Back to top

Bacterial Leaf Spot

Bacterial Leaf and Fruit Spot

The foliage and fruit of many plum, peach and apricot varieties is susceptible to infection by bacterial leaf spot, Xanthomonas arboricola, that causes small yellow spots and a shot-hole appearance in foliage.  Fruit infection leads to round, sunken spots that detract from the appearance and marketability of fruit.  These symptoms can be confused with spray injury.  Warm weather and moisture favor its spread, as do nearby susceptible peach and apricot trees.  Other names for this disease are bacterial shot-hole and bacteriosis.

Plum and peach varieties vary in susceptibility. Shiro and Early Golden have a high degree of susceptibility. Obilinya and Vanier have some resistance. In general, European plums are more tolerant than Japanese varieties. The most effective management strategy is to plant resistant varieties of plum and peach since chemical sprays are of limited use in preventing this disease.  Removal of branches and limbs with cankers during dormant pruning can reduce disease pressure. 

In early summer, signs of bacterial leaf spot first appear as watersoaked spots on the leaves. The shape of the spots is more angular than round. They eventually turn yellow and fall out which creates the shot-hole appearance. The shot-hole effect is more pronounced on plum than peach, whereas in peach, the lesions turn brown with extended areas of yellowing.  Fruit infections lead to sunken spots that easily crack with fruit expansion.

Copper sprays are more effective for prevention than control, and are of limited use due to phytotoxicity.  Consequently, planting resistant varieties is the most effective management strategy.