Hydrangea Diseases: Identifying and Combating 12 Common Problems

No matter whether in the garden or in the tub, hydrangeas are extremely decorative ornamental shrubs with a stately size. Between June and August they impress with their large, magnificent flowers. Under optimal conditions, these attractive shrubs are relatively robust and hardly susceptible to diseases and pests. However, unfavorable site conditions or mistakes in maintenance can increase the susceptibility of this Plants for a wide variety of diseases or pest infestation significantly increase or this favor.

Problems

Common problems with hydrangeas

There are evergreen and deciduous species of the hydrangea, which differ in the height, size, shape and color of the flowers and leaves. The varieties of the farmer's hydrangea are the most popular. If the hydrangea feels comfortable in its location and if it is cared for according to its needs, it shows all its splendor. However, they are not immune to disease either. Weakened plants are particularly at risk.

Diseases

Diseases can occur, for example, when the pH value of the soil is unfavorable, the soil is too poor in nutrients, too rich in nutrients, and permanently too wet or too dry. If the location is too dark or too sunny, the plant is ailing. In addition to incorrect care and deficiency symptoms, unfavorable weather conditions can promote fungal infestation. Viruses and bacteria can also attack the plants and cause viruses or other diseases. Not to forget plant pests such as spider mites, aphids, weevils or thrips, they too can make life difficult for hydrangeas.

Treatment options

Mainly weather-related fungal diseases

Fungi are mostly the result of unfavorable weather conditions. Then they can attack hydrangeas and other plants and spread relatively quickly. If you notice a corresponding infestation, it is important to react quickly to prevent it from spreading. It is all the more important to pay attention to optimal location and housing conditions.

Powdery mildew and downy mildew

Powdery mildew is one of the diseases that can affect hydrangeas. This so-called bad weather fungus occurs above all with strong temperature fluctuations, with excessively high humidity playing a decisive role.

• Infestation recognizable by a whitish-gray, floury coating on the underside of the leaves
• Upper sides of the leaf covered with characteristic mildew stains
• Fungi spread very quickly over the entire plant
• if the infestation is obvious, start fighting as soon as possible
• heavy infestation can hardly be combated effectively
• As a first measure, completely remove infected leaves and shoots
• Always dispose of clippings in household waste or burn them
• then treat with a suitable fungicide

Infested leaves that are already on the ground must also be removed. In the case of an initial infestation, multiple sprayings with plant broths made from horsetail or tansy can be used for control. In addition, beneficial insects such as the ladybird or sawfly can be used.

Gray mold (botrytis bud rot)

Gray mold is also caused by a fungus. Cool, damp weather and splashing water can promote an infestation. It can be recognized by a gray lawn of mold on the flower buds, leaves and shoots. Often brown inflorescences also appear. Affected parts of the plant must be removed and the hydrangea then treated with suitable sprays. As a preventive measure, ensure good ventilation by repeatedly lighting the plants inside. If necessary, transplanting into lighter soil can be helpful.

Care errors

Illnesses as a result of care errors or deficiency symptoms

Problems with hydrangeas can in most cases be traced back to poor cultivation conditions. The good thing is that diseases such as chlorosis or leaf spot disease can be combated very successfully with improved conditions and the plants usually recover quickly.

Chlorosis / yellowing disease

Chlorosis can be caused by a lack of nitrogen, potassium, magnesium or iron, but also by a persistent lack of water. Signs of chlorosis are the leaves that have yellowed at the tip and turn brown when they are advanced. If this is the case in older hydrangeas, they are usually lacking nitrogen, potassium and magnesium.

If such leaf damage occurs on freshly sprouted leaves, an iron deficiency is usually the cause. This occurs mainly in soils with too high a lime content, which means that the plants cannot absorb enough iron, which leads to a deficiency. Red or pink varieties are particularly often affected because they depend on a slightly acidic pH value in the soil.

• before using any fertilizers, soil analysis is recommended
• Analysis gives certainty about which nutrients the plant is missing
• if there is a lack of nitrogen, add nitrogen in the form of a fertilizer
• Orientate the dosage to the manufacturer's specifications
• Incorporate peat, rhododendron soil or leaf compost into calcareous soil
• that makes the soil a little more acidic
• Eliminate iron deficiency by giving an iron-containing foliar fertilizer
• future use of special hydrangea fertilizers can prevent diseases

Tip: Over-fertilization should be avoided at all costs, as it can sometimes cause even greater damage to the plants.

Leaf spot disease / leaf spot fungus

A lack of nutrients, together with too high a humidity level, can promote an infestation with leaf blotch disease. It manifests itself in yellowish discolored leaves, which are covered by dark spots of different sizes. Each of these spots has a brown center. In the further course the leaf tissue thins out, the leaves fall off.

Here, too, infected parts of the plant as well as parts lying on the ground should be completely removed and disposed of with household waste. This is the only way to avoid re-infection. If the infestation is more severe, it may have to be treated with an appropriate fungicide. In order to prevent an infestation with leaf spot fungi in the future, it is advisable to light the hydrangea regularly and to avoid overly dense vegetation. This is the only way for the leaves to dry out quickly. In addition, it is important to ensure that fertilization is appropriate.

Root rot

Root rot is also one of the diseases that hydrangeas can attack. They are usually the result of too much moisture. The affected plant shows yellow, withered and drooping leaves, and the roots eventually die off. The hydrangea shows stunted growth, hardly any flowers and only weak shoots. Before root rot is identified as such, it is usually too late and the plant can no longer be saved.

However, if it is detected early on, the affected plant must be dug up immediately and rotten parts of the roots removed. Before planting, a drainage layer of gravel or coarse sand should be placed in the planting hole, which is then filled with special hydrangea soil and the hydrangea reinserted. You should then do without watering for the time being.

Viruses / bacteria

Hydrangea virus disease

The so-called hydrangea virus can be caused by bacteria (mycoplasma) as well as viruses. It can be recognized by its significantly restricted growth or because the plant and flowers remain very small. In addition, the leaves become dull and take on a purple to reddish color. Combating such highly contagious diseases is not possible, so that the affected plants inevitably have to be disposed of. Not only the plant itself but also the soil in which it stood must be generously replaced.

Tip: Planting the hydrangea again in the same place is advisable after 4 - 6 years at the earliest.

Pests

In addition to diseases, hydrangeas can also be attacked by pests. An infestation is most evident on the leaves and flowers. Here, too, it is important to check the plants regularly for an infestation in order to recognize it as early as possible and to be able to start combating it.

Spider mites

Spider mites are one of the most common pests on hydrangea. You can recognize them by the small silvery-white dots on the upper side of the leaf and later by the typical fine webs on the underside of the leaf. Most of the time the leaves roll up. Spider mites can settle most easily when the soil is permanently dry and the plant is exposed to direct sunlight.

To combat it, the first thing to do is to thoroughly shower the plant. In the case of a slight infestation, this is usually sufficient. If not, they can be treated by spraying them with sprays containing rapeseed oil. To prevent renewed infestation in the future, we recommend moving to a better, preferably partially shaded, location in evenly moist soil.

Aphids

If the plants are weakened by heat, drought or a lack of nutrients, they can also be attacked by aphids, although this is not uncommon.

• Infestation occurs mainly in spring when it is warm and dry
• Sticky honeydew on the leaves, signs of infestation
• Lice infestation attracts ants
• this favors the occurrence of soot thaw
• Soot-thaw fungi recognizable by a soot-like coating on the plants
• first control measure, rinsing the plant
• If there is an initial infestation, showering is usually sufficient

If not all the lice have been driven away, you can spray the hydrangea with self-made, diluted nettle manure. Since lice usually spread explosively, commercially available spray agents can also be used if necessary.

Root nematodes

So-called root nematodes feel very well in depleted soils. If they are present in large numbers, they can severely damage the roots of the hydrangeas. An unpleasant smell near the ground can indicate the presence of these pests. If the roots are already damaged, parts of the plant near the ground slacken until they ultimately die off.

Fighting is not possible. However, there are a number of things that can be done preventively. So you should pay attention to a needs-based supply of the hydrangeas with nutrients. It can also be useful to plant marigolds between the hydrangeas, which can successfully combat soil fatigue caused by nematodes.

Vine weevil

The black weevil likes to attack the hydrangea leaves, while its larvae prefer the roots. Eating marks on the leaf edges can be signs of an infestation. If the roots are damaged, the plant shows that it has failed to grow.

There are no special means of combating this either. You can use the approx. Collect 2 cm large black beetles. Or you can put a flower pot filled with wood wool upside down under the bush. The pests withdraw overnight so that they can be removed the next day. The larvae on the roots can be controlled with nematodes.

Thrips

Thrips, also known as bladder feet, are tiny 1 - 3 mm small, dark brown, winged pests. Their larvae do not have wings. This plant pest can develop particularly well in a dry environment. It sits mainly on the underside of the hydrangea leaves. These sucking insects leave yellowish spots on the leaves, which later turn silvery-white due to the penetrating air.

If the infestation is advanced, the leaves are heavily speckled. On closer inspection, you can also see small black dots on the leaves, the excretions of the pests. Special systemic agents for combating thrips are available on the market. In addition, natural predators such as lacewings or predatory bugs can be used.

Snails

Snails can cause great damage to a wide variety of plants, including hydrangeas. You do not disdain the foliage or the flowers and can plant completely within a short time eat bare, whereby snail species such as the Roman snail preferentially over the withered leaves make up Snails occur more frequently in damp weather. Plant residues on the ground can also attract these animals.

Fighting is usually difficult. Special slug pellets are available in stores that can be spread around the plants. Of course you can read the animals again and again, but this is not for everyone. The best way is prevention. For example, you can mix dry straw with the mulch material. The mulch layer should rather be a little thinner than too thick. Since snails are mainly active in the evening and at night, you should avoid watering in the evening and instead choose the morning hours. In addition, you should avoid sprinkling or head-over-watering, so that the leaves can always dry off quickly, because fresh, moist leaves are particularly popular with snails.