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Bacterial Fruit Blotch
Causal Agent: (bacterium - Acidovorax avenae subsp. citrulli)
Infected
seedlings initially develop water-soaking on the lower surface of cotyledons
and leaves [Picture]. These areas then become necrotic
[Picture]. The pathogen can also cause non-distinctive,
necrotic leafspots on transplants [Picture]. On leaves
of more mature plants, the pathogen can cause large, circular brown lesions,
usually near the edge of the leaf, but this is not reliable for diagnosis. The
unique symptoms are: irregular, rust-colored lesions that run along leaf ribs
[Picture], while on the underside of the leaf, the leaf
rib is water-soaked [Picture]. Leaf lesions can serve
as a source of bacteria that can infect fruit. In the field, leaf lesions are
often difficult to find and may be confused with lesions caused by pathogenic
fungi.
Where this disease has occurred, watermelons and other cucurbit crops should not be replanted in the field for at least one season, crop debris should be plowed under, and volunteer plants destroyed. Cucurbit weeds such as citron melon should also be controlled. Copper-based fungicides should be applied on a regular schedule at the time of flowering or earlier, if transplants are used.
Fruit
symptoms start as water-soaked spots that rapidly enlarge. Symptoms are generally
seen in the light portions of striped fruit [Picture].
The lesions later turn brown and crack [Picture]. The
pathogen is introduced to a field by planting contaminated seed or transplants.
Within the field, the bacteria spread to healthy plants via rain or overhead
irrigation, especially under conditions of high humidity and temperature. The
fruit are most susceptible to infection around the time of pollination. As the
fruit matures, it becomes resistant to infection. Once introduced into a field,
the bacteria can persist on volunteer watermelon or citron [Picture]
plants, or in their seed. Cantaloupe and honeydew melons are also susceptible
to this pathogen.
Where this disease has occurred, watermelons and other cucurbit crops should not be replanted in the field for at least one season, crop debris should be plowed under, and volunteer plants destroyed. Cucurbit weeds such as citron melon should also be controlled. Copper-based fungicides should be applied on a regular schedule at the time of flowering or earlier, if transplants are used.
For more information, see the following publication: L-5222
Bacterial Fruit Blotch of Watermelon
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