(1) Bacterial blight, also known as "iron leaf" or "blight leaf blight," is caused by a deuteromycete fungus called *Septoria scrophulariae*. This disease is more prevalent during the rainy season and is commonly found in both northern and southern regions. Early symptoms include small purple-brown spots on the leaves, which gradually become sunken as the lesions expand into irregular, round, or polygonal shapes. The larger lesions appear gray-brown and are often separated by leaf veins, with a wide purplish-brown border around them. Black specks can be seen on the affected areas. In severe cases, the infected leaves may die off. To manage this disease, it is important to clear the field after harvest and remove all diseased plants. Good field management, including proper drainage and ventilation, is essential. Spraying a 1:1:100 Bordeaux mixture or 65% zinc oxide at a 500-fold dilution before and at the onset of the disease, repeated every 7–10 days, can help control its spread.
(2) The pathogen responsible for blight is a fungus known as *Sclerotium rolfsii*, which affects the roots and rhizomes of plants. This disease is common in southern regions and tends to occur from June to September, especially after heavy rains in Jiangsu. Infected roots become rotten, covered with white, thread-like hyphae, and yellow to brown sclerotia of rapeseed. The mycelium and small sclerotia can spread to the main stem, causing rapid wilting and death of the plant. Control measures include rotating crops with cereals to avoid continuous planting. Field management should focus on good drainage and air circulation. In rainy areas, planting oyster mushrooms can help reduce disease pressure. Diseased plants should be removed promptly, along with contaminated soil, and lime should be applied to disinfect the area. Before planting, seeds can be treated with a 50% thiram solution diluted 1000 times for 5 minutes and then dried before sowing.
(3) Red spider infestations cause visible damage to leaves, resulting in white spots, yellowing, and eventual drying of the foliage. In addition to red spiders, other pests such as tigers and locusts can also harm crops. For tigers, manual collection or the use of bait is effective. Locusts can be controlled using insecticides like dimethoate or tobacco ash water. Regular monitoring and timely intervention are key to preventing significant crop losses.
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