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.