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.
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
blotch on apples. Photo from the Univeristy of Vermont Extension.
is characterized by clusters of 10 to 50 sharply defined, black,
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.
on apple. Photo from the West Virginia University Extension.
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.
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.
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.
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.
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.
K.D. Hickey, K.S. Yoder, and A. R. Biggs, West Virginia University