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The gardener can already look forward to a rich fruit harvest during the flowering period in spring. However, apples, pears and the like are at risk if fungal diseases spread rapidly, particularly as a result of incorrect care, an unsuitable location or during a wet summer. Tree and fruit-friendly countermeasures only help if the damage is detected early. Chemical sprays, on the other hand, should remain the exception, especially in hobby gardens and orchards.
fungal diseases from trees
causes
Mushrooms and trees have always formed an often indispensable, but sometimes fatal alliance. While many forest fungi live together with some tree species in a symbiosis that is valuable and vital for both partners, other fungi on fruit trees cause serious diseases. In these species, the pathogen is often not visible to the naked eye, only the symptoms and the consequences of its invasion and growth are visible to the viewer.
Fungal diseases rarely appear “just like that”, but always have a cause. These must be recognized and eliminated in order to get the problem under control and to treat the infested trees successfully. Infections with unwanted fungal pathogens mainly occur on these occasions:
- humidity: for example in rainy summers or wet winters
- injuries: for example as a result of pruning in damp weather
- frost: if the bark bursts in severe frost and sunshine at the same time, fungi can penetrate
- blossom: fungal pathogens infect the fruit tree blossom, disease often only becomes apparent when the fruit is ripe
- leaves: infected foliage left in fall or used for mulching transmits fungal spores
- pruning: seldom pruned trees develop dense crowns that provide a breeding ground for fungal diseases due to non-drying moisture
- planting distance: close planting distance promotes fungal infections
Furthermore, fungi infect previously damaged trees particularly frequently. Fruit trees that are weakened by an unsuitable location and/or inadequate care belong to the risk group for a fungicidal infestation: After all, the natural defense mechanisms of these trees are no longer able to oppose the pathogens.
Prunus avium, wild cherry, sweet cherry
Prevent
If you know the causes of possible fungal diseases, you can counter them with appropriate preventive measures. These include above all:
- Compliance with the recommended planting distance
- Choosing a suitable location (sunny, sheltered, not too humid)
- regular pruning for thinning
- Treatment of cuts (e.g. by brushing with tree sap)
- Removal and disposal of autumn leaves (possibly with household waste)
- Needs-based care (watering, fertilizing)
- Oversupply is just as harmful as undersupply
Furthermore, when pruning the fruit trees, you should only ever use sharp and always disinfected cutting tools in order to prevent transmission from one tree to another in this way. For this purpose, for example, an at least 70% alcohol solution is suitable.
tip: Some types of fruit are particularly sensitive to certain fungal diseases. Instead of fighting them again and again, it is better to choose resistant varieties from the outset when planting. This applies, for example, to scab-resistant apple varieties, mildew-resistant gooseberry varieties or sweet and sour cherries that are less sensitive to Monilia.
Identify the 10 most common fungal diseases on fruit trees
There are countless fungal pathogens, but they prefer to attack only certain or related types of fruit. Others are found exclusively on berries or pome fruit. However, a few pathogens are real generalists and do not stop at any fruit tree. This includes, for example, the widespread Monilia fruit rot. At this point we briefly explain the 10 most common fungicidal diseases on fruit trees, how you can recognize and combat them.
1. Apple scab
Scab disease, caused by the fungus Venturia inaequalis, primarily affects apple trees, but can also occur on pears, cherries and peaches. The disease is manifested by brown-black mottled leaves that are soon shed and later star-shaped cracks on the fruit. The fruits are basically still edible, but rot quickly and can therefore not be stored.
Scab occurs mainly after a mild and wet spring and when the trees grow too dense due to insufficient pruning and therefore dry poorly. Plant preferably resistant or non-sensitive varieties. Treat an infested fruit tree with a copper-containing fungicide, and the fallen leaves should be removed and disposed of - the fungal spores overwinter in them.
2. Pear grating
Pear rust only affects pear trees, which develop conspicuous, wart-shaped and yellow-brown spots on the leaves after infection from May. However, the disease affects not only foliage development, but also growth and fruit harvest. Cut infested trees back to healthy wood and dispose of the clippings with household waste or burn them. Since the causative fungus overwinters on neighboring juniper bushes, you should also remove them.
3. Leaf tan
You can recognize the leaf tan by the eponymous brown foliage, which is shed prematurely in the middle of summer. The fruits of infected trees are not edible and, like the infested foliage, should be removed and disposed of as early as possible - but definitely not in the compost! A strong pruning is essential. The pathogen primarily affects cherries, apricots and quinces, but sometimes also apple and pear trees.
Leaf tan on a quince leaf
4. Powdery mildew
Powdery mildew diseases are also common on fruit trees. However, the gardener differentiates between two forms: The powdery mildew, also known as fair-weather mildew, occurs primarily in warm weather and sunshine. It is shown by a whitish growth of fungus on leaves and shoots, which can be easily wiped off with the fingers. the downy mildew On the other hand, it shows up in cool and rainy summers when the leaves have no opportunity to dry off and the fungal spores can penetrate.
The so-called apple powdery mildew shows up early on the young leaves, as it overwinters directly on the tree in its leaf scales. Remove the affected leaves and spray the trees several times, every few days, with a mixture of whole milk/raw milk and water (1 part water, 5 parts milk) or whey and water (ratio 1:1). If this home remedy does not help, you can use a fungicide. When planting, give preference to apple varieties that are resistant to powdery mildew.
5. Monilia fruit rot
The fruit rot caused by fungi of the genus Monilia affects almost all types of fruit grown in Germany. Symptoms of the disease are the characteristic rotten spots with the round cushions of mould. The fruits are no longer edible and should be removed and disposed of with household waste. In order to prevent Monilia fruit rot, you should never leave any leftover fruits (so-called "fruit mummies") hanging over the winter months, but dispose of them in autumn, just like the leaves.
6. Fruit tree canker
Fruit tree canker, which occurs frequently and primarily in apple and pear trees, is caused by fungi of the species Nectria galligena. It mainly occurs in regions with a high rainfall. Typical features of an infection are:
- sunken, brown-red spots on the bark
- cracking bark
- withering branches and shoots
- bulging
The disease can only be combated by completely removing affected parts of the plant, whereby you should treat larger wounds with a wound sealant after pruning. To avoid re-infection, dispose of the clippings, infested fruit and fallen leaves.
Fruit tree canker on an apple tree
7. Red pustular disease
Above all, stone fruit of the Prunus genus, such as plums and apricots, but also cherries and all types of pome and nut fruit can be attacked by pathogens of the red pustule disease. These penetrate living trees through dead plant parts - such as twigs and branches frozen back in winter or fruit mummies - and attack healthy parts of the plant from here. To prevent this, you should always cut away dead branches and twigs and leave no stubs behind.
8. Sooty spot disease
If a black, sooty coating appears on ripe fruits, then it is the sooty blotch disease. The stains are only superficial on the fruit peel and can be removed by thorough washing. Once removed, you can safely eat infected fruit. The disease cannot be fought, it can only be prevented by taking appropriate measures. Infested fruit should always be removed.
9. Spray spot disease
The so-called spray spot disease only appears on sweet and sour cherries. The treatment is carried out through the use of herbal tonics, which you can purchase in specialist shops or prepare yourself. Field horsetail broth, for example, has proven to be generally effective for combating fungal diseases, but it must be used early and preventively.
The spray spot pathogen always overwinters in fallen foliage and reinfects the trees the following spring around the time of flowering. For this reason, the old leaves should be carefully collected and disposed of in autumn.
10. Verticillium wilt
In contrast to many other fungal pathogens, Verticillium fungi do not penetrate the fruit tree via the leaves or injuries to the bark or wood, but from the ground. They penetrate the pathways through damage to the roots and clog them, so that affected fruit trees suddenly begin to wither. The signs of wilting first appear on individual branches, but soon spread to the entire tree. A rescue is usually not possible, so that only the clearing remains. Verticillium wilt is usually caused by a substrate that is too damp or waterlogging.
Verticillium in branch cut
tip: Fungal diseases can be avoided by not pruning the trees when it is raining or generally damp weather. Even in frost, the pruning shears should stay in the shed.