Bacterial spot

Xanthomonas pruni

Bacterial spot attacks the fruit, leaves, and current season's twigs. Fruit infections appear as tiny purple to black flecks on the fruit surface of peaches, and as water-soaked spots on nectarines and other smooth skinned Prunus spp. Later, the skin is "broken" and the flesh beneath the spot becomes sunken. Early season infections result in very deep lesions in the flesh, and infections within 30 days of harvest result in circular, yellowish spots on the fruit surface (photo 2-62). The leaf spots are always angular as a result of being restricted by the veins of the leaf (photo 2-63). Initially, the spots appear as water-soaked angular spots which are generally only visible when viewed with a light source behind the leaf In about three days, the lesion becomes visible with reflected light. Within one to two weeks, the center of the lesion is "walled off" by the leaf and drops out, resulting in a shothole or tattered appearance. Leaf lesions are much more common at the distal ends of the leaves and around major leaf veins. This occurs because the water film is thicker in such areas and these regions of the leaf dry more slowly. Leaves with as few as two to three lesions turn yellow and fall. Under heavy disease pressure, only the youngest leaves remain on the tree.

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