Mustard black spot disease is commonly observed during the rainy season and can significantly affect both the quality and yield of the crop. Timely application of **pesticides** is essential to prevent severe damage. The pathogen responsible for this disease is *Alternaria brassicae*. Symptoms typically begin on the outer leaves, where round, brown or dark brown lesions appear, ranging from 4 to 6 mm in size. These lesions often display distinct concentric patterns and may be surrounded by a yellow halo. On stems and petioles, the lesions are elongated, dark brown, and slightly sunken. On the peduncle and seed pods, the lesions vary in shape and color, and black mold may develop when the area is moist. In severe cases, the leaf lesions merge, leading to leaf death or complete desiccation.
The pathogen overwinters in the form of mycelium or conidia on infected plant debris, seeds, or in storage. It can also survive on host plants during winter. The disease spreads through wind and rain. The pathogen thrives between 10°C and 35°C, with an optimal temperature around 17°C. High humidity, above 80%, is critical for disease development. If relative humidity drops below 75%, the disease tends to be mild or absent. According to the **pesticide network**, the early growth stage of autumn-sown cabbage occurs from late August to early September, with rapid growth from September 19 to October 7. After October 10, the crop generally develops smoothly. The epidemic is not related to the total rainfall but rather the number of rainy days. If there are more than four days of rain, especially if it’s continuous, the disease can become widespread. Therefore, high humidity, heavy rain, and low temperatures are key factors in disease occurrence.
The severity of the disease is also influenced by cultivation practices. Early planting, high density, low-lying fields, poor management, lack of water, insufficient fertilization, and weak plant growth can all contribute to increased disease incidence. To manage mustard black spot disease effectively, several control methods are recommended:
1. **Use resistant varieties**: Cultivars such as Xiaoqingkou, Qingqing, Beijing No. 1, Beijing No. 5, Beijing 88, Zhengza No. 2, Luoyang Tokyo No. 3, Zhengbai No. 4, Jinqing No. 9, Jin No. 3, Shuangqing 156, and Shuangqing are known for their resistance to the disease.
2. **Seed disinfection**: Use seeds from healthy plants, or soak them in warm water at 50°C for 25 minutes before transferring to cold water. Dry the seeds thoroughly before sowing. Alternatively, treat seeds with 0.3% chlorhexidine wettable powder (by weight) or 0.4% acesulfame powder.
3. **Improve field management**: Practice crop rotation, avoiding cruciferous vegetables for at least two years. Plant cabbages away from other cruciferous crops. Apply well-decomposed organic fertilizer and increase phosphorus and potassium application. Proper fertilization helps improve plant health and disease resistance. Remove and destroy diseased leaves and plant parts promptly, either by burying or burning them.
4. **Apply fungicides**: In the early stages, use 50% phorhin WP diluted 1000 times, 50% carbendazim WP diluted 800 times, 50% thiram double WP diluted 500 times, 40% sterilized Dan WP diluted 400 times, 64% anti-virus WP diluted 500 times, or 50% keeling WP diluted 1000 times. According to the **China Pesticide Network**, 70% mancozeb WP diluted 400 times is also effective. Spray the solution every 7 days, repeating 3–4 times as needed.
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