The first thing to assess when you think that you have a diseased apple tree, is whether in fact your apple tree is actually 'diseased' or is affected by a 'pest'! A pest is a living insect or mite, whereas a disease is normally a fungal infection. It can also be a virus.
Basically, if it has legs - it is a pest. An insect of sorts that can be treated with an insecticide. Insecticides are no use whatever in treating diseases. (However, some diseases are spread by insects, so there is sometimes a case for treating a disease bearing insect!) Some pest look like diseases, which does not help. Woolly aphid in particular, is often confused as a fungus because of its cotton wool appearance.
Fortunately, there are not too many diseases that commonly affect apple trees, and the identification can normally be positive. Most of the diseases on Apple Trees are caused by fungus, and can be controlled by fungicides or other physical control.
The most common disease affecting apple trees is some form of Canker or other. The image shows an early attack, which can develop into large lumpy growths - affecting the tree quite severely unless treated.
Apple Scab is a fungal disease, and normally appears in the later part of autumn, or early in spring. It shows as brown or black pimples on leaves, and ultimately to the fruit of the apple tree.
It is spread by wind, so can easily take hold if not checked in early stages. Leaves will not stay on the tree, and signs on the apples are maturing unevenly - eventually cracking and spoiling.
The scab looks as its name sounds!
Prune any affected areas and burn the debris. Affected fruit should not be stored. There can be lasting damage to the apple tree from Apple Scab Disease.
The name is very descriptive of this disease of apple trees. It is a disease that also affects many other garden plants.
It is normally to be seen in periods of high humidity, but thrives in hot dry conditions also.
If left untreated, Powdery Mildew Disease will cause severe weakening of the tree, starting with young growth. This will result in the death of the terminal bud of the twig.
A strong healthy tree will survive the disease without too much ill effect. Aim for good air circulation between the branches, and control with a fungicide or sulphur spray.
Fire Blight Disease is again aptly named, for the apple tree will look as though a fire has been started nearby - scorching the foliage up one side of the tree.
It is a serious disease that can also affect many other plants of the same genus as Apples - The Rose family. (Pyracantha, Hawthorn etc are also affected.)
Affected young shoots will wither and die - as will any flowers.
Prune back hard, any affected branches and burn the debris.
Black Rot Disease will be visible on mature fruit - just as they are nearly ready to harvest - typical!
Often, the apple has already been wounded by some physical force or other. This will include bruising damage as a result of windy conditions.
The disease is first noticed as small brown spots on the apple fruit, which will then grow - turning first dark brown and then black!
If caught early enough, then the fruit can be treated with a sulphur spray.
It can spread to the bark of the tree and will overwinter - ready to affect the tree in the spring growing season. A good fungicidal spray in early winter will help this and other fungal diseases of apple trees.