Sooty blotch (Peltaster fructicola, Geastrumia polystigmatus, Leptodontium elatus) and flyspeck, (Zygophiala jamaicensis) are surface blemish diseases that commonly appear together on apple or pear in late summer and fall. Although these diseases may shorten the storage life of fruit due to increased water loss, they do not cause decay. The apples are still fine to eat--losses are attributable to unacceptable appearance. Homeowners who wish to avoid the use of fungicides may still eat the applies. Wiping the apples with a soft cloth will remove most traces of the disease. During wet growing seasons, losses of 25 percent or more are commonly found even in orchards treated with fungicides.

Symptoms:

Sooty blotch appears as sooty smudges or olive-green spots on mature fruit. Individual spots or smudges vary from discreet circular colonies to large lesions with diffused margins. Different colony appearances are attributable to different fungal pathogens which comprise the disease complex.

Sooty blotch on apples. Photo from the Univeristy of Vermont Extension.

Flyspeck is characterized by clusters of 10 to 50 sharply defined, black, shiny specks on the fruit surface. These superficial colonies are round to irregular and usually measure 1/16 to 1 inch (2-25 mm) in diameter. The individual dots or specks are fruiting structures in which spores are formed which cause secondary spread.

Flyspeck on apple. Photo from the West Virginia University Extension.

Although these diseases may appear separately, they are commonly found together on the same fruit. Typically fruit symptoms are observed by the first of July and become more evident as the season progresses. There are no significant differences among apple cultivars in susceptibility to these diseases, but symptoms are more apparent on yellow, green or light colored fruit. Fruits of apple and pear with thicker cuticles appear to be more severely affected.

Disease Cycle:

These fungi are commonly found on the stem surfaces of many woody plants, including apple shoots. Infections may occur on fruit as early as two to three weeks after petal fall, and are highly favored by frequent rain periods and poor drying conditions. Mycelial growth that forms the sooty blotches can occur in the absence of free water at relative humidity greater than 90 percent. Symptom development of both diseases is relatively slow, typically requiring 20 to 25 days in the orchard, but may occur in 8 to 12 days under optimum conditions. Optimum conditions for conidial production for the flyspeck pathogen are 60 to 70 degrees F (16-21 degrees C) and relative humidity greater than 96 percent.

Monitoring:

At midseason, observe 25 fruit in the interior canopy of sample trees. Symptoms are more likely to be found in poorly pruned trees in the wetter, foggy, slow-drying areas of an orchard. Expect first symptom expression by early to mid-July.

Continue to observe 25 fruit in the interior canopy of sample trees. Fungicides should be applied to fresh fruit showing any infections. Presence of these diseases is a good indicator that fungicide surface residues are lacking or very low, and signals potential need for treatment to control these diseases or the decay producing fungal pathogens. Note that many fungicides have a 90 days to harvest requirement.

Management:

Removing reservoir hosts, especially brambles, from the orchard and surrounding hedgerows helps reduce the amount of inoculum from external sources, but in wet years this practice alone may not be adequate for disease control. Some cultural practices may help prevent the diseases and/or reduce the severity of sooty blotch and flyspeck. These include dormant and summer pruning to open up the tree canopy and thinning to separate fruit clusters. In addition to facilitating the drying of fruit after rain or dew, these practices favor better spray coverage and improve fruit quality. Both diseases are difficult to control in orchards with restricted air movement.

Adapted from K.D. Hickey, K.S. Yoder, and A. R. Biggs, West Virginia University Extension, 2000