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Shot Hole Disease (Coryneum Blight)-  HOSTS: Stone fruits (peaches,
apricot, plums, sweet cherries). DESCRIPTION:
Symptoms
appear on new leaves as small reddish spots that enlarge and become
purple with a white center. These spots then drop out of the leaf,
leaving a "shot hole" appearance. On fruit, dark colored lesions
develop and eventually become corky, rough, and scab-like. Infections
on maturing fruit are sunken, up to ½ inch long, brown spots,
which cause the fruit skin to crack. The fungus can kill dormant buds,
blossom buds, and small twigs. LIFE
CYCLE: The shot
hole fungus over winters on dormant infected leaf buds, blossom buds
and
small twig cankers, but not on old infected leaves. Spores are produced
in the early spring; bud and twig lesions may continue to produce
spores for two to three years. Wind disseminated spores require free
water droplets on the fruit, leaf, or twig surface in order to
germinate and cause infection. Temperatures of
70-80° F are optimum
for infections; lesions can develop at 45° F if 20 hours of
continuous moisture occur. It takes from two to five days for a
visible
lesion to appear after infection. CONTROLS:Cultural: Prune out dead branches and twigs. Mineral: Protect with an oil-free lime sulfur spray as buds break in the spring. Daconil is the "hard" pesticide option if infection periods are severe. If weather is wet and temperatures are >60° F., protect newly expanded leaves with sulfur or another fungicide. NOTE: Do not use sulfur on apricots. |
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