Advice
RHS Help & Advice
Apple canker
Plants affected
Apples (Malus), pears (Pyrus), rowan (Sorbus aucuparia) and occasionally beech (Fagus), ash (Fraxinus) and other broad-leaved trees. Mulberries (Morus) are attacked by a similar disease, but treated in the same way.
Symptoms
Early symptoms include dead, leafless twigs or shoots bearing small sickly-looking leaves. Closer inspection reveals the cankers: sunken, swollen, distorted and cracked areas of bark that may be dotted with small white or red pustules. The causal fungus also sometimes infects fruit, resulting in a rot on the tree or in storage.
Cause
This is one of the commonest and most serious diseases of apples and pears. The cause is the fungus Nectria galligena. Infection occurs by spores penetrating through leaf, bud-scale and fruit scars, or wounds caused by pruning, frost damage, scab or possibly woolly aphids. Wherever possible, try to avoid this type of injury or infestation, especially on young trees. Trees suffering from some other form of stress, waterlogging or nutrient deficiency for example, are more prone to the disease.
Non-chemical control
- Prune out cankers on small branches and twigs, making sure that you cut back well into healthy wood that shows no sign of staining on the cut surface. Avoid pruning in wet weather.
- On larger branches and trunks you can remove the canker with a knife or wood chisel. All discoloured, diseased bark must be pared away leaving only pale, healthy tissue.
- Collect and destroy all infected tissue and pruned-out areas either by burning or sealing in a plastic bag and putting in the refuse bin.
- Apply canker paint (e.g. Vitax Medo) to the cut areas.
- The varieties ‘Cox’s Orange Pippin’, ‘Lord Suffield’, ‘James Grieve’, ‘Ribston Pippin’, ‘Worcester Pearmain’, ‘Ellison’s Orange’ and ‘Spartan’ are susceptible. If canker is a particular problem in your area, consider choosing ‘Grenadier, ‘Annie Elizabeth’, ‘Laxton’s Superb’, ‘Newton Wonder’, ‘Lane’s Prince Albert’ or ‘Winston’, which are resistant.
Chemical control
- Applications of the copper fungicide Bordeaux Mixture (Vitax) can limit the spread of the disease. Make two applications in the autumn, one directly after harvest and the second when about half the leaves have fallen.
- Fungicidal sprays used against apple scab (myclobutanil (e.g. Systhane Fungus Fighter) or mancozeb (Dithane 945)) or powdery mildew (myclobutanil), give incidental control of canker. Control woolly aphid (the role of woolly aphid in canker development is unclear, but it is damaging in any case).