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Young, green apricots or peaches develop small, crusty spots that persist as the fruits mature. Fruits on the same tree may have only a few spots or they may be covered more densely.

Courtesy Meredith Seaver, USU Extension

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The fruit stage in the spring, where the dry remains of the blossom split or drop away from the fruitlet, is called shuck split. This stage helps orchardists know it's time to do a protective spray on their stone fruit trees.

Courtesy Meredith Seaver, USU Extension

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When softer ripe or nearly ripe apricots or peaches are infected with Coryneum blight, the spots are sunken and larger than the spots that develop early in the season.

Courtesy Meredith Seaver, USU Extension

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The necrotic spots that dry and drop out of infected leaves give Coryneum blight its common name of shot hole disease.

Courtesy Meredith Seaver, USU Extension

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Did your apricots or peaches have crusty spots or “freckles” on their skins this summer? If so, you may have been seeing the effects of Coryneum blight, a fungal disease. It may seem like our growing season is winding down and there’s not much left to do in your home orchard, but now is one of the most important times for controlling this disease.

Coryneum blight is a fungal disease that affects stone fruit trees and their ornamental relatives. It is most common on peaches and apricots. Fungal spores overwinter on the leaf scars left behind when leaves drop from the tree. Buds beside the infected scar tissues die, and small twigs can be girdled and killed when that happens. These bud infections become the source for new leaf and fruit infections in the spring. Coryneum blight also causes necrotic spots on the leaves that dry and drop out, leaving small holes that give this disease it’s common name of shot hole disease.

Early season infection on younger fruits can look like crusty freckles or bumps. Recent infections on ripe or nearly ripe fruits can cause soft, sunken, necrotic spots, but a late-season infection may not always show up on leaves. Infected fruit is still safe to eat, and the spots can be peeled off or trimmed away if the damage is minor.

So, what should you do for your affected trees this fall? Check your trees frequently, watching for the leaves to begin dropping. Sometime in the next few weeks, you’ll see that about 50% of the leaves have dropped from the tree. Once that happens, spray your stone fruit trees with chlorothalonil or copper. Thorough coverage is needed to provide protection for all the leaf scars on the tree.

There are a few more things you’ll need to do to reduce or prevent this problem in future years.

• Wet or humid conditions make it easy for Coryneum blight to spread. Prevent sprinklers from hitting the canopy of the tree.
• In the fall, spray the tree with a fungicide when 50% of the leaves have dropped from the tree. Look for one with the active ingredient chlorothalonil, myclobutanil or copper. A hose-end sprayer works well for job as the stronger water pressure knocks off more leaves, protecting more leaf scars.
• Prune out and dispose of dead twigs, twigs with dead buds and twigs with dark, sunken bark.
• Clean up thoroughly under the tree once all the leaves have dropped.
• In the spring, spray the tree again with chlorothalonil, myclobutanil or copper a few days after the petals drop from the blossoms but before “shuck split.” You can see an example of shuck split in today’s photos.
• During the summer, use protective sprays of copper or myclobutanil when rain is in the forecast. Chlorothalonil can’t be used after shuck split until the fruit has been harvested.

If Coryneum blight has affected your stone fruit trees for multiple seasons, it may take a few years of careful management to eliminate the problem.