Last updated on October 23rd, 2023 at 08:30 pm
Apples are healthy and from your own tree they still taste best. When looking for the right apple variety, you can choose between different flavors, colorings and harvest times. In some cases, you can even do without a pollinator variety. But for all the joy of self-harvested fruit, apple trees can also be affected by a disease or pest infestation. Yellow, blotchy leaves or premature leaf drop may indicate this.
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Causes of leaf damage to the apple tree
If the apple tree shows yellow, brown spotted leaves or loses its foliage early, this can have several causes. Usually these symptoms occur together with others, so 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 either.
Diseases
Apple scab
Apple scab, a disease caused by the tubular fungus Venturia inaequalis, is one of the most important apple tree diseases. High temperatures and humidity in spring or prolonged leaf wetness favor an infestation. However, small brown spots on and under the foliage leaves, which slowly grow larger and converge, can also be signs of an infestation. In early infestation often only the tips of the sepals are affected, later usually the whole leaf. Then they die, the tree becomes bare.
Control
Since this fungus overwinters in the foliage, fallen leaves should be completely removed from the ground. Because otherwise a new infestation is pre-programmed. To inhibit the development of the fungus, a layer of mulch on the tree disc can be helpful, but not directly up to the trunk and no bark mulch. Likewise, the crown should be thinned out by regular pruning in the winter so that the interior of the crown is better ventilated.
Tip: To counteract diseases in general, choose resistant varieties when buying.
- Collar rot
- Collar rot caused by fungi of the genus Phytophthora.
- Trees show reduced growth
- Foliage initially yellowish, later reddish in color
- tree loses foliage prematurely
- Fruits remain smaller, are more intensely colored (emergency ripening)
- Individual branches die
- For disease progresses slowly
- Apple tree dies within two to four years
Control
In case of light infestation, cut off affected parts of the plant and treat the resulting cuts with an agent against fruit tree canker. But if the collar rot is already advanced, the apple tree usually has to be cut down. Nevertheless, as a preventive measure, care should be taken to use resistant varieties, avoid injury to the grafting point and remove fallen fruit regularly. In addition, the tree disc should be covered with compost or mulch, leaving about 10 cm free around the trunk.
- Marssonina leaf spot disease
- Occurs around July and August, during prolonged periods of rainfall.
- Fungus Diplocarpon mali overwinters in the fallen leaves
- Infects leaves at the beginning of the flowering period
- Permanently wet foliage and temperatures above 20 °C favor an infestation
- Infested foliage is mottled brown
- Spots run into each other over time
- Later yellow discoloration over large areas
- Partially necrotic mottling with red-purple bordered spots
Fungicides that are also used to control apple scab and apple powdery mildew are suitable for control. Regular pruning of fruit trees ensures that all areas are well ventilated.
Tip: Careful removal of fallen leaves in the fall reduces the risk of re-infestation.
Pest infestation
Pest infestations occur primarily in the spring and summer. Some pests use the apple tree as a breeding ground for their offspring, which then feed on young leaves, shoots and flower buds after the winter. Several pests are possible causes of the above-mentioned leaf damage.
Apple rust mite
Indications of apple rust mite initially yellowish and later rusty-brown spotted undersides of leaves.
upper leaf surface is dull and lackluster
As a countermeasure, remove infested branches and use natural predators such as predatory mites
Do not dispose of cuttings in the compost
Fruit tree spider mite
- causes fine whitish leaf spots
- Foliage later turns dull, silvery bronze color, tree loses foliage early
- Negative effects on flower bud set and fruit color
- Control by natural enemies such as lacewings, ladybugs and spiders.
- Use of chemical sprays in spring only in exceptional cases, also kill the mites’ natural enemies
Apple bug
Small holes and brown leaf spots can indicate the presence of apple bug
Growth of young shoots is interrupted, fruits show corky spots
Pests can be shaken off early in the morning, minimizing infestation
Use insecticides only when infestations are severe.
- Mealy apple aphid
- Leaves of the apple tree turn yellowish, later brown to black discoloration appears, leaves are crippled, curl up and can fall off early
- shoots are twisted and compressed
- Fruits remain small, wrinkled and are blotchy
- Then cut off heavily infested shoots and use approved plant protection products in the event of mass occurrence.
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 drop. Several factors can stress the apple tree:
- Planting during summer heat and drought.
- Dried out root ball due to lack of water supply
- Too firm or stony soil
- Changeable weather conditions
- Young or freshly 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 itself and to compensate
Countermeasures are usually not necessary. This is because once the tree is rooted, it usually recovers relatively quickly. The situation is different if there is a disturbance of the sap balance due to root damage, for example by voles, which results in yellowing of the leaves. To protect against these rodents, when planting, you can put a sufficiently large wire mesh with in the ground and put the tree there.