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Occurrence and Prevention of Pansy Disease
Leeks are perennial vegetables that require a long growing period. As the continuous cropping period increases, the concentration of pathogenic bacteria rises, leading to more severe disease outbreaks. In some fields, the disease incidence can reach as high as 70%. Therefore, it is crucial to implement effective prevention and control measures. The following details the symptoms, causes, and management strategies for leek diseases.
I. Symptoms of the Disease
Initially, the affected leaves show dark green water-soaked lesions. These areas gradually contract, causing the leaves to turn yellow and wither. During wet weather, the lesions become soft and rotten, with a gray mold appearing on the surface. The leaf sheaths develop brownish, water-soaked lesions, which also soften and rot, leading to leaf stripping. The bulbs and roots are also affected, showing soft rot, which hinders the plant's ability to absorb and store nutrients, ultimately affecting its growth and yield.
II. Conditions Favoring Disease Occurrence
Diseases tend to occur more frequently during summer when temperatures are high and humidity is elevated. Fields that are low-lying, have poor drainage, or experience weak plant growth due to over-harvesting, nutrient deficiency, or improper care are particularly vulnerable. These conditions create an ideal environment for pathogens to thrive and spread rapidly.
III. Control Methods
1. Crop Rotation: It is recommended to rotate leek planting with non-onion and non-garlic crops for at least three years. This helps break the disease cycle and reduces pathogen buildup in the soil.
2. Land Preparation and Drainage: Level the field and ensure proper drainage systems are in place. After heavy rains, avoid waterlogging and eliminate any puddles that may form. Good drainage prevents excess moisture, which is a key factor in disease development.
3. Cultivating Healthy Plants: Select strong seedlings and remove any diseased ones early. Pay attention to root development and avoid over-harvesting. Apply additional fertilizer after harvest and ensure proper irrigation during the summer. These practices promote vigorous plant growth and improve resistance to diseases.
4. Leaf Management: Before the rainy season begins, remove the lower yellow leaves and pick up the green leaves. Secure them with loose grass or straw to keep them off the ground, improving air circulation around the plants and reducing the risk of infection.
5. Chemical Control: From mid-July to early August, apply fungicides such as 25% metalaxyl WP diluted at 600–800 times, 64% mancozeb WP at 500 times, or 0.1%–0.2% copper sulfate. These solutions should be deeply irrigated into the root zone or applied directly to the rhizomes for optimal effectiveness.
By implementing these integrated management strategies, farmers can significantly reduce the occurrence of leek diseases and maintain healthy, productive crops throughout the growing season.