Bacterial Spot of Peach
Agricultural Extension Service
The University of Tennessee
Bacterial spot, known also as bacteriosis, bacte-
rial shothole, or shothole, is caused by the bacterium
Xanthomonas campestris pv. pruni. Although primarily
a peach and nectarine problem, this disease also occurs
on apricots, plums and, to a lesser degree, cherries.
Losses due to bacterial spot occur from affected
fruit and from the devitalization of trees caused by
frequent defoliation. Such weakened trees are more
subject to winter injury. Losses are greatest in light,
low-fertility soils. Trees low in vigor are more suscep-
tible to bacterial spot than vigorous trees.
Numerous small spots form on the leaves. The
spots are angular, purple to purplish-brown or black.
Spots may merge and the centers may fall out, giving
the characteristic “shothole” appearance. Heavily
infected leaves turn yellow and drop. Severe leaf loss
early in the summer reduces fruit size and weakens the
tree. A few lesions can result in severe defoliation on
sensitive varieties; tolerant varieties may require many
more lesions for defoliation.
On fruits, tiny water-soaked, sunken spots form.
The spots enlarge and merge to cover large, irregular
areas. As the fruit grows, cracking or pitting occurs in
the lesions. The brown rot fungus can easily enter these
cracks and become established. Every effort to control
brown rot should be made when deep bacterial spots
form on fruits.
The bacterial spot organism infects only cur-
rent-season growth. On twigs, two types of cankers
form. “Summer cankers” develop on green twigs,
usually after leaf spots are evident. The lesions begin
as water-soaked, purplish spots between the nodes.
The cankers enlarge, become slightly sunken and are
circular to elliptical in shape. Cankers caused by the
peach scab fungus are similar, but scab cankers are
Steve Bost, Professor
Entomology and Plant Pathology
Infections that occur late in the year on young,
succulent twigs s