Xanthomonas campestris pv. campestris

Black Rot is one of the most destructive bacterial diseases of brassicas in South Africa. It shows up as yellowing leaf edges that develop into distinctive V-shaped lesions pointing toward the midrib. Eventually, the veins blacken and the entire plant may wilt and rot. The disease thrives in warm, humid weather and spreads rapidly through infected seed, water splash, tools, and even hands. Once established, it’s difficult to contain, especially in crowded beds with poor air movement.

Because Black Rot is bacterial, not fungal, traditional fungicides have no effect. This makes prevention critical. Once symptoms appear, it’s often too late to save the crop. Losses can be severe, with infected transplants spreading the disease to an entire bed. For organic growers, effective control relies on clean seed, strict sanitation, and strategic water management rather than reactive spraying.

Start with hot-water-treated seed or source from reputable suppliers who guarantee disease-free stock. Use a 3- to 4-year rotation away from brassicas to reduce bacterial survival in the soil. Avoid overhead watering. Instead, opt for low-splash techniques such as the Livingseeds Drip Irrigation System which keeps foliage dry and dramatically reduces the spread of bacterial pathogens. Promptly remove infected plants and control cruciferous weeds that can host the disease between crops.

• Organics

  • Copper Soap
    A fatty acid and soluble copper formulation that may help suppress early bacterial spread when used as a preventative spray. Apply at first sign of symptoms and repeat every 7 to 10 days.

Note: Black Rot is almost always introduced through seed or crop residue. For seed saved at home, consider a hot-water treatment at 50 °C for 25–30 minutes followed by a thorough rinse and dry. Combine sanitation and copper-based preventative spraying for best results.