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Bacterial Leafspot of Stone Fruits

This disease is caused by a bacterium (Xanthomonas) that thrives in the rainy June and July weather we have experienced throughout most of the state (apologies to those of you who still have dry weather). Look for the disease on peach, nectarine, almond, apricot, plum, prune, and cherry, as well their ornamental equivalents.

Numerous spots (from as small as a pinprick up to 1/5 inch in diameter) form in the leaves. At first these spots are circular and watersoaked, but soon enlarge to become angular and deep purple to rusty brown or black. The centers of the spots often dry out and tear away, so you may notice only a shot-hole appearance or even a wind-tattered effect.

Infected leaves turn yellow and drop early. Although symptoms resemble those of nitrogen deficiency, that deficiency usually results in holes concentrated near the midvein on the leaf. This bacterium also attacks twigs and fruit, reducing fruit quality and yield or reducing aesthetic appeal in the case ornamental species.

Some peach cultivars have resistance to bacterial leafspot. Most apricot varieties are susceptible, as are many nectarine varieties. Some resistant cultivars of peach are listed in Report on Plant DiseasesNo. 810, Bacterial Spot of Stone Fruits.

If you have a mature tree and do not wish to consider replacement with a resistant variety, use balanced fertility practices and open the trees through pruning so that air circulation is improved. These steps will make conditions less conducive to disease development.

Author: Nancy Pataky


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