Causal Agent: Xanthomonas vesicatoria.
(Synonym: X. campestris pv. vesicatoria).
At least three races have been reported.
Distribution:
Worldwide
Symptoms:
Symptoms can appear on all above ground parts of the plant. The first
symptoms observed on the leaves are dark, water-soaked, circular spots
that are less than 3 mm in diameter. These spots become angular and the
surface may appear greasy with a translucent center and a black margin.
The centers of these lesions soon dry and crack, and a yellow halo. may
surround the lesion. Lesions tend to be more numerous on the young
foliage. During periods of high moisture (heavy rain, fog or dew) leaves
will take on a blighted appearance rather than the typical leaf spots.
Fruit infection begins as small, black, raised specks which may be
surrounded by a white halo that has a greasy appearance. These lesions
can enlarge to 4-5 mm (0.25 inch) in diameter and become brown, slightly
raised and scabby in appearance. They can also have raised margins and
be sunken in the center.
Conditions for Disease Development:
The bacterium can survive in crop debris, on volunteer plants, weeds and
seed. This disease spreads rapidly through seed beds and fields by
sprinkler irrigation and wind driven rains. Infection generally occurs
through wounds, such as those made by insects, wind driven sand and
rain, and by high pressure spraying. Warm (24-30°C, 75-86°F)
temperatures with sprinkler irrigation or heavy rains, favor disease
development.
Control:
The use of disease free seed and transplants is important for the early
control of bacterial spot. Copper sprays can provide moderate levels of
protection. When bacterial spot is
present, avoid the use of
Foliar
symptoms in the field.
Leaf lesion with chlorosis.
Leaf
lesions with black margins. Small lesions on green fruit.
Small
and large lesions on red fruit.
overhead irrigation. Rotation to non-host crops
and controlling weeds and volunteer plants are good preventative measures.
Good sanitation practices, which include cleaning equipment used in
diseased fields and plowing under all plant debris immediately after
harvest, can reduce losses from this disease.