Sooty blotch and fly speck are two distinct diseases of apple but usually occur together. The diseases occur sporadically in conventionally sprayed orchards but are prevalent and can cause serious losses in wet seasons in organic orchards or where fungicide use is reduced.
Both diseases are caused by fungal disease complexes rather than individual fungal species and cause characteristic symptoms of a sooty-like discolouration (sooty blotch) or black shiny dot blemishes (fly speck) on near mature fruit and, although superficial, this causes fruit to be downgraded and reduced in value.
The life cycle and epidemiology of these fungi involves overwintering on apple twigs and on many hedgerow and wild tree species. In spring spores produced on apple twigs and hedgerow hosts spread in wind and rain to infect apple twigs and subsequently infect fruit from early summer to harvest. Secondary spread from these early colonies occurs throughout the summer. Growth of these fungi is favoured by high humidity and temperatures from 18-27 degrees C. However, visual symptoms on fruit do not appear until 3-6 weeks after initial colonisation.