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These blemish diseases are caused by unrelated fungi, but both result in dark fungal growth on the surface of the fruit. Apples are affected most commonly, but the fungi may also be found on pears, plums and citrus fruit. Eating or cooking quality is not affected. The diseases are most common in wet summers.
Sooty blotch and fly speck of apples
Sooty blotch and flyspeck are fungal blemish diseases of fruit. The diseases are sometimes found together on the same fruit, as they are favoured by very similar weather conditions, but they can be distinguished from each other by their symptoms.
The fungal growth develops on the fruit surface, and can be rubbed off (although sooty blotch may leave a discolouration behind).
N.B. Sooty blotch is caused by a different fungus from those responsible for another problem known as sooty mould. Sooty mould (caused mainly by species of Alternaria and Cladosporium) is another type of superficial, dark fungal growth, found commonly on the aerial parts of plants affected by sap-sucking pests such as aphids and whiteflies.
You may see the following symptoms:
There are no fungicides available to home gardeners for use against sooty blotch and flyspeck.
Both of these diseases are favoured by warm, wet weather conditions. In addition to the tree fruit listed, the fungi can affect the leaves, twigs and fruit of a wide range of other woody and herbaceous plants. The effect of the fungal growth on most of these other hosts is totally insignificant, although both sooty blotch and flyspeck can sometimes cause blemish problems on the leaves of orchids, and the flyspeck fungus also causes a foliar disease of Dianthus known as greasy blotch.
The fungi overwinter on the twigs of the fruit trees, and on twigs, stems and leaves of other woody and herbaceous plants in hedgerows, ditches, etc. Spores are produced in spring and early summer and reach the developing fruit. Further spores are produced during the summer from the growth on the fruit to continue the spread of the problem.
The growth of the flyspeck fungus develops entirely on the surface of the fruit. The sooty blotch fungus can sometimes penetrate just below the cuticle, which is why a discoloured patch often remains after the surface growth is removed.
ApplesApple scab and pear scabBitter pit in applesBrown rotDisposing of diseased materialFruit: storingPears
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