Overview of the diseases that occur in hydrangeas

Overview of the diseases that occur in hydrangeas

Fungal diseases

In certain weather conditions, mushrooms thrive and can attack numerous hydrangeas and other plants within a very short time. In this case, it is important to react quickly to prevent massive damage to the hydrangea. The following are the most common fungi:

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Wrong mildew

This fungus causes the most stubborn hydrangea disease. It occurs more frequently in connection with warm and relatively dry weather conditions. The whitish gray fungal lawn shows up on the underside of the leaf and is therefore often overlooked in the early stages of the disease. On the upper side of the leaf, yellowish, later distinct red spots can be seen, which resemble the damage caused by other leaf spot fungi. In the advanced stage, powdery mildew can also spread to the shoots, buds and flowers. If the infestation is severe, there is a risk that the hydrangea will die completely.

Powdery mildew

This bad weather fungus is instantly recognizable even for laypeople due to the powdery coating. The fungus lawn of powdery mildew can be easily wiped off and only affects the upper side of the leaf. As the stage progresses, the leaves curl up and show necrosis. The plant begins to worry, if it is heavily infested, it partially dies.

Control of powdery mildew

Powdery mildew must be controlled consistently to prevent the disease from spreading:

  • Remove infected parts of the plant and dispose of with household waste. This prevents the fungal spores from spreading further.
  • Sprinkle hydrangea with horsetail broth, garlic stock or tansy.
  • The microorganisms contained in milk or whey support you in fighting powdery mildew and help the plant to build up resistance. The affected areas must be treated several times with diluted milk or whey.
  • Beneficial organisms such as ladybugs or sawfly keep the fungus at bay. Therefore, only apply fungicides and insecticides in the garden that protect these animals.
  • In the case of severe infestation, often only the chemical club remains. When applying the fungicides, strictly adhere to the dosage indicated on the packaging.

Leaf spot fungi

With this fungal disease, the leaves turn yellow and brown spots of different sizes form. The discolored leaf tissue thins and is eventually rejected by the plant. In addition to high humidity, the causes of leaf spot fungus are in many cases a poor supply of nutrients.

Control measures

  • Remove all infected leaves and dispose of them with household waste. Even fallen leaves must be consistently collected and destroyed in order to prevent re-infection.
  • Thinning out hydrangea regularly so that the leaves can dry off quickly.
  • Check the supply status of the hydrangea and fertilize if necessary.
  • In the case of severe infestation, spray Hydrangea with a suitable fungicide.

Botrytis bud rot (gray mold)

You can recognize this disease by the light gray, downy coating that covers the buds. Gray mold is promoted by high humidity and occurs, for example, if the hydrangea in the house is not ventilated enough during the winter.

Prevention and control

  • Winterize the hydrangea in a cool room, ventilate it at least once a day.
  • Check humidity regularly.
  • Cut off infected parts of the plant.
  • If the infestation is severe, treat the hydrangea with a fungicide.

Illnesses as a result of care errors or deficiency symptoms

Diseases that are caused by incorrect culture conditions can usually be combated without any problems and the hydrangea recovers quickly.


In this disease, the leaves turn yellow from the top and turn brown in the later stages. If this damage occurs on the older leaves, the hydrangea lacks potassium, magnesium, nitrogen and, in rare cases, phosphorus. However, if the leaf damage shows on the freshly sprouted leaves, the hydrangea mostly lacks iron. Less often, a lack of copper or zinc is responsible for chlorosis.

Iron deficiency often occurs when there is excess lime in the soil. That is why pink or red colored hydrangeas are more often affected by this disease. They are dependent on a soil pH value of more than 6 in order to develop their flower color. In order to differentiate slightly acidic soils into the basic area, liming often has to be carried out and the hydrangea can no longer absorb enough iron.


  • To be sure which nutrients the hydrangea is missing, a soil analysis is recommended.
  • Acidify overcalcified soils with leaf compost, peat or rhododendron soil.
  • In case of iron deficiency, give Ferramine foliar fertilizers.
  • In future fertilize with a special hydrangea fertilizer with iron content.

Tips & Tricks

If the hydrangea grows very poorly and forms small inflorescences, it is infected with the hydrangea virus. Unfortunately, this disease caused by mycoplasma or viruses cannot be treated and prevention is not possible. The plant must be disposed of and you must not plant any other hydrangeas in the same place.