Tree diseases are often caused by microorganisms. It is mostly fungi, but bacteria and less frequently viruses can also cause the typical damage to leaves and wood. In addition, however, an unsuitable location or incorrect care also lead to symptoms of damage or make an illness possible in the first place.
Red pustule disease is very obvious
The most common tree diseases
Trees can be attacked by microorganisms and become ill as a result, or they can suffer due to an unsuitable location, too much or too little moisture and a lack of nutrients. In the case of a non-parasitic disease, however, the trees are weakened and can no longer defend themselves adequately against fungi, bacteria or viruses. Another disease is therefore often the result.
Wood-destroying tree diseases
Typical tree diseases can affect the leaves, but often also the wood. In particular, wood-decomposing fungi pose a risk. These are often invisible fungi, although species with pronounced fruiting bodies, such as honey fungus or tinder fungus, are not uncommon.
red pustular disease
This is a weakness or wound parasite that mainly affects deciduous trees. Fruit trees such as plums, cherries, apricots and all types of pome and nut fruit are often affected, as well as ornamental trees such as maple, robinia, hornbeam and box. The fungus develops mainly on dead wood and on dead parts of living trees. From there he attacks healthy parts, provided he finds branch stumps and other wounds to penetrate.
leaf spot
Leaf spots can have many different causes. In addition to fungi, bacteria and viruses, the stains can also be caused by cell sap-eating or leaf-eating pests. Leaf spot diseases caused by fungi mainly occur as a result of damp weather, particularly in late summer and autumn. Affected foliage should be generously removed, especially if it has already fallen off. The various pathogens often overwinter in it, which is why such plant material never belongs on the compost.
leaf tan
This fungal disease is a typical phenomenon of damp spring and summer weeks, which initially appears as small, roundish, reddish-brown spots on the leaves. If the damp weather persists, the spots soon cover the entire leaf. A heavy infestation can lead to leaf fall. In fruit trees in particular, the fruit can also be infected.
scab
Scab is also a common fungal disease. Infection often occurs in early spring when the temperatures are quite cool, when the spores, which are spread by wind and rain, are transferred to the leaves. Wet leaves and high humidity promote the spread. Over the summer months, new spores form again and again, which then overwinter on the ground in fallen leaves. Scab fungi are noticeable by brown, roundish spots that progressively enlarge.
shotgun disease
Shotgun disease is also a fungal disease that initially causes small, reddish to brown spots to appear on the leaves. These break out later, so that the leaves with their irregular holes appear as if they had been riddled with a shotgun shell. In the case of a severe infestation, the leaves are shed.
rust fungi
There are different types of rust fungi as they are highly specialized on certain tree species. Typical are orange-red, reddish or violet tinted leaf spots, which mainly appear on the upper side of the leaves. Infested trees should be cut back generously.
Diseases with fungal pathogens
Another fungal disease is powdery mildew, which - unlike other fungal diseases - does not need damp weather to spread. Blossom, fruit and branch monilia (“peak drought”) and wilt disease caused by various Verticillium fungi are also common in many tree species.
Diseases with bacterial pathogens
The bacterial pathogens are primarily fire blight and bacterial blight, which occurs in many trees, primarily fruit trees, and can cause considerable damage here. Like fungi, the bacteria enter the tree through wounds and other open areas and spread from there.
Typical diseases in selected tree species
The following tables provide you with an overview of what types of diseases appear on certain tree species commonly cultivated in gardens. If a tree species is not explicitly named, it is a robust species that is not very susceptible to disease - which, despite its robustness, is of course not immune to infection.
fruit trees
| fruit type | Common diseases |
|---|---|
| Apple | scab, powdery mildew, fruit tree canker, collar rot, pitting |
| pear | scab, pear rust, fire blight |
| Plums, mirabelle plums, greengage | Rust, Shotgun Sickness, Fool's or Pocket Sickness, Sharka |
| Peach apricot | Curl disease, scab, chlorosis |
| Sweet cherry, sour cherry | Shotgun disease, Monilia |
deciduous trees
| deciduous species | Common diseases |
|---|---|
| Maple (Acer) | Powdery mildew, wilt, leaf spot pathogen, leaf scorch |
| Beech (Fagus) | leaf tan |
| Oak (Quercus) | powdery mildew |
| Chestnut (Aesculus) | Powdery mildew, wilt, rust, leaf tan |
| Linden (Tilia) | leaf tan |
| Trumpet Tree (Catalpa) | wilt |
| Elm (Ulmus) | wilt |
| Willow (Salix) | Powdery mildew, rust, leaf spot pathogen |
| ornamental apple (penalty) | Powdery mildew, shotgun disease, scab |
| ornamental cherry (Prunus) | Shotgun disease, scab, wilt, leaf spot pathogen |
conifers
| conifer species | Common diseases |
|---|---|
| Araucaria (Araucaria) | needle tan |
| Yew (taxus) | wilt |
| Spruce (Picea) | wilt |
| pine (pinus) | rust |
| Larch (Larix) | gray mold rot, larch canker |
| False cypress (Chamaecyparis) | Phytophthora blight, needle tan |
| Fir (Abies) | Fir canker, rust, gray mold, needle tan |
| Juniper (Juniperus) | rust |
| Cypress (Cupressus) | Phytophthora blight |
tips
Most tree diseases can be kept in check quite well if the crown is kept light - this way the leaves dry off faster and there is also enough light and air inside the tree crown.