Sooty blotch and flyspeck (SBFS) are two of the most important summer diseases of apple in New York. The diseases do not result in direct losses in yield, but rather they cause a reduction in fruit quality, which can lead to economic loss due to downgrading in fresh market fruit. Losses can exceed 25%, especially in warm humid climates such as those encountered in southeastern NY, southern New England, and the mid-Atlantic and southern United Stats.
Until recently, sooty blotch was thought to be caused by the fungus Gloeodes pomigena. However, recent studies have shown that sooty blotch is a disease that can be caused by more than 20 different fungi, not all of which are present in all geographical areas. Flyspeck is now sometimes considered part of the sooty blotch complex, but most of the classical flyspeck lesions in Northeastern United States are caused by the fungus Schizothyrium pomi (= Zygophiala jamaicensis).
Symptoms: Sooty blotch appears as various shades of olive-green on the surface of the fruit. Colonies range in shape from nearly circular with distinct margins to rather large, amorphous blotches with diffuse margins. The variation in shapes and color can be attributed to the interaction between the different fungi causing the disease and environmental conditions, specifically temperature and relative humidity.
Flyspeck appears as distinct groupings of shiny, black fungal bodies (called thyriothecia) on the surface of the fruit. The number of thyriothecia associated with a single infection ranges from a few to over fifty. Although flyspeck thyriothecia appear to exist individually, close examination reveals mycelium connecting the individual structures.
For both flyspeck and sooty blotch, the causal fungi grow only within the wax cuticle of the fruit and are quite superficial. Rubbing the fruit with a cloth will often be enough to “clean-up” an apple that is only lightly affected.
Disease Cycle: The details for the life cycles of the sooty blotch fungi have not been fully elucidated. However, the disease cycle is assumed to be similar to that described when sooty blotch was assumed to be caused by Gloeodes pomigena. The fungi overwinter on infected twigs on apple and on its numerous wild hosts. Conidia are formed in late spring and early summer and dispersed to developing fruit by wind a splashing rain. Fruit infection typically occurs from late-April to mid-May in the southeastern United States and in June in the northern and northeastern United States. The first symptoms are generally apparent 20 to 25 days after infection, but can be visible in 8 to 12 days under optimal conditions.
Flyspeck overwinters as thyriothecia on apple twigs, culled apple fruit, and on numerous wild hosts. Ascospores mature and are discharged shortly after bloom and initiate infection (Lerner, 1999; Williamson & Sutton, 2000). The time of discharge varies from region to region and in relation to environmental factors. Symptoms are visible 10-12 days after infection under optimal conditions, but symptoms in the field usually require more than 30 days, and sometimes up to 60 days, of incubation before they become visible. Initial infections will give rise to conidia which initiate secondary infection throughout the remainder of the season.
Numerous observations in the field have shown that warm and wet or humid conditions are needed for the development of flyspeck disease. Laboratory studies have shown that conidia can germinate within the range of 8-24 C, colony development occurs over the range 5-28 C, and spore production readily occurs between 12-24 C (Ocamb-Basu et al., 1988a; Williamson & Sutton, 2000). All three processes require that the relative humidity exceed 96%. The development of asci was initiated at temperatures between 4-6 C and ascospore maturation occurred at various temperatures between 9 and 21 C. Again, both processes require a high relative humidity.
Fruit Quarterly
2007 Timing Summer Fungicides to Control Flyspeck Disease on Apples
Scaffolds
2014 Controlling Summer Diseases on Apples
2005 Timing Sprays for Flyspeck and Sooty Blotch (download) /(web)
