Apples are healthy and they still taste best from your own tree. When looking for the right apple variety, you can choose between different flavors, colors and harvest times. In some cases, one pollinator variety can even be dispensed with. But despite all the joy about self-harvested fruit, apple trees can also be affected by disease or pests. Yellow, mottled leaves or premature leaf drop can indicate this.
Causes of leaf damage on apple trees
If the apple tree shows yellow, brown-spotted leaves or loses its leaves prematurely, this can have several causes. These symptoms usually occur together with others, so that the exact cause is not so easy to identify. In addition, many apple varieties have poor resistance, which increases their susceptibility. Fungal diseases and pests can be responsible for such damage, and physiological disorders, i.e. stress, cannot be ruled out as a cause.
Diseases
apple scab
Apple scab, a disease caused by the sac fungus Venturia inaequalis, is one of the most important apple tree diseases. High temperatures and humidity in spring or long-lasting leaf wetness favor an infestation. But small brown spots on and under the leaves, which slowly grow larger and converge, can also be a sign of an infestation. In the case of early infestation, often only the tips of the sepals are affected, later usually the whole leaf. Then they die and the tree wilts.
apple scab
combat
Since this fungus overwinters in the foliage, fallen leaves should be completely removed from the ground. Because otherwise a renewed infestation is inevitable. A layer of mulch on the tree disc can be helpful to inhibit the development of the fungus, but not right up to the trunk and no bark mulch. The crown should also be thinned out by regular pruning in winter so that the inside of the crown is better ventilated.
tip: In order to counteract diseases in general, one should opt for resistant varieties when buying.
collar rot
- Collar rot caused by fungi of the genus Phytophthora
- Trees show reduced growth
- Foliage initially yellowish, later reddish
- Tree loses foliage prematurely
- Fruits remain smaller, are more intensely colored (emergency ripening)
- Individual branches die off
- Because disease progresses slowly
- Apple tree dies within two to four years
combat
In the case of a light infestation, cut off the affected parts of the plant and treat the resulting cuts with an anticancer agent. But if the collar rot is already advanced, the apple tree usually has to be felled. Nevertheless, as a preventive measure, one should pay attention to resistant varieties, avoid injuries to the grafting area and regularly remove fallen fruit. In addition, the tree disc should be covered with compost or mulch in such a way that around 10 cm remain free around the trunk.
Marssonina leaf spot disease
- Occurs around July and August, during longer periods of rain
- Fungus Diplocarpon mali overwinters in fall foliage
- Infects the leaves at the beginning of the flowering period
- Permanently wet leaves and temperatures above 20 °C favor an infestation
- Affected foliage is mottled brown
- Spots blend into each other over time
- Later discolored extensively yellow
- Partly necrotic mottled with red-violet bordered spots
Marssonina leaf spot on rose leaf
Fungicides, which are also used to combat apple scab and apple powdery mildew, are suitable for combating this. Regular fruit tree pruning ensures that all areas are well ventilated.
tip: Careful removal of fallen leaves in autumn reduces the risk of reinfestation.
pest infestation
Pest infestation occurs mainly in spring and summer. Some pests use the apple tree as a breeding ground for their offspring, which then eat young leaves, shoots and flower buds after the winter. Several pests are possible causes of the leaf damage mentioned.
apple rust mites
- Indications of the apple rust mite are the undersides of the leaves, which are initially yellowish and later mottled with rusty-brown
- The upper side of the leaf is dull and lackluster
- As a countermeasure, remove infested branches and use natural predators such as predatory mites
- Do not dispose of clippings in the compost
fruit tree spider mite
- causes fine whitish leaf spots
- Foliage later dull, silvery-bronze discolored, tree loses foliage early
- Negative effects on flower bud set and fruit colour
- Control by natural enemies such as lacewings, ladybugs and spiders.
- Use of chemical sprays in spring only in exceptional cases, they also kill the natural enemies of the mites
apple bug
- Small holes and brown leaf spots can indicate apple bugs
- Growth of young shoots is interrupted, fruits show corky spots
- Pests can be shaken off early in the morning, minimizing infestation
- Use insecticides only in severe infestations.
Northern apple bug, Lygocoris rugicollis
Mealy apple aphid
- Leaves of the apple tree turn yellowish, later they turn brown to black, leaves cripple, curl up and can fall off prematurely
- Shoots are twisted and compressed
- Fruits remain small, wrinkled and blotchy
- Then cut off heavily infested shoots and use approved pesticides if there are large numbers
Stress-Related Causes
If diseases and pests can be ruled out as the cause of leaf damage, stress or physiological impairments can lead to discoloration, browning or premature leaf fall. Several factors can stress the apple tree:
- Planting in summer heat and drought
- Dry root ball due to lack of water supply
- Too hard or stony ground
- Changing weather conditions
- Young or newly planted apple trees are particularly susceptible
- Because roots are still relatively small
- Leaves are not yet sufficiently supplied with moisture and nutrients
- Tree sheds leaves to protect and balance
Countermeasures are usually not necessary. Because once the tree is rooted, it usually recovers relatively quickly. The situation is different when the sap balance is disturbed due to root damage, for example by voles, which causes the leaves to turn yellow. To protect against these rodents, you can bring a sufficiently large wire mesh into the ground when planting and place the tree in there.