Bacterial spot is the most destructive leaf disease of capsicum. Black rot of brassica plants often follows infection by bacterial spot.
The bacterium Xanthomonas campestris.
The first symptoms are usually small, yellow V-shaped areas developing along the leaf margin. These areas soon turn brown and dry out. Vein blackening may extend down the leaves into the petiole and the stem. When the stem is cut across, a black ring will be seen in the water-conducting tissues just below the bark.
Soft, rotting organisms often quickly follow the invasion of fleshy leaves and petioles. Black rot bacterium then cause the plants to rot rapidly.
Tan, circular spots with yellow halos can also develop between the veins. These coalesce and dry out to give the tattered leaf scald appearance.
Infection of young, immature curcubit fruit causes small water-soaked areas of pronounced, light brown ooze. As the fruit enlarge, the ooze dries to form a raised, yellow crust over the spot. The flesh beneath the spots is often water-soaked, extending to the seed cavity and resulting in seed contamination.
|How does it spread?|
The bacterium may be introduced in seed or in surviving undecomposed crop residue or other host plants. Bacteria spread in water splash during wet, windy weather or by overhead irrigation. It can also disperse on insects, or on people or equipment moving through the crop.
Warm, humid weather favours rapid disease development.
A serious disease of many crops such as capsicum, tomato, potato, eggplant, Asian vegetables, cabbage, brussel sprout, pumpkin, melon, lettuce, bean, carrot and stone fruit. It is a minor disease of sweet corn. The disease can survive between crops on nearby host crops and on many weeds.
Worldwide, there are 11 known races of bacterial spot that affect capsicum. Not all of these have been found in Queensland. No variety has resistance to all races of bacterial spot, but to be effective, the variety used must have resistance to all the races present.
Use as many of the following practices as possible in an integrated program to manage bacterial spot.
Chemical registrations and permits