Tree diseases from A-Z

If a tree is not doing well, it can have different causes: from damage caused by frost to infestation with animal pests. Tree diseases that are triggered by an infection with microorganisms are to be taken really seriously. These diseases pose a serious threat to the tree. While care errors or a pest infestation can usually still be contained well, an infection is very difficult to treat.

diagnosis

What caused the disease in the tree can only be shown by an exact diagnosis. It is important to find out whether it is a parasitic or non-parasitic tree disease. In addition, it must be clarified whether there is an infectious disease or a pest infestation that needs to be treated.
Non-parasitic damage

• Frost damage
• Damage from drought
• Disturbances in nutrient uptake
• excessive wetness
• Environmental influences such as exhaust fumes, road salt and acid rain

Parasitic causes of damage

• Small mammals
• other pests such as insects and their larvae (fresh wood and dry wood insects)
• mushrooms
• Viruses
• bacteria

Non-parasitic causes of damage

The proportion of non-parasitic damage to trees is very high. It is not always insects or microorganisms to blame that the tree is sick. The most common causes include the effects of special site conditions, weather conditions or nutrient and water supplies. Each individual tree species has very specific requirements in terms of soil, lighting conditions and climatic requirements. The more these conditions deviate from the species-specific optimum at home, the more susceptible the tree becomes to diseases and pests. Examples of non-parasitic tree diseases include:

Omorikasterben

On the Serbian spruce (omorika spruce), needle lightening occasionally occurs in late summer or autumn, later the needles turn brown and fall off. If the needle throw occurs for a long time, the entire tree can die. The shoot tips of the tree are particularly affected. The reason for this lies in a disturbed nutritional state.

• Root cause: This disease usually occurs in moderately acidic or heavily compacted loam or clay soils that tend to waterlogging. The magnesium supply is particularly important for this species of spruce. If the soil contains a lot of potassium, this leads to a reduction in the absorption of magnesium.

• Measures: Omorika spruce must not be supplied with fertilizers containing potassium and / or lime. A full mineral fertilizer, Epsom salt and a special magnesium fertilizer are recommended in spring.

Parasitic diseases

If a tree is sick, it must first be found out whether it is a real disease or an infestation with a pest from the insect kingdom. Microorganisms penetrate primarily through wounds into the ducts of the trees and can infect the whole tree through the ducts. The most common cause of disease are fungi, but there are also tree diseases caused by viruses or bacteria.

Fungal diseases

Tree diseases caused by fungi can mainly be countered preventively. Once the infection is visible, there is usually no pesticide available to kill the pathogen. If the infestation has not yet progressed very far, it can be prevented from spreading by cutting diseased parts of the plant generously into the healthy wood. Fungal infections tend to occur in damp weather.

Wilt pathogen

In addition to lack of water and waterlogging, fungal pathogens in particular can be the cause of the wilting of the trees.
Gray mold
In spring, when the weather is damp and cold, the young shoots and flowers of various trees and shrubs can be attacked by gray mold (Botrytis cinerea).
Damage: The young shoots and the flowers of deciduous and coniferous trees suddenly become limp and brown. Double flowers that do not dry well rot. If the moisture persists over a longer period of time, a gray fluff will form on the flowers.
Affected plants: almost all deciduous and coniferous trees
Measures: Immediately cut out the infected parts of the plant generously. Avoid nitrogenous fertilizers and ensure that the shoots are well ventilated.
Monilia peak drought
The fungus (Monilia laxa) penetrates the woody plants through the flowers and can cause entire branches to die off when it rains or when there is increased dew formation.
Damage: During and after the flowering period, the flowers and leaves at the shoot tips turn brown and hang limply.
Affected trees:

• Almond bush
• Ornamental cherry

Measures: Cut all dead shoots back into the healthy wood as early as possible. Treatments with fungicides for prevention are possible. Please note the current information from the plant protection office!
Stem and root rot
Compacted soil and waterlogging favor an infestation with the stem and root rot, which is triggered by the fungus Phytophthora.
Damage: In the lower trunk area, purple discolored, spongy rot areas that smell of bitter almonds form. The leaves of infected trees turn pale green and curl up at the tips of the branches. The whole tree can die off due to the pathogen.

Affected trees: all types of wood

Measures: Generously cut out all the rotten areas down to the healthy tissue. Move the tree (if possible) and make sure that the substrate is well drained. In extreme cases, dead plants must be removed as early as possible. No tree or shrub may be planted in the same location for several years.
Whorl fungus (Verticillium wilt)
The whorl fungus (Verticillium) penetrates the tree via the roots, spreads via the ducts and clogs them, thereby impairing the water transport. In addition, the whorl fungus excretes toxins that cause the leaves to wilt. A clear diagnosis can only be made by a laboratory.
Damage: Individual branches suddenly wilt and die. Often the disease is only visible on one side. The symptoms are particularly pronounced in dry periods that occur in early summer.
Affected trees:

• Vinegar tree
• Japanese maple
• Tree of gods
• Japanese maple species
• chestnut
• magnolia
• Wig bush
• Trumpet tree

Measures: Avoid wet locations that are slow to warm up in spring. When the infestation begins, cut back all infected branches into the healthy wood.

Leaf spot pathogen

Very dense vegetation, poorly ventilated locations and years with frequent rain showers and high humidity promote these tree diseases. In order to prevent susceptibility, a professional clearing cut is essential. Not all leaf spots are of parasitic origin; strong temperature fluctuations or nutrient problems are often to blame, or it is sunburn.

Leaf tan

In addition to the leaf miner, the tan caused by the fungus Guignardia aesculi is the most common pathogen on horse chestnuts. In plane trees there is occasionally an infestation with the leaf tan, which is caused by the pathogen Apiognomonia veneta. The tree disease develops preferentially on the bark and progressively spreads to the leaves. The fungus overwinters in the bark and autumn leaves.
Damage: Local cell death occurs in the form of brown, sunken spots (leaf necrosis) on the foliage that the leaf veins can overcome. With severe necrosis, the leaf edge rolls up and the leaves fall off prematurely. The leaves of plane trees turn black from the leaf veins.
Affected trees:

• buckeye
• plane

Measures: Get rid of fallen leaves to prevent re-infection.

Scab fungi

In damp weather in spring, the spores of these fungi can overwinter on the dead leaves and infect the trees.
Damage: Olive-brown to black spots on the leaves, fruits and flowers of various tree species. The shoot tips die off.
Affected trees

• Firethorn
• Ornamental apples
• different deciduous trees

Measures: Plant hardy varieties and remove the foliage in the fall. A clearing cut ensures better ventilation in the crown.

Shotgun Sickness

In addition to a fungal infection, there are many other causes of shotgun disease. The affected trees should therefore be examined in the laboratory.
Damage: Red-brown spots form on the leaves that later fall out of the leaf tissue, leaving holes that look like they were caused by a shot with a shotgun.
Affected trees

• Ornamental cherry
• Ornamental plum
• Laurel cherry

Measures: Optimal location and a balanced water supply are very important. Mulch the trees and do not spray the foliage with water in the evening so that the leaves are dry during the night.

Juniper grate / pear grate

Rust infections on junipers have recently been occurring again and again, especially in urban areas. This is an infestation with the fungus Gymnosporangium fusum, which also occurs on the pear (pear grate).
Damage: In spring, cone-shaped, yellowish-brown structures up to two centimeters long grow on the branches. The branches of the juniper begin to twist and die.
Infested trees:

• juniper
• pear
• Hawthorn
• Rowanberry
• Apple tree
• Loquat

Measures: If the trees mentioned above are cultivated in the garden, they must be planted at a minimum distance of 800 m. Since there are hardly any gardens of this size, joint cultivation is not recommended. At an early stage, it is possible to cut out the affected branches. There is no control agent against the fungus.

White jaw rust

Infections with the fungus Cronartium ribicola occasionally occur in five-needle pines such as the Weymouth pine in spring.
Damage: Pea-sized yellow bubbles grow out of the bark, releasing yellowish spore powder. The bark is cracked and there is a strong flow of resin. The fungus is also found on the black currant (currant column rust) and is able to change hosts. Infested trees usually die after a few years.
Infested trees:

• White pine
• Swiss stone pine
• Girl's jaw
• Brush Jaw

Measures: Immediately remove infected trees from the garden. Do not cultivate black currants with these trees together in the garden.

Powdery mildew

Powdery mildew (Erysiphales) is a fungus that can attack almost all types of plants. In contrast to all other types of fungus, powdery mildew is a so-called fair-weather fungus that occurs in warm, dry weather periods.
Damage: Clearly visible white deposits on the upper side of the leaf, on flowers and fruits. The fungus penetrates the leaf tissue and feeds there. Young shoots and leaves curl, curl up or are deformed. Brown or black fruiting bodies later form on the white coating.
Infested trees: almost all types of wood
Measures: The fungal network overwinters in the buds or on the shoots. These have to be cut out. The fungus cannot survive on dead leaves.

Wood-destroying fungi

These fungi preferentially attack severely weakened trees or dead tissue.

Red pustular disease

Red pustular disease (Nectria cinnabarina) can be seen most clearly in winter. The fungus breaks down dead wood and can cause the entire tree to die.
Damage: Numerous vermilion-red pustules the size of a pinhead appear on bare branches or the trunk.
Infested trees:

• aged hornbeam hedges
• trees damaged by frost in unfavorable locations

Measures: Cut out sick parts of the plant and dispose of them in household waste. Endangered and infected trees must not stand too dry, therefore thorough watering is necessary.

Bacterial pathogens

In addition to fungi, bacteria can also penetrate the tree through injuries and cause damage there. There are a number of bacterial pathogens that can infect both deciduous and coniferous trees. The most common include:

Fire blight

Fire blight is a dangerous tree disease and the most important bacterial disease in pome fruit caused by the Erwinia amylovora bacterium. It can spread like an epidemic. The bacteria block the plant's immune system. As a rule, infections occur during the flowering period when warm, humid weather conditions prevail at the same time.
Damage: When infected, the leaves, flowers and fruits turn dark brown to black and look like they have been burned. Shoot tips curve like hooks, the foliage dries up and shrinks. When the air humidity is high, milky drops (bacterial slime) appear.
Infested trees:

• Apple
• Pear and rock pear
• quince
• all hawthorn species
• Firethorn
• pear
• Mountain ash (rowan berry)
• all medlar species
• Quinces

Measures: Control is currently not possible. In the case of fresh infections, cut back infected shoots well into the healthy wood, remove them from the property in a plastic bag and dispose of small amounts in the residual waste. Alternatively, burn larger quantities. Fire blight is notifiable, so the plant protection authorities must be informed.
Tip: Only use sterile tools to cut out diseased shoots, which you disinfect again after each cut (for example with alcohol). Otherwise you may also infect the healthy shoots!

overview

Some tree species are particularly susceptible to certain diseases. If damage to the plant can be seen, it does not always have to be a tree disease. In many cases, animal pests are at work. A detailed examination of the tree usually already provides information as to whether it is a matter of "real tree diseases" or an infestation with insects.
Conifers

• Yew (Taxus): wilt pathogen (pests: gall mites, woolly and scale insects, weevils)
• Spruce (Picea): wilt pathogen (pests: spider mites, aphids, leaf miners)
• Pine (Pinus): rust (pests: mealybugs and scale insects, sawfly, various butterflies)
• Tree of life (thuja): no common tree diseases (pests: leaf miners and web moths)
• Juniper (Juniperus): rust (pests: spider mites, woolly and scale insects, leaf miners)

Shrubs

• Maple (Acer): wilt pathogen, leaf spot pathogen, leaf tan, powdery mildew (pests: gall mites, cicadas, aphids, mealybugs and scale insects, butterflies)
• Birch (Betula): no common diseases known (pests: aphids, leaf bugs, leaf miners and spider moths)
• Beech (Fagus): leaf tan (pests: gall mites, aphids, mealybugs and scale insects, butterflies)
• Oak (Quercus): powdery mildew (pests: spider mites, aphids, sawfly, caterpillars such as the oak processionary moth, leaf beetles)
• Firethorn (Pyracantha): scab (pests: sawfly)
• Hornbeam (Carpinus): rare in healthy plants (pests: spider mites, gall mites, aphids and butterflies)
• Chestnut (Aesculus): wilt pathogen, leaf tan, rust and powdery mildew (pests: leaf miners and web moths, butterflies)
• Linden (Tilia): leaf tan (pests: spider mites, gall mites, aphids, woolly and scale insects)
• Sycamore (Platanus): leaf tan (pests: leaf miners and web moths)
• Robinia (Robinia): rarely become ill (pests: gall mites, leaf miners and web moths)
• Trumpet tree (Catalpa): wilt pathogen (pests: hardly known)
• Elm (Ulmus): wilt pathogen (pests: gall mites, aphids, mealybugs and scale insects, leaf sucker fleas)
• Willow (Salix): leaf spot pathogen, rust, powdery mildew (pests: spider mites, gall mites, sawfly, butterflies, leaf beetles)
• Hawthorn / hawthorn (Crataegus): leaf spot pathogen, rust (pests: spider mites, aphids, butterflies)
• Ornamental apple (Malus): scab, shotgun, powdery mildew (pests: aphids, mealybugs, mealybugs, butterflies, weevils)
• Ornamental cherry (Prunus): wilt pathogen, leaf spot pathogen, scab, shotgun (pests: aphids, sawfly, leaf miners and web moths, butterflies)

Preventive measures

When choosing the type of tree and its location, you can do a lot against a possible disease of the wood. If possible, use resistant tree species and also ensure that the site conditions are optimal. A balanced fertilization, which should not be nitrogen-stressed, increases the tree's resilience. You should also ensure that wounds caused by storms or frosts are reduced to a minimum as soon as possible. Who regularly clears dead branches from the wood and occasionally one Carries out a clearing cut so that the crown is well ventilated, thus preventing excessive Moisture build-up. A decisive factor in the prevention of infections and thus diseases of the tree.
Tip: If you are unsure of what disease the tree is suffering from, it is best to contact an expert. In an emergency, you may be able to prevent felling or further spread of the disease.
Conclusion
Regular inspection of the trees in the garden is essential in order to identify possible diseases at an early stage. This is the only way you can intervene when it is still possible - and often with very simple measures.