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University
of Rhode Island GreenShare Factsheets
Apple
Diseases: Sooty Blotch and Flyspeck
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.
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.
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.
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.
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.
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.
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
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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