Although the hydrangea is one of the robust and resistant plants, this garden beauty is not immune to diseases. If the attractive hydrangea loses its flowers or suffers from discoloration of the leaves, care errors are rarely the cause. Fungi and other diseases can be very damaging to the hydrangea, so quick action is required.
What diseases can affect hydrangeas and how do you fight them?
Hydrangeas can suffer from fungal diseases such as downy and powdery mildew, leaf spot fungi and Botrytis bud rot. Deficiencies or care errors can lead to chlorosis. Countermeasures include removing infected plant parts, using fungicides, checking nutrient supply and applying suitable hydrangea fertilizer.
Fungal diseases
In certain weather conditions, fungi thrive excellently and can attack numerous hydrangeas and other plants within a very short period of time. In this case, it is important to react quickly to prevent massive damage to the hydrangea. Below are the most common mushrooms:
Downy mildew
This fungus causes probably the most stubborn hydrangea disease. It often occurs in connection with warm and relatively dry weather conditions. The whitish-gray fungal growth appears on the underside of the leaves and is therefore often overlooked in the early stages of the disease. On the upper side of the leaf you can initially see yellowish, later clear red spots, which are similar to the damage caused by other leaf spot fungi. In an 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 mushroom is immediately recognizable even to the layperson thanks to its flour-like, dusty coating. The powdery mildew fungus is easy to wipe off and only affects the top side of the leaves. As the stage progresses, the leaves curl up and show necrosis. The plant begins to worry, and if the infestation is severe, it partially dies.
Combating mildew
Mildew must be combated consistently to prevent the disease from spreading:
- Remove affected plant parts and dispose of them in household waste. This prevents the fungal spores from spreading further.
- Spray hydrangea with horsetail broth, garlic broth or tansy.
- The microorganisms contained in milk or whey support you in combating powdery mildew and help the plant build up resistance. The affected areas must be treated several times with diluted milk or whey.
- Beneficial insects such as ladybirds or sawflies keep the fungus in check. Therefore, only use fungicides and insecticides in the garden that protect these animals.
- When there is a severe infestation, the only option is often the chemical treatment. When applying the fungicides, strictly adhere to the dosage stated on the packaging.
Leaf spot fungi
With this fungal disease, the leaves turn yellowish and brown spots of different sizes form. The discolored leaf tissue thins out and is ultimately rejected by the plant. In addition to high humidity, the causes of leaf spot fungi are in many cases a poor supply of nutrients.
Control measures
- Remove all affected leaves and dispose of them in household waste. Fallen leaves must also be consistently picked up and destroyed to prevent new infection.
- Tighten hydrangea regularly so that the leaves can dry quickly.
- Check the supply status of the hydrangea and fertilize if necessary.
- If the hydrangea is severely infested, spray it 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 is not ventilated infrequently in the house during the winter.
Prevention and control
- Overwinter the hydrangea in a cool room, ventilate at least once a day.
- Check humidity regularly.
- Cut off affected plant parts.
- If the infestation is severe, treat hydrangea with a fungicide.
Illnesses as a result of care errors or deficiency symptoms
Diseases caused by incorrect cultivation conditions can usually be combated without any problems and the hydrangea recovers quickly.
Chlorosis
In this disease, the foliage yellows from the tip and turns brown in the later stages. If this damage occurs on the older leaves, the hydrangea is lacking potassium, magnesium, nitrogen and, in rare cases, phosphorus. However, if the leaf damage is visible on freshly sprouted leaves, the hydrangea usually lacks iron. Less commonly, a lack of copper or zinc is responsible for chlorosis.
Iron deficiency often occurs when there is an excess of lime in the soil. That is why pink or red colored hydrangeas are more often affected by this disease. They depend on a soil pH value of over 6 to express their flower color. In order to change slightly acidic soils into the alkaline range, lime must be applied frequently and the hydrangea can no longer absorb enough iron.
Remedy
- To be sure which nutrients the hydrangea is missing, a soil analysis is recommended.
- Acidify overly limed soils with leaf compost, peat or rhododendron soil.
- If there is iron deficiency, give ferramin foliar fertilizer (€6.00 on Amazon).
- Fertilize in the future with special hydrangea fertilizer with iron content.
Tips & Tricks
If the hydrangea grows very poorly and forms small inflorescences, it is suffering from hydrangea virosis. Unfortunately, this disease caused by mycoplasma or viruses cannot be treated and prevention is also not possible. The plant must be disposed of and you must not plant any other hydrangeas in the same place.
