Apple tree problems: frequently asked questions
Apples are easy to grow, productive, and there are cultivars, shapes and sizes for every garden. They can be susceptible to a range of damaging invertebrates, diseases and disorders, but in most cases action can be taken to prevent or control the problem. Susceptibility to the problems differs between cultivars – you would be very unlucky to have a tree that suffers from all of the problems listed below! Here we give answers to many of the common problems encountered. They are grouped by the area of the tree affected: shoots; leaves and flowers.
- Apple scab
- Brown rot
- Honey fungus
- Poor fruiting
Take a look at some of the common problems you might encounter on an apple tree.
Question: My tree looks as though it is dying. I dug down to look at the roots, and found that many of them were soft and brown. The thicker ones were discoloured under the bark. What has happened?
- Root decay in apple trees can be the result of an attack by a root disease. The two found most commonly are honey fungus and Phytophthora root rot. Both of these can also affect the base of the stem
- Root decay can also be caused by waterlogging. Be aware that Phytophthora root rot is itself favoured by waterlogged conditions
- Root death in container-grown trees can sometimes be the result of hard frosts – the roots can be given some protection by wrapping the container with bubble wrap
Stems and branches
Question: The shoots/twigs/branches of my apple tree are dying back. What could be wrong?
Branch dieback can be another symptom of the root problems described above, as the tree struggles to take up water through its poorly-functioning root system
If the dieback is accompanied by areas of sunken, dead bark then the likely cause is apple canker. This disease can affect twigs, branches and even the main trunk
- If the dead branches have numerous pinhead-sized, raised, coral-pink pustules on the surface then coral spot is involved. The fungus often attacks trees already weakened or dying back due to other problems
- Dieback of numerous shoots in late spring, with the leaves shrivelling and turning brown after flowering, is usually the result of the fungal disease blossom wilt. Dieback due to blossom wilt rarely progresses back more than 15-30cm (6in-1ft). Shoot dieback at this time can also be caused by the bacterial disease fireblight, but this is much less common. Dieback due to fireblight often spreads further down the shoot than blossom wilt – it can work its way back into the main branches
- If branch dieback is preceded by the leaves taking on a silver colouration, then the most likely cause is silver leaf disease. Check for the characteristic wood staining within the affected branch.
Question: The shoots/twigs/branches of my apple tree are covered with a grey-coloured crusty growth. Is it harmful?
No, this is a harmless lichen. A build up of lichen near the shoot tips can suggest your apple tree is low in vigour. In which case, concentrate on some winter pruning and spring/summer feeding to promote more active growth.
Question: My tree has developed lumpy outgrowths on the bark, which are covered with a white, fluffy substance. Is this a disease?
No, it is an insect called woolly aphid. The brown-black aphids secrete the white wax as a form of defence.
Question: What is the white powdery growth present on the leaves of my tree?
This is the disease powdery mildew. Heavy infection can reduce the vigour of the tree.
Question: The leaves of my tree have developed greenish-black spots and blotches, and are falling early. What is wrong?
Your tree is affected by the disease apple scab. This disease can also attack the fruit (see below).
Question: Why have the leaves on one branch of my tree turned a silvery colour?
The most likely cause is a disease called silver leaf, which can also cause branch dieback.
Question: The leaves on the young shoots of my apple tree are curled and sticky. What has caused this?
The shoots are infested by aphids. A number of species can affect apple trees – some species leave the tree in summer to find other host plants, whereas others remain on the tree. The sticky substance is honeydew produced by the aphids, and this can lead to the growth of sooty moulds. The uncommon rosy leaf-curling apple aphid causes leaves to become distorted and red. Rosy apple aphid is a frequent pest and causes yellowish green curled leaves; it can also affect the fruit (see below).
Question: What is eating the leaves of my tree?
The caterpillars of a number of moth species will eat the leaves of apple trees.
- Winter moth caterpillars are particularly troublesome between bud burst and late May as they will also eat blossoms and damage young fruitlets
- Caterpillars of many tortrix moths protect themselves when feeding by webbing leaves together with silken threads. Some species of tortrix can also damage the fruit
- The caterpillars of codling moth (see below), a type of tortrix, feed exclusively within the fruit
Distorted young leaves full of small holes may have been damaged by capsid bugs.
Question: What are the narrow, curvy, brown or white lines on the leaves of my tree?
These are mines produced by caterpillars of the apple leaf-mining moth. No significant damage is done to the tree, so no control measures are required.
Question: Some of the fruit on my tree has gone brown and rotten, and is covered in light brown pustules. What is the cause?
The fruit is affected by the fungal disease brown rot.
Question: What disease has caused the brown, scabby lesions and cracks on the fruit?
These are the fruit symptoms of apple scab.
Question: Why do some of my fruit have black marks on the outside?
The fruit may have been affected by the fungi causing blemish diseases known as sooty blotch and flyspeck.
Question: Fruits are falling from my tree and have been eaten inside. Which pest is responsible?
The two common culprits are apple sawfly and codling moth.
- Fruit affected by the larvae of apple sawfly often fall from the tree in June or early July. Sometimes sawfly larvae feed only beneath the skin of the young fruitlet rather than burrowing into the core – these fruit usually survive but have a long ribbon-like scar on the exterior by the time the fruit is ripe
- Those attacked by codling moth don’t fall until the fruit is ripe
Question: Why are some fruit on my tree bumpy and distorted?
If the fruits are undersized, with a pinched appearance at the eye end, it is likely that the affected fruits were infested earlier by rosy apple aphids. If there are isolated, corky bumps then capsid bugs may have been responsible.
Question: The fruits from my tree have brown specks inside and a bitter taste. What has gone wrong?
This is a disorder known as bitter pit, caused by low calcium levels in the developing fruit.
Question: Why do large numbers of fruit often fall from my tree in mid-summer?
The most common cause is a phenomenon known as the June drop (although it can occur in July as well as June). This is a natural process, during which the tree reduces its total crop to a level whereby the remaining fruit can be adequately supplied with nutrients until they are mature. If the initial fruit set has been poor (see below) then the June drop will be reduced. The extent of the drop can also vary according to the cultivar and the age of the tree (young trees are more commonly affected).
Some insects and diseases can cause fruit drop, as can adverse growing conditions such as severe drought.
Question: My tree has hardly any fruit! What has gone wrong?
Possibly causes of unproductive fruit trees include:
- Poor weather restricting the activity of pollinating insects during flowering
- Frost damage to the flowers
- Birds (e.g. bullfinches) eating the flowers
- Lack of a pollinating partner - you may need to plant another apple cultivar
- Biennial bearing – some trees have a habit of alternating a year of heavy cropping with few or no fruit the following year
- Young tree – it may take a few years for fruiting to start (this can vary according to the cultivar and the rootstock on which it is growing)
- Poor pruning technique
- Poor growing conditions, e.g. drought, excess shade, lack of nutrients
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