Black rot in cole crops is a major challenge, particularly during seasons with above-average rainfall, when the pathogen is more likely to cause serious problems. Black rot is caused by the bacterium Xanthomonas and is a difficult disease to control once it has established itself in your fields. For this reason, preventative management is essential.

The pathogen gains entry into the plant through hydathodes, which are openings located along the leaf margins. At night, when transpiration ceases, the plant exudes xylem sap through these openings in a process known as guttation. When transpiration resumes in the morning, the plant reabsorbs these droplets. If Xanthomonas is present, the bacteria can enter the plant together with the droplets. This is why black rot can often be identified in the field by its characteristic V-shaped lesions that develop from the leaf edge.

If your crop has strong cell walls, it becomes much more difficult for the pathogen to cause severe damage. Nutrients such as potassium, calcium and boron play an important role in strengthening cell walls. High-quality formulation products can effectively correct deficiencies in these elements. Including regular silicon foliar sprays in your spray programme is also an excellent preventative measure. Registered copper products and disinfectants can also provide effective control of the pathogen.

In South Africa, certain cultivars have a higher level of genetic tolerance to black rot, including Optima and Powerslam from Sakata. Be sure to plant these cultivars during seasons when black rot is known to be prevalent and poses a significant risk.

For more information, contact your nearest Novon representative or visit Novon’s website at www.novon.co.za