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Figure 1. Bacterial spot on leaves.

Figure 2.Bacterial spot on fruit.

Bacterial spot -- caused by the bacterium Xanthomonas compestris pv pruni -- is a common peach disease in Kansas. It may cause significant damage to trees in certain locations. The disease affects leaves, fruit, and occasionally twigs of peach. Leaf infections first appear as small, pale green to yellow angular spots. These spots normally are more prevalent near the leaf tip and are surrounded by a yellow halo. Eventually, the lesions turn dark brown, separate from healthy tissue, and drop out, giving the leaf a shot-hole appearance. On susceptible cultivars, 1 or 2 leaf lesions can cause a complete yellowing of the leaf and result in premature defoliation.

One of the most serious aspects of the disease is the development of spots on the fruit. The spots are mostly superficial, but numerous infections can cause pitting and cracking of the fruit surface. The fruit cracks may show gumming.

DISEASE CYCLE

The bacterium overwinters in small, blister-like cankers on the twigs. In early spring, the cankers rupture and release millions of bacteria. These bacteria are dispersed by splashing water and infect developing leaves and fruit. Infection is favored by frequent rainfall accompanied by high winds and moderate temperatures in June and July. Extended periods of hot, dry weather inhibit disease development.

CONTROL 

Peach cultivars vary in their susceptibility to bacterial spot, although no variety is immune. Those cultivars showing tolerance to the disease include Redskin, Redhaven,

Web updated 9/01/06
Web comments to jpierz@ksu.edu