Garden design and maintenance

Recognize and treat hydrangeas diseases: this is how it works!

A profuse blooming hydrangea is a decorative element in any garden. Planting hydrangeas is not difficult, but their care is a little more demanding than other garden shrubs. Diseases and pests can also attack the plants and prevent their development. In this article we are going to take a closer look at the most common hydrangea diseases and their treatment and preventive measures.

How many species of hydrangea are there?

Hydrangea problems can have several causes

The hydrangea belongs to the hydrangea family (Hydrangeaceae) and is native to East Asia. There are over 80 types of hydrangeas, which can be roughly divided into 3 groups:

  • Forest hydrangea (Hydrangea arborescens)
  • Farmer’s hydrangeas (Hydrangea macrophylla)
  • Panicle hydrangea (Hydrangea paniculata)

They all differ in growth form, flower shape and color, but the hydrangea diseases and pests listed here are typical for all species. The causes are mostly metabolic disorders or fungi.

Hydrangea diseases that are caused by metabolic disorders

Hydrangea diseases that are caused by metabolic disorders

The hydrangea is a real eye-catcher in the garden, but caring for it is a bit tiring. The plant is quite demanding and there are certain factors to which it reacts extremely violently. Most often, leaf diseases are caused by:

  • too much sun
  • too much water
  • Lack of nutrients
  • Changes in the acidity of the soil

The leaves of the hydrangea are falling off

dry falling leaves of pink panicle hydrangea

Diseases and pests are not always the cause when hydrangeas lose leaves. If the leaves turn yellow or fall off, this is a sign of poor watering in hot weather and a lack of nutrients. Water more often and fertilize every 10 days with a special fertilizer for hydrangeas.

Brown spots on the leaf margin

black spots on the leaves of the hydrangea

If brown dry spots appear on the edge of the leaf that gradually cover the entire leaf, the causes may be hard water and sunburn. It is necessary to shade the plants and use water that is low in lime for watering. Let the water stand in the watering can for a few days so that the limescale settles on the can wall. Rainwater is also very suitable for watering.

The leaves turn dark green

Hydrangea leaves too much watered

Are the leaves of your hydrangea becoming soft, shapeless, and dark in color? This can occur from heavy soils, sudden increases in temperature, or excessive watering. The irritant should be removed or the plant should be transplanted.

hydrangea overwatering what to do

Yellow leaves on hydrangeas indicate chlorosis

When hydrangea turns yellow leaves

When hydrangeas get yellow leaves, they can suffer from chlorosis. The leaves of the diseased plant turn lighter and yellow, while the veins remain dark green. Sagging leaves and deformation of the buds can be observed. The main cause of the disease is a metabolic disorder of the plant – it has an iron deficiency or cannot absorb iron from the soil on its own. Chlorosis is most common when a shrub has grown in the same place for many years.

When hydrangea turns yellow leaves

Preparations such as anti-chlorosis, Optifer 6 or hw-ferrovit are used to treat iron deficiency in plants. It is possible to make iron fertilizer yourself:

  • 2 g of iron vitriol and 4 g of citric acid are diluted in 1 liter of water. The leaves are then treated with the solution.
  • Dissolve 40 g calcium nitrate in 12 liters of water (1 bucket). The plant is watered several times with the mixture. Then fertilization with an iron sulfate solution is repeated. The ratio of iron sulfate to water is similar.

Hydrangea diseases that are caused by fungi

Powdery mildew in hydrangea

Hydrangeas are not affected by fungal diseases very often. Fungal spores remain in the soil for a long time, but can cause serious damage under favorable weather conditions. The same fungal diseases are also common in peonies.

Gray mold rot (Botrytis cinerea)

Gray mold rot (Botrytis cinerea)

Damaged tissue becomes soft and watery. In hot weather, they dry out and depressions form on the plants, which the fungus eats away. The main factor in the development of the disease is rainy weather. The fungus spreads quickly and affects the entire shrub.

Gray mold rot Botrytis cinerea

The infected parts of the plant should be removed and burned, and the shrub should be sprayed with a fungicide from the benzimidazole group, such as thiabendazole or benomyl 50% Wp.

Downy mildew, downy mildew (lat.peronosporaceae)

Peronosporaceae fungus on the leaf

Moist air and temperatures of 18-20 degrees Celsius contribute to the development of the disease. Greasy spots form on the leaves that darken over time. The shrubs should be treated with the following solution: dissolve 150 g of soap flakes in 10 liters of water and add 15 g of copper sulfate.

Powdery mildew disease in hydrangea

Powdery mildew (lat. Erysiphales)

Powdery mildew fungal disease in hydrangea

First yellow and green spots can be seen on the leaves, later a gray coating forms on the underside. Affected shoots deform and die. The plant gradually wilts. For treatment, the following fungicides should be used: trichodermin, topaz, score.

Leaf spot disease (lat.Septoria)

Leaf disease in hydrangea caused by fungus - symptom brown spots

Septoria is manifested by brown spots on the leaves (lighter in the center, darker on the edges). Fully infested leaves and shoots die off. The shrub should be treated with copper sulfate or another spray containing copper to combat typical fungal diseases.

Septoria leaf spot disease

Septoria leaf spot disease in hydrangea

Ring spot disease caused by Mycosphaerella brassicicola

Ring spot disease caused by the fungus Mycosphaerella brassicicola

The bark disease is caused by the fungus Mycosphaerella brassicicola. The infection occurs most often at 16-20 ° C during wet periods and is particularly common in cabbage plants. Small spots 3 to 5 mm in diameter and up to 2 to 3 cm in size appear on the leaves. They are initially green-brown, then turn gray when dry and black when wet. A ring of chlorosis forms on the outer edge and nectoral tissue develops within the lesion. Fungicides with the active ingredient azoxystrobin from the chemical group of ß-methoxyacrylates (strobilurin derivatives) are suitable for combating ring spot disease..

Insects that transmit diseases to hydrangeas

Spider mite pests on hydrangea

Hydrangea diseases are often transmitted to healthy plants through pests. These insects include:

  • Gall nematodes
  • Spider mites
  • Vine weevil
  • Scale insects
  • Aphids

The use of insecticides from the neonicotinoid group, such as the active ingredient imidacloprid, is recommended against pests. The avermectins are also a common component of insecticides and acaricides, e.g. Vertimec pro.

Preventive measures to protect your hydrangeas

Blooming hydrangea is an eye-catcher in the garden

Since diseases develop under certain weather conditions, the risk of infection in continuous rain in summer is quite high. Preventive measures to protect the plants are therefore extremely necessary:

  • In autumn and early spring, the bushes should be treated with a copper spray against fungal diseases.
  • Before planting new plants in your garden, you should also treat the soil with a crop protection product that contains copper.
  • Old, fallen leaves and plant remains should be carefully collected.

Moderate watering, proper soil selection, and regular fertilization are essential ingredients for proper hydrangea care. If you provide your hydrangeas with ideal growing conditions and take preventative measures, they will thank you with beautiful flowers. The diseases and pests that are shown in the photos are not so bad if the necessary measures are taken in a timely manner. Is your hydrangea not blooming? Here are 8 reasons for missing flowers.