Bacterial Leaf Spot

Xanthomonas arboricola

The most obvious leaf symptoms are yellow, chlorotic leaves with angular lesions at the leaf tip, mid-rib, and/or along the leaf margin. Infected leaves frequently experience premature drop. Developing foliar lesions are water-soaked, sometimes grayish colored, and angular in shape, being delimited by the veinlets of the leaf. Initially, individual lesions are only 1 to 2 mm in size, usually expanding to 2 to 3 mm, but seldom exceeding 5 mm. As lesions age, centers may become dark or purple in color and necrotic; when lesion center abscission occurs, a shot-hole appearance results. The very earliest leaves to emerge in spring, on some varieties before bloom, can become infected and serve as secondary sources of inoculum for later emerging leaves and fruit. Leaves are most susceptible before becoming fully expanded. Leaf symptoms usually are first visible 5 to 14 days after infection. Rapid symptom expression is dependent on warm temperatures.

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