Tree diseases from A-Z

If a tree is not doing well, there can be various reasons: from damage caused by frost to an infestation with animal pests. Tree diseases, which are triggered by an infection with microorganisms, should be taken seriously. These diseases pose a serious threat to the tree. While care mistakes or a pest infestation can usually still be contained well, an infection is very difficult to treat.

diagnosis

Only an exact diagnosis can show what caused the disease in the tree. It is important to find out whether the tree disease is parasitic or non-parasitic. It must also be clarified whether there is an infectious disease or a pest infestation that needs to be treated.

Nonparasitic damage

• frost damage
• Damage from drought
• disorders in nutrient absorption
• 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 (freshwood and drywood insects)
• Mushrooms
• viruses
• bacteria

Nonparasitic causes of damage

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

Omorika dying

The needles of the Serbian spruce (Omorika spruce) occasionally lighten in late summer or autumn, later the needles turn brown and fall off. If needle throwing occurs over a long period of time, the entire tree can die. The shoot tips of the tree are particularly affected. The reason for this lies in a disturbed nutritional status.

Caused

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

Measures

Potassium-rich fertilizers and/or lime should not be used on Omorika spruces. A complete mineral fertilizer, Epsom salt and a special magnesium fertilizer are recommended in spring.

parasitic diseases

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

fungal diseases

Tree diseases caused by fungi can mainly be counteracted preventively. Once the infection is visible, there is usually no pesticide to kill the pathogen. If the infestation has not progressed very far, the spread can be contained by generously cutting diseased parts of the plant down to the healthy wood. Fungal infections tend to occur in damp weather.

wilt pathogen

In addition to a lack of water and waterlogging, fungal pathogens in particular can be the cause of the withering 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 picture

The young shoots and the flowers of deciduous and coniferous trees suddenly become limp and brown. Double flowers that don't dry well will rot. If the moisture persists for a long period of time, a gray down will form on the flowers.

affected plants

almost all deciduous and coniferous trees

Measures

Immediately cut out affected parts of the plant generously. Avoid nitrogen-rich fertilizers and ensure that the shoots are well ventilated.

Monilia peak drought

The fungus (Monilia laxa) penetrates the trees through the flowers and can cause entire branches to die off in the event of rain or increased dew formation.

damage picture

During and after flowering, the flowers and leaves at the tips of the shoots turn brown and hang limply.

Affected shrubs

• almond bush
• ornamental cherry

Measures

Cut back all dead shoots back to 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 promote an infestation with stem and root rot, which is caused by the fungus Phytophthora.

damage picture

In the lower trunk area, violet discolored, spongy rotting spots that smell of bitter almonds form. The leaves of infected trees turn pale green and curl up at the tips of the branches. The pathogen can kill the entire tree.

Affected shrubs

all types of wood

Measures

Generously cut out all rotten areas down to the healthy tissue. Relocate the tree (if possible) and provide a well-drained substrate. In extreme cases, dead plants must be removed as early as possible. No tree or shrub may be planted at the same location for several years.

whorl fungus (Verticillium wilt)

The whorl fungus (Verticillium) enters the tree via the roots, spreads via the drainage tracts and clogs them, thereby impairing water transport. In addition, the whorl fungus excretes toxins that cause the leaves to wither. A definitive diagnosis can only be made by a laboratory.

damage picture

Individual branches suddenly wither and die. The disease is often only visible on one side. The symptoms are particularly pronounced during dry periods, which occur in early summer.

Affected shrubs

• vinegar tree
• fan maple
• tree of gods
• Japanese maple species
• chestnut
• magnolia
• smoke bush
• trumpet tree

Measures

Avoid wet locations that are slow to warm up in spring. When the infestation begins, cut back all infected branches down to 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 thinning cut is essential. Not all leaf spots are of parasitic origin, often extreme temperature fluctuations or nutrient problems are to blame, or it is sunburn.

leaf tan

In addition to the leaf miner, leaf tan caused by the fungus Guignardia aesculi is the most common pathogen on horse chestnuts. Plane trees are occasionally infested with leaf tan, which is caused by the pathogen Apiognomonia veneta. The tree disease develops preferentially on the bark and progressively spreads to the leaves as well. The fungus overwinters in the bark and autumn leaves.

damage picture

Local cell death occurs in the form of brown, sunken spots (leaf necrosis) on the foliage, which can penetrate the leaf veins. With severe necrosis, the leaf edge curls up and the leaves fall off prematurely. The leaves of plane trees turn black from the leaf veins.

Affected shrubs

• buckeye
• plane

Measures

Remove fallen leaves to prevent reinfection.

scabs

In damp spring weather, the spores of these fungi can hibernate on dead foliage and infect the trees.

damage picture

Olive-brown to black colored spots on the leaves, fruits and flowers of various tree species. The shoot tips die off.

Affected shrubs

• Firethorn
• ornamental apples
• different deciduous trees

Measures

Plant hardy varieties and remove foliage in the fall. A clear cut provides better ventilation in the crown.

shotgun disease

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 picture

Red-brown spots form on the leaves, which later fall out of the leaf tissue, leaving holes that look like they were caused by a shotgun blast.

Affected shrubs

• ornamental cherry
• ornamental plum
• bay cherry

Measures

Optimal location and 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 at night.

Juniper rust/pear grating

Especially in regions close to cities, rust infections on juniper trees have been occurring again and again lately. This is an infestation with the fungus Gymnosporangium fusum, which also occurs on the pear (pear rust).

damage picture

In spring, cone-shaped, yellowish-brown structures grow up to two centimeters long on the branches. The branches of the juniper begin to twist and die.

Infested shrubs

• juniper
• Pear
• hawthorn
• rowanberry
• apple tree
• rock medlar

Measures

If the above trees are cultivated in the garden, they must be planted at least 800 m apart. Since there are hardly any gardens of this size, a joint cultivation is not recommended. At an early stage, it is possible to cut out affected parts of the branch. There is no antidote to the fungus.

Weymouth pine blister rust

Infections with the fungus Cronartium ribicola occasionally occur in spring on five-needle pines such as the white pine.

damage picture

Pea-sized yellow blisters grow out of the bark and release yellowish spore powder. The bark is cracked and there is heavy resin flow. The fungus is also found on blackcurrants (currant columnar rust) and is able to switch hosts. Affected trees usually die after a few years.

Infested shrubs

• white pine
• stone pine
• white pine
• brush pine

Measures

Remove infested trees from the garden immediately. Do not cultivate blackcurrants with these trees in the garden.

powdery mildew

The Powdery Mildew (Erysiphales) is a fungus that can affect almost all plant species. 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 picture

Clearly visible white deposits on the upper side of the leaves, on flowers and fruits. The fungus penetrates the leaf tissue and feeds there. Young shoots and leaves are wavy, curled up or misshapen. Later, brown or black fruiting bodies form on the white coating.

Infested shrubs

almost all types of wood

Measures

The mycelium overwinters in the buds or on the shoots. These must be cut out. The fungus cannot survive on dead leaves.

wood destroying fungi

These fungi prefer to attack severely weakened trees or dead tissue.

red pustular disease

Red pustule disease (Nectria cinnabarina) can be seen most clearly in winter. The fungus breaks down dead wood and can kill the entire tree.

damage picture

Numerous vermilion, pinhead-sized pustules appear on bare branches or the trunk.

Infested shrubs

• aged hornbeam hedges
• frost-damaged trees and shrubs in unfavorable locations

Measures

Cut out diseased parts of the plant and dispose of with household waste. Endangered and infected trees must not be too dry, so penetrating watering is necessary.

Bacterial pathogens

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

fire blight

Fire blight is a dangerous tree disease and the most important bacterial disease of pome fruit, caused by the bacterium Erwinia amylovora. 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 picture

When infected, the leaves, flowers and fruits turn dark brown to black and appear burnt. Shoot tips curve like hooks, the foliage dries up and shrivels. Milky droplets (bacterial mucus) escape when the humidity is high.

Infested shrubs

• Apple
• pear and pear
• quince
• all hawthorn species
• Firethorn
• Pear
• mountain ash (rowanberry)
• all medlar species
• quinces

Measures

Fighting is currently not possible. In the case of fresh infections, cut back infected shoots far into the healthy wood, remove them from the property in a plastic bag and dispose of small amounts with the residual waste. Alternatively, burn larger quantities. Fire blight is notifiable, so the plant protection authority must be informed.

overview

Some tree species are particularly susceptible to certain diseases. If damage to the plant is recognizable, 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 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, mealybugs and scale insects, weevils)
• Spruce (Picea): wilt pathogen (pests: spider mites, aphids, leaf miners)
• Pine (Pinus): rust (pests: mealybugs and scale insects, sawflies, various butterflies)
• Arborvitae (Thuja): no common tree diseases (pests: leaf miners and spider moths)
• Juniper (Juniperus): rust (pests: spider mites, mealybugs and scale insects, leaf miners)

Shrubs

• Maple (Acer): wilt pathogens, leaf spot pathogens, leaf smut, 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, sawflies, caterpillars such as the oak processionary moth, leaf beetles)
• Firethorn (Pyracantha): Scab (Pests: Sawflies)
• Hornbeam (Carpinus): rare in healthy plants (pests: spider mites, gall mites, aphids and butterflies)
• Chestnut (Aesculus): wilt pathogens, leaf scorch, rust and powdery mildew (pests: leaf miners and spider moths, butterflies)
• Lime (Tilia): leaf tan (pests: spider mites, gall mites, aphids, mealybugs and scale insects)
• Sycamore (Platanus): leaf tan (pests: leaf miners and spider moths)
• Robinia (Robinia): only rarely get sick (pests: gall mites, leaf miners and spider moths)
• Trumpet tree (Catalpa): wilt pathogen (pests: hardly known)
• Elm (Ulmus): wilt pathogens (pests: gall mites, aphids, mealybugs and scale insects, leaf sucker fleas)
• Willow (Salix): leaf spot pathogen, rust, powdery mildew (pests: spider mites, gall mites, sawflies, butterflies, leaf beetles)
• Hawthorn/hawthorn (Crataegus): leaf spot pathogen, rust (pests: spider mites, aphids, butterflies)
• Crabapple (malus): scab, buckshot, powdery mildew (pests: aphids, mealybugs and mealybugs, butterflies, weevils)
• Ornamental cherry (Prunus): wilt pathogen, leaf spot pathogen, scab, buckshot (pests: aphids, sawflies, leaf miners and spider moths, butterflies)

preventive measures

You can do a number of things to prevent the tree from becoming ill when choosing the type of tree and the location. If possible, use resistant tree species and also pay attention to optimal site conditions. Balanced fertilization, which should not be too nitrogenous, increases the tree's resilience. Also make sure that wounds caused by storms or frost are reduced to a minimum as soon as possible. Who regularly clears the wood of dead branches and also occasionally one thinning cut, so that the crown is well ventilated, thus preventing excessive accumulations of moisture. A crucial factor in preventing infection and consequent disease of the tree.

Conclusion

Regular control of the trees and shrubs in the garden is absolutely necessary in order to detect 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.

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