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There are four identified species that cause Bacterial Spot in peppers, tomatoes and other solanaceous plants. Xanthomonas campestris pv. Vesicatoria is the most common species found in Australia.
Here’s what to keep in mind when managing Bacterial Spot:
The first visible symptom of Bacterial Spot is small water soaked areas on the underside of the leaf. These quickly enlarge becoming dark brown and slightly raised.
On the upper side of the leaf, these spots are slightly depressed with a dark brown border and a beige centre.
Infected leaves turn yellow and drop prematurely. This defoliation exposes young fruit to sunscald and reduces the plants ability to adequately support fruit development. It causes a shedding of blossoms and abortion of developing fruit. Although Bacterial Spot does not directly rot the fruit, it causes lesions which enable other rotting pathogens to enter.
Bacterial Spot thrives in periods of warm temperatures and prolonged wet conditions.
The X10R® pepper varieties from Seminis include a compliment of Bacterial Spot resistance genes that provide at the least intermediate levels of resistance to all currently known races of the bacterial spot pathogens.
Even when planting resistant pepper varieties, it is imperative to use an integrated approach to management. This should include eliminating potential sources of inoculum, protecting plants from infection, reducing favorable disease conditions and regularly monitoring for symptoms.
Infected seed and transplants can be the initial source of inoculum. The pathogen can survive on the surface of seedlings, causing no visible symptoms until transplanted to the field.
To protect seedlings during transplant production, all materials, surfaces and benches should be regularly cleaned and disinfected. Humidity levels should be kept as low as possible and all seedlings should be examined for symptoms.
In-field practices, such as the control of solanaceous weeds and volunteer plant removal can reduce levels of inoculum. As the pathogen can survive on infested crop debris for up to one year, it is critical to quickly disk or plow the field after the final harvest. It is also important to manage weeds and volunteer host plants which have the potential to be sources of inoculum.
Avoiding the use of overhead sprinkler irrigation and working in the fields when plants are wet, may slow the spread of the disease. The disease can easily be spread on on worker’s clothes, tools and field equipment when free moisture is present.
Rotation and separation
A minimum of one year rotation away from peppers and other solanaceous crops is highly recommended, with a three-year rotation preferred. During the season all pepper, tomato, eggplant and potato varieties should be planted as far away from each other as possible.
Application of fixed copper bactericides such as Champ® or Kocide® can be used to slow the spread of the disease. When combined with other products such as Tanos® or Serenade® it can eliminate copper resistant strains, enhancing activity and improving control.