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Coryneum Blight (Shot Hole)
Causal Agent: Wilsonomyces carpophilus
Coryneum blight is a fungus disease of apricots, peaches, and cherries. Fruit
symptoms are most severe when there is frequent wet weather at husk fall. On
peach, apricot and cherry fruit, coryneum blight causes small reddish-brown to
purple spots, some of which appear scabby later in the season. On peach twigs,
small, dark, circular to elliptical spots develop, some becoming gummy. Twig
infections on apricots and cherries are not common, although bud infections
occur on apricots. Shotholes in leaves are common on cherries and may also
occur on peaches and apricots.
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Coryneum blight on apricot |
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Coryneum blight on cherry
Photo courtesy Agriculture & Agri-Food Canada |
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Coryneum blight on peach |
Cultural Control
Prune out infected twigs in the dormant season.
Chemical Control
- To prevent twig and bud infections, apply fixed copper fungicide (not
copper sulphate) after harvest on peaches, or September 1 (before fall
rains) on apricots and cherries. This spray also helps to control peach leaf
curl.
Fall applications of fixed copper prevent the formation of new twig
cankers but WILL NOT remove existing cankers. A spring fungicide application
is necessary to prevent fruit infections in orchards where coryneum has been
a problem. In such cases, an aggressive program is required for a minimum of
three years in order to minimize the chance of fruit infections from old
twig cankers.
- To prevent fruit infections, follow up the autumn treatment with a spray
of ferbam or ziram on peaches and apricots as soon as most of the husks have
dropped so that the fruitlets will be completely covered by the spray.
Application of ferbam should not be delayed once husk fall stage is reached,
because later application can cause an unsightly deposit on the fruit.
- Extra care must be taken to control coryneum blight when over-tree
sprinklers are used.
February 2004
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