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Coryneum blight

Coryneum blight

Posted - Oct. 22, 2004 at 8:36 p.m.



This archived news story is available only for your personal, non-commercial use. Information in the story may be outdated or superseded by additional information. Reading or replaying the story in its archived form does not constitute a republication of the story.

Larry Sagers Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved

With the sudden change in the weather and the very welcome rain, plan on treating your peaches for Coryneum blight or shothole blight.

This is a fungal disease affecting peach, apricot, nectarine, and cherry. It may infect the leaves, fruit, buds, blossoms and twigs of susceptible trees.

The fungus overwinters in twig cankers and blighted buds. The spores form in the buds and cankers and are spread by fall and spring rains, and infect leaf scars produced when leaves drop in the fall.

Spores also move by rain to leaf or flower buds and remain under the bud scales until ready to germinate condition are right. In the spring, these spores infect the swollen buds, and kill the bud or cause blossom blight, or "shot-hole" symptoms in the leaves.

Cankers develop on new wood and can girdle and kill developing buds and twigs. Spores produced on twig cankers in the spring infect susceptible plant tissue during rainy periods.

Bud and twig infections commonly cause of damage to peaches. Twig infections create cankers that often surround leaf or flower buds. The cankers turn purple or brown in color and are slightly sunken. They enlarge and grow together to girdle a branch or twig and kill it.

Gumming is common around infected buds and cankers. Leaf infections appear as small tan spots on young leaves. These later turn brown with purple borders. The spots eventually drop out of the leaf, giving the "shot-hole" symptoms. Leaf infections in Utah are more frequent on peach than apricot, unless the weather is very wet.

Fruit infections occur infrequently on peach but occur almost every year on susceptible varieties of apricot. Infections are small reddish-brown spots with light centers on immature fruits. On apricot fruit, the spots become rough and hard, with dry, corky areas in the fruit underneath the spots.

The spots may grow together then produce large, irregular, leathery patches with cracking and gumming. The fruit, though spotted, can still be used.

Fruit infections are reduced by cleaning up the orchard and protective sprays. Sanitation is important in reducing inoculum in wet years. During spring pruning, remove all obviously diseased wood and destroy it.

Avoid sprinkling the leaves during irrigation. Apply protective fungicide sprays if you have frequent spring and fall rains. Homeowners can protect backyard trees by carefully pruning out cankers, controlling sprinkler irrigation, and apply one of the following chemicals just after leaf drop in the fall to protect against bud infections. Treat trees with Bordeaux, chlorothalonil (Daconil), captan or fixed coppers.

Combine dormant oil with fixed coppers as stickers. Do not use copper sprays in the spring after trees leaf out, as they may burn the leaves.

Young leaves and fruit (especially apricots) require protective sprays during the spring to prevent fruit infection. Apply chlorothalonil (Daconil) or Captan (except on apricot) from pink bud through shuck-split stages, depending on the frequency of rainfall.

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