Top fruit diseases frequently affect several different types of top fruit trees, and often have common causes, effects and solutions. Where diseases are particular to an individual top fruit, details will be given in the relevant variety section.
APPLE AND PEAR CANKER.
Apple Canker, and the related but not so common Pear Canker, are most prevalent in the colder and wetter areas of the UK. It is not surprising therefore that this disease is a real problem for growers of Apples and Pears in the North-west of the UK. Cankers are caused by a fungus whose spores are spread by the wind, particularly during the Spring. The spores gain entry to the tree bark through damaged areas, which could have been caused by physical damage caused by unprotected pruning, branches rubbing together, scab infection, insects or frost damage.
The disease causes cankers which are areas of shrunken bark, often beside buds or damaged areas. The area of the canker steadily expands, changes colour, shrinks and cracks. Swelling can also take place and the wood under the bark dies. When eventually the dead wood encircles the twig or branch, it dies. In the worst case scenarios, the cankers attack the main trunk of the tree.
Diseased twigs and branches must be cut out and the debris burnt as soon as it is spotted. The cut ends of the branches must be immediately sealed with a proprietary sealing compound.
If the canker is on the main trunk of the tree and is still quite small, you could try cutting and gouging out the area of the canker and the dead bark and wood underneath. You will need to extend the area until there is absolutely no sign of diseased or discoloured timber left. Again seal the wound. In all cases make sure that you only use sterilised secateurs and saws before each cut as you could quite easily transfer the canker spores to another part of the tree or even a different tree. Experts suggest using boiling water for this.
To counter canker disease consider a spraying program using Bordeaux mixture and apply immediately after picking the fruit and after half the leaves have fallen.
Other measures suggested by experts to improve the local environment of the tree include:-
Improve the drainage by either planting the tree on a raised area of soil, or alternatively dig a trench about a metre radius from the tree trunk to drain the local area of the tree.
Improve airflow through and around the tree, by pruning to keep the centre of the tree open. Remove weeds around and under the tree.
This is a different disease from the apple canker described above, as it affects all stone fruit trees. You are likely to first spot the tell-tale cankers in the Spring, when they start to ooze patches of gum on the bark and the affected branches die back, and any leaves on the affected branches are likely to be small, yellow and shrivel. As soon as you see signs of die-back of the branches, you should cut off the branch with sterilised tools, seal the would with a protective paint, and burn the diseased branches. Do not confuse this condition with “gummosis”, which is when the gum appears on the bark of healthy tissue. This gum is the tree’s response to seal over physical damage to the bark. You may also see the gum if you cut off a branch. Preventative treatment consists of spraying the tree in August, October and the Spring, with Bordeaux mixture.
APPLE and PEAR SCAB.
This disease usually shows itself as black or “corky” spots on fruit, and later the fruit can become distorted, misshapen or cracked. However, it also damages the foliage and young shoots and may be another way that canker spores gain access to the tree.
Scab is most likely to occur if the Spring weather is cloudy and wet, especially during the flowering period.
Remedial measures to combat this disease include raking up and burning the old apple leaves to remove one source of the spores of the disease.
Spraying of the trees should be carried out in the Spring with mycloobutanil.
Brown rot is caused by a fungus and can cause a lot of damage on Apples, Pears, Plums, Peaches and Nectarines. It is spread by birds, wind and the rain, and there is no chemical treatment. The affected fruits start to go brown and soft with obvious spores on the surface of the fruit. The disease will spread quickly to any touching fruits. Most of the diseased fruits fall off the tree, but sometimes the fruits mummify and will even stay on the tree over-winter, being a reservoir of disease. The only treatment to limit the spread of brown rot is to carry out regular inspections of your fruit trees, removing and destroying any diseased fruits, particularly in wet weather when the fruit are almost ripe. Make sure that you remove any fallen diseased fruit. Never try to store diseased fruit and regularly inspect and remove any stored fruits that show signs of disease.