Occurrence and Control of Black Cauliflower in Green Cauliflower
August 21 20:01:29, 2025
Black rot is a serious bacterial disease that affects plants from the seedling stage through to maturity. In young seedlings, the cotyledons become water-soaked and quickly wilt and die. As the plant matures, the disease primarily targets the leaves, starting at the edges and progressing inward in a characteristic "V"-shaped lesion. These lesions are typically yellow-brown with a pale yellow margin. The infection can also affect the roots, causing the vascular bundles to turn black and leading to internal dry rot. In severe cases, the entire plant may wilt and die.
The disease is caused by bacteria of the genus *Xanthomonas*. These pathogens overwinter on seeds, infected plant debris, or in the soil. They can be spread by insects, farm equipment, and human activities. Infected seeds are the primary source of infection, as they can carry the bacteria long distances. When contaminated seeds are sown, the pathogen enters through the water stomata at the edge of the cotyledons, spreading into the vascular system and eventually infecting the whole plant. Bacteria in the soil can be transported to the leaves via rain or irrigation water. They enter through leaf stomata or natural openings, first infecting a few mesophyll cells before moving systemically into the vascular tissue.
Environmental conditions play a major role in disease development. High temperatures (between 5°C and 39°C) and high humidity (over 95%) favor the spread of the disease. The optimal temperature range is 25°C to 30°C. Leaf dew and water splashing on the leaf edges also promote bacterial entry. Other contributing factors include early sowing, low-lying fields, clayey soils, excessive watering, continuous cropping of cruciferous crops, improper fertilizer use, and heavy pest infestations.
To manage black rot, several preventive and control measures are recommended. First, select disease-free seeds and treat them before planting. Soak seeds in warm water at 50°C for 20 minutes or in a 1000-fold dilution of streptomycin for 2 hours. For direct seeding, apply 40% of the seed weight in a fungicide treatment like 50% FMC. Field management is also crucial—rotate crops in severely affected areas, avoid overwatering, ensure proper drainage after rain, and remove diseased leaves promptly. At harvest, all infected plant material should be removed to reduce the initial inoculum.
Chemical control options include applying 200 ppm streptomycin, 100 ppm neomycin, 60% chlorothalonil wettable powder diluted 600 times, or a Bordeaux mixture (1:1:200 to 1:1:240). Another option is 77% copper oxychloride WP diluted 500 times. Alternating these treatments can help prevent resistance and improve disease control effectiveness.
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