(1) Bacterial blight, also known as "iron leaf" or "blight leaf blight," is caused by a deuteromycete fungus called *Septoria scrophulariae* West. This disease tends to be more severe during the rainy season and is commonly found in both northern and southern regions. At the early stage of infection, small purple-brown spots appear on the leaves. These lesions gradually become sunken and expand into polygonal, round, or irregular shapes. Larger lesions turn gray-brown and are often separated by leaf veins. A wide purplish-brown border surrounds the affected areas, and numerous small black spots can be seen within the lesions. In severe cases, the infected leaves eventually die. To manage this disease, it is recommended to clear the garden after harvest and remove all diseased plants. Proper field management, including good drainage and ventilation, should be maintained. As a preventive measure, spraying a 1:1:100 Bordeaux mixture or a 65% zinc oxide solution diluted 500 times is effective. Apply the treatment before the disease appears and repeat every 7 to 10 days for several consecutive applications.
(2) The pathogen responsible for blight is a fungus known as *Sclerotium rolfsii* Sacc. It primarily affects the roots and rhizomes of plants. This disease is more common in southern regions and is particularly severe in Jiangsu from June to September, especially after heavy rains. Infected roots become rotten, and the root area and surrounding soil are covered with white, silky mycelium. Yellow to brown sclerotia of rapeseed may also appear. The mycelium and small sclerotia can spread to the main stem, causing rapid wilting and plant death. Control measures include rotating crops with cereals to avoid continuous planting of the same crop. Field management should focus on proper drainage and air circulation, especially in rainy areas where raised beds are recommended. Diseased plants and contaminated soil should be removed promptly, and lime can be applied to disinfect the area. Before planting, seeds can be treated with a 50% thiram solution diluted 1000 times for five minutes, then dried before sowing.
(3) Red spider infestations cause damage to leaves, resulting in white spots, yellowing, and eventual drying of the foliage. Other pests, such as grasshoppers and locusts, also pose threats to crops. For grasshoppers, manual collection or the use of bait can be effective. For locusts, insecticides like dimethoate or tobacco ash water can help control the damage.
In summary, proper identification of the pest or disease is crucial for effective management. Regular monitoring, timely intervention, and good agricultural practices are essential to reduce losses and maintain healthy crop growth.
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