University of Vermont Extension
Department of Plant and Soil Science
TREE FRUIT DISEASES
Dr. Leonard Perry, Extension
University of Vermont
Apple scab, brown rot, and black knot are
common fungal diseases on tree fruits in New England. Being ready for
these if you have crabapples,
flowering cherries, and fruit trees, and knowing cultural controls,
you have better fruit with the least harm to the environment. A New
website of Extension services (pronewengland.org) provides some photos,
information, and further resources on these and other garden problems.
Apple scab disease causes velvety
brown lesions on apple and crabapple leaves in spring and summer. It
causes corky scars and splitting on fruit
in late summer and fall. There are
similar scab diseases which attack peaches and pears. Watch for the
most apple scab after rainy,
cool spring weather.
Since infected leaves drop and produce
spores the following spring, which spread the infection, one method of
is to keep such leaves raked in the fall and destroyed. There are
fungicides that may be used, but if
doing so be sure and follow all label directions. Perhaps the best
control if you are
considering planting apple trees, or replacing old ones, is to plant
resistant to this disease. These, and
highly resistant crabapples, can be found in a Cornell University
Brown rot disease kills blossoms of
peach, cherry, plum, and other stone fruits in spring. It
causes a soft, watery rot on fruits in summer.
These infected fruits eventually dry (called
“mummies”) and produce spores for the
following spring. So one of the best
controls is to prune such dried fruits from trees and burn or bury them
deeply. Insects create wounds on fruits
for the disease to enter, so controlling insects in summer helps to
damage. Since most stone fruits are
susceptible to brown rot to some degree, fungicides often have to be
optimum control. Check your local garden
store for these, and follow all label directions.
Black knot disease is found on plum and
cherry trees. Spring infections lead to
an inconspicuous swelling on current year growth during the fall.
These swellings turn into green and soft
knots the following spring. By the
second fall these knots turn hard and black, from a half inch to over a
long. Since this disease takes so long
to develop, it is often overlooked until it is hard to manage.
Prune out branches with such knots during
winter, before spring bud break. Make
sure to cut the branch at least six inches below where you see the
order to remove all the disease. Remove
such knots in any wild plums or cherries that may be nearby as well.
Pruning, planting resistant varieties, and
not planting trees on sites with the problem (abandoned orchard or
wild trees adjacent) usually will keep this disease under control
Other diseases to be aware of on apples
include cedar-apple rust, fireblight, and powdery mildew. Other
diseases on stone fruits include
botrytis blight, brown rot, cytospora canker, and powdery mildew. More
on all these can be found at the above
Cornell factsheet website.
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