In the lower reaches of the Yangtze River, the climate is characterized by moderate temperatures and humidity, along with ample sunlight. These conditions create an ideal environment for the proliferation of certain pathogens, often leading to serious damage in ornamental plants. To help gardeners and horticulturists manage these issues effectively, this article outlines the symptoms and control methods of three common plant diseases.
**First, Powdery Mildew**
1. **Symptoms**: This fungal disease primarily affects leaves but can also infect stems, petioles, buds, and flowers. Initially, small white powdery spots appear on infected areas and gradually expand. Under favorable conditions, the entire leaf can be covered within 7–10 days, giving a frost-like appearance. Infected leaves may become distorted, wilted, or even die, severely impacting plant growth and flowering. Flowers such as chrysanthemums, impatiens, euonymus, cineraria, dahlias, roses, and many others are particularly susceptible.
2. **Control Methods**: Proper cultivation is key. Ensure good air circulation and avoid excessive nitrogen fertilization. Water appropriately and remove diseased parts promptly. At the early stage, a 1:1:140 Bordeaux mixture can be used. Once the disease appears, apply 25% triadimefon at 1000 times dilution or 70% thiophanate-methyl at 1000 times. Repeat every 10 days for 2–3 applications to achieve effective control.
**Second, Leaf Spot (Brown Spot)**
1. **Symptoms**: This disease mainly affects the leaves, starting with brown spots that grow larger over time. The lesions often have a reddish-brown border and a gray-white center, with black spores appearing later. In severe cases, the entire leaf may be affected, leading to premature leaf drop and plant decline. Plants like rhododendrons, jasmine, camellias, lotus, and water lilies are especially vulnerable.
2. **Control Methods**: Remove and destroy infected leaves immediately. Before symptoms appear, spray a 1:1:200 Bordeaux mixture every 7–10 days. Once the disease is detected, use 65% zoxamide WP diluted 500 times or 70% thiophanate-methyl at 1000 times. Alternatively, 50% carbendazim can be applied as a soil drench.
**Third, Anthracnose**
1. **Symptoms**: This disease affects leaves, stems, and petioles. Early signs include small, water-soaked spots that develop into gray-brown lesions with a red margin. Lesions may eventually turn white and become translucent, causing holes in the leaves. When petioles or stems are infected, they may turn brown and die, leading to overall plant decline. Plants such as camellias, roses, orchids, lilies, and cacti are commonly affected.
2. **Control Methods**: Improve air circulation and avoid overwatering. Apply phosphorus and potassium fertilizers, and remove infected plant parts immediately. At the onset, spray 50% mancozeb at 500 times dilution or 70% thiophanate-methyl at 1000 times. For best results, alternate between different fungicides and repeat the treatment every 10–15 days for 2–3 times.
By understanding these diseases and implementing timely control measures, gardeners can significantly reduce the impact of these pathogens and maintain healthy, vibrant plants.
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