Plant Protection Knowledge
Symptoms and control of Bacterial Spot
Bacterial leafspot is a severe disease of peppers and tomatoes in Barbados. It is more prevalent during wet seasons. Damage to the plants includes leaf and fruit spots which result in reduced yields, defoliation, and sun scalded fruit.
Causative agent: Xanthomonas campestris pv vesicatoria
Symptoms
The disease can affect all the aboveground parts of the plant; leaves, stem and fruit.
Leaves and stems
Small circular brown spots are seen on the leaves and stem. Frequently these spots will coalesce (join together) to give long brown streaks. Affected leaves will eventually turn entirely brown and die but will not drop from plant. This is what is known as blight.
Fruit
On the fruit the disease presents itself as small, brown, pin like raised spots, which increase in size and give a scab-like appearance. In the early stages a yellow halo (zone) can be seen around these spots on the fruit. This disappears as the disease progresses.
Crops affected
Tomatoes, Sweet pepper.
Damage
In the early stages reduction in yield will occur due to destruction of the leaf surface. If the infection is severe or left unchecked the plants will eventually die because of the damage done to the leaves.
Although a reduction in the size of the fruit also occurs, it is the scabby appearance however of the fruit and hence it’s reduced marketability that have the greatest impact on the farmer’s profits.
Conditions which favour the disease
High humidity, rainfall and temperatures between 24-30oC favor the development of the disease. Therefore the disease is most prevalent during the rainy season or where overhead irrigation is used.
Rain/water droplets help spread the infection and any damage done to the plant by insect or mechanical makes the situation worse.
Control
- Crop rotation – avoid planting tomatoes and sweet peppers together or one following the other in the same bed
- Plant clean seed material since it is known that the disease can be transmitted this way
- Remove all volunteer plants from area and burn rogues before any new plantings
- Select healthy seedlings. If the farmer is producing his own seedlings, this is should be done in an area where the incidence of the disease is low or where there are no peppers or tomatoes planted.
During the rainy season especially after a heavy shower, preventative fungicidal spraying should be done at the earliest possible time.
Copper based compounds such, as Kocide, Champ and Champion should be used. These should however be alternated with zinc or manganese based compounds such as Zineb/Ziram and Maneb.
This helps to reduce the incidence of resistance when over reliance on one chemical occurs. This should also be followed where overhead sprinklers are used.
It should be noted that spraying the fungicide would not cure the problem. It controls the infection level if the disease is present and reduces the incidence by making the plant environment inhospitable to the organism.