young or you have not noticed the disease in time, then the damage can be significant.
The problem is that the main part of the body of the fungus develops on the lower part of the leaf, so it is difficult to notice the disease at an early stage. On the upper part of the leaf, you can notice only pale yellow spots that only eventually become reddish-brown.
In the later stages, the leaves turn yellow and fall off.
To prevent the disease, follow all the recommendations and proper cultivation of hydrangeas, namely:
- the soil should not be too moist around the plants,
- the air should move freely between the plants,
- do not plant hydrangeas in full shade,
- clean the whole garden of fallen leaves and dead parts of plants.
There is one variety of hydrangea that is resistant to this disease its name Smooth hydrangea ‘Frosty.’ Also, do not plant Smooth hydrangeas if hemlock grows nearby.
Cut off all infected leaves and throw them away or burn them.
You can use chemical control methods, namely Chlorothalonil 720 SC or Daconil Weatherstik. These fungicides are designed to combat this disease. Follow the instructions on the label!
Verticillium Wilt is a very serious disease that can kill a plant, although it rarely affects hydrangeas.
It all starts under the ground. Under favorable conditions, the spores of the fungus penetrate into the roots, and the disease begins to develop in plant tissues.
Spores can remain in the ground for many years undamaged.
As a result of the disease in the plant stops the movement of water to the leaves and petioles. External signs may be different; the leaves may turn yellow or wither and then fall off. Brown marks may also be visible on the stem.
The disease often affects only part of the plant, and the other part may look undamaged.
It is difficult to control this disease. There are almost no chemical methods. Proper planting and care of hydrangeas reduce the risk of infection.
To prevent disease, you can treat the ground around the bush with chloropicrin. This product greatly reduces the number of pathogens in the soil.
When the plant is diseased, remove the affected parts with sterile pruning shears. Also, a positive result can be achieved using fertilizers that contain a lot of phosphorus.
If the disease has developed too much, the plant should be dug up and destroyed.
Bacterial wilt (Ralstonia solanacearum)
Bacterial wilt is a fairly severe disease that can lead to plant death. Fortunately, it does not spread as easily as fungal spores. Most often, the infection occurs through the soil that contains the pathogens of this disease.
You can also spread the disease to other plants with non-sterile instruments or watering. Whether the disease is transmitted by insects is not yet known.
The disease enters the plant through wounds. When the air temperature rises above 68 ° F (20 ° C), it begins to progress.
The most noticeable sign is the withering of the leaves. Sometimes only part of the leaf may wither. In other cases, all the leaves wither on one or more branches, and the rest of the plant remains healthy in appearance.
Infected stems look healthy, but if you cut them lengthwise or crosswise, you may notice brown (rotten) tissue inside. As a result, the sap flow on the stem deteriorates, and the leaves turn yellow and wither.
The first thing you need to do is try to avoid this disease. Therefore, buy only healthy quality plants from reliable nurseries.
Use only sterile tools when pruning.
When planting or propagating, use only quality sterile soil.
There are no chemicals that can cure the plant yet. Therefore, if your hydrangea has this disease, you need to remove the plant from the yard to avoid the spread it.
Bacterial Leaf Spot (Xanthomonas campestris)
Pathogens of this disease can not stay alive outside the plant for a long time, so infection through the soil is quite rare.
There have been cases of infection of the following types of hydrangeas:
- Smooth hydrangea (Hydrangea arborescens)
- Oakleaf hydrangea (Hydrangea quercifolia)
- Mophead Hydrangea (Hydrangea macrophylla)
Bacteria often spread from plant to plant through non-sterile instruments during pruning or propagation. Spreading can also occur if the plants are placed too close, and during watering or rain, the droplets transfer bacteria from the infected plants to the healthy ones.
At first, there are no signs of the disease. After some time on the surface of the foliage appear small spots that emit moisture. Then they become larger, and their color changes to pale green, later they darken. As a result, the plant may lose much of its foliage.
Choose only healthy quality plants. Most often, the spread occurs in nurseries.
Do not water the plants on top of the foliage. Clean the garden from fallen leaves and branches. Use clean tools. Do not work with plants immediately after watering.
There is evidence that some fungicides can suppress the disease, but it is impossible to cure the plant. Therefore, if you have this problem, you need to get rid of the infected plant as soon as possible.
Hydrangea Ringspot Virus
It is a systemic disease that is spread by a sap in the plant. Scientists claim that insects do not spread it. Also, the transmission of the disease is impossible due to seed propagation.
Most often, the spread occurs in nurseries during propagation by cuttings. The disease does not manifest itself immediately.
Signs are yellow chlorophyll-free circles on green leaves. The shape of the circles can be oval.
There are no effective methods to deal with this virus. First of all, when buying, choose only healthy hydrangeas. When pruning or doing other garden work, use a clean and disinfected tool.
In case of infection, the plant must be destroyed. Then disinfect the ground where it grew and do not plant anything in this place for several years.
Hydrangea Mosaic Virus
This virus is very similar to the previous one, and it is also not transmitted by insects or seeds. Usually, the infection occurs during vegetative propagation or after pruning.
The result of the disease is a slowdown in growth, and the leaves also become slightly smaller.
Signs of the disease are yellow patterns on the leaves of hydrangeas. Their shape and size can vary.
The only way to do anything is to reduce the spread of the virus. Cuttings should be taken only from healthy plants, and a sterile knife or pruning shears should be used. All infected plants must be destroyed.
Impatiens necrotic spot virus (INSV)
INSV is spread by insects. The main vectors of the disease are thrips.
Over time, the disease develops, and the plant dies.
Signs of infection are dark rings with a dark middle; over time, the rings may develop necrosis.
There are two ways to deal with this, the first is to destroy vectors (insects), and the second is to destroy all plants at the first sign of infection.
Various factors can cause chlorosis. Most often, it is a lack of iron in the soil, and the second reason may be root rot. The wrong amount of nitrogen can also cause chlorosis.
Some research is needed to pinpoint the causes.
The leaves turn yellow; usually, the veins remain green, and only the areas between them turn yellow. Sometimes the leaf may turn yellow completely. As a result, the plant produces little chlorophyll and becomes weak. I wrote an article on the subject of hydrangea leaf yellowing, which you can find by following this link.
Depending on what caused the disease, treatment will be different. If there is not enough iron, then you need to add this element to the soil. If there is excess moisture, you need to arrange drainage. Also, maintain the right balance of minerals in the soil.
The causes of Virescence are other diseases that cause changes in the plant. With severe infection, the hydrangea may die.
The flowers turn green, and they begin to produce chlorophyll. Also, small green leaves are formed on the flowers.
Grow only healthy plants. Several times a season, spray hydrangeas with fungicides and pesticides for prevention. Fertilize and water the plants.