Tree diseases and tree pests

The important symptoms and characteristics of individual trees can be found in the index of deciduous trees.
Apart from tree diseases that affect the leaves, trees can also be affected by pests, fungi diseases and other damages.

Abiotic damage

abiotic damage

Hail, high winds, frost, dry spells, etc. can damage a tree. The appearance of these damages can be numerous (dried leaves, cracked bark, broken limbs). Parasites can attack the host plant in these damaged areas.



If ants are prevalent at the base of the trunk and if there is saw dust coming from the trunk, then this indicates damage to the tree. Ant colonies can be expected in the trunk as they search for a cavity or tree rot for a new home. The tree should be watched carefully because the foothold could be in danger.


Aphides affect almost all trees. They deplete the leaves of nutrients and pollute them with their excretion, known as honeydew. Over 800 species exist throughout central Europe. Normally, aphides are not harmful for the tree.

Frost Cracks

Frost cracks form because of high temperature fluctuations from the trunk center to the outside. The tree forms frost strips caused by the overlapping of bark (see photos). The crack runs almost vertical. The same affect is seen from cracks made by the sun. Should the tree show a weakening vitality, it should be evaluated. Images of a frost crack

Fungi | Mushrooms

Fungi with the hypha (mycelia), fungi diseases penetrate the wood and deplete the wood of nutrients, most importantly cellulose, polysaccharide, lignin, minerals, carbohydrates, lipids and protein. If the tree is affected then it should be evaluated. More about tree fungi.



Galls are caused mostly by gall mites. Affected mostly are the leaves of trees. Less affected are the buds, sprouts, blossoms, or branches. The distortion of the leaf does not look very good but it is not dangerous to the tree. Apart from the gall mites there are other pathogens, for example, the gall wasp.


Growth attached to a tree, such as, ivy, grapevines, and other plants do not harm the tree. If a growth becomes so prevalent that the assimilation of the tree becomes affected, then the growth should be removed.

Insect leaf damage

leaf insect damage

Insect leaf damage Insect leaf damage: Through insects like the June bug, caterpillar, and others, a tree may lose a great amount of leaves. Normally this does not pose a danger to the tree. But if a tree gets eaten bare year after year, this can affect the trees vitality.


Lichens are a symbiosis between a fungus and algae. Mostly it is tubular fungi and blue or green algae that form a living community. They also grow in extreme circumstances, but they need light and moisture. Lichens do not pose any danger to a tree. Images of Lichens

Malignant growths

Malignant growths are caused by earth rays, bacteria, and fungi. They can be life threatening to a tree. To find out the exact cause of the tree diseases, an expert should be consulted. Image of Mailganat growth


Mildew is a white covering over the leaves that can be wiped off with the fingers. In extreme cases, it should be brought under control. Images of Mildew disease

Mistletoe (Viscum album)

The mistletoe is an evergreen semi-parasite that takes away water and nutrients from the tree. An extreme case can cause a tree to die. Images of mistletoe


Mites belong to the arachnid group. They are only 0,1mm 0,5mm big and are equipped with a sting and suction ability. They affect leaves and buds. Affected leaves dry out. Extreme cases can cause the tree to weaken.

Moist Crack

moist crack
A moist crack in a tree trunk indicates decay within the trunk. The tree should be evaluated. It could be a fatal disease. Image of moist crack

Red Pustules (Nectria cinnabarina)

Red pustules are parasites in the wound that cause wilting of leaves and shoots. The orange-red boils appear in fall and winter. Affected areas should be cut back to the healthy stem. Images of red pustules


Sap is a natural defense mechanism of a tree against damage and not a tree disease. Image of sap


Shield-lice attack and damage the bark characteristics. This causes moistness in the bark. Some shield-lice also attack the leaves. Because of their tiny size, they can often be identified only after they have formed a shield-like spot with their waxy excretions. In extreme cases, an expert should be consulted.

Shoots from a trunk

Shoots from a trunk often indicate a disturbance in the tree. This can be diverse. In an extreme outbreak of shoots, consult an expert. Images of shoots from a trunk


tuber at bark of beech

Tubers are growths that are caused by fungi, insects, or other environmental influences. These are not dangerous for the tree. Image of tubers

Witches' besom

witches' besom are caused through virus diseases or fungi diseases. These are not dangerous to the tree. Images of witches' besom

Wood Destroying Insects

The spectrum of wood destroying insects is very large. Frequently it is the larva of insects breeding in wood that damage the bark and parts of the wood core, which gives fungi the opportunity to infest a tree. An evaluation from an expert is advisable. Images of wood destroying insects


Woodpeckers build their nests mostly in trees with tree rot. Tree rot is an indicator of fungal decay. The tree should be inspected. Images of damages caused by woodpeckers