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Occurrence and Prevention of Pansy Disease
Leeks are a perennial vegetable that require a long growing period. As the continuous cropping cycle increases, the concentration of pathogenic bacteria becomes more pronounced, leading to more severe outbreaks of disease. In some fields, the disease incidence can reach as high as 70%, making it crucial to implement effective prevention and control measures. Below are the symptoms, conditions that favor disease occurrence, and methods for its management.
I. Symptoms
Initially, infected leaves show dark green, water-soaked lesions. These areas gradually contract, causing the leaves to turn yellow and wilt. During wet weather, the lesions become soft and rot, with a grayish mold appearing on the surface. The leaf sheaths develop brown, water-soaked lesions, leading to soft rot and eventual leaf stripping. Infected bulbs and roots also suffer from soft rot, which impairs the plant's ability to absorb and store nutrients, ultimately affecting overall growth and yield.
II. Conditions Favoring Disease Outbreaks
High temperatures and humidity during summer create ideal conditions for disease development. Low-lying fields with poor drainage, weak plant growth, excessive harvesting, and nutrient deficiencies further contribute to severe disease outbreaks.
III. Control Methods
1. Crop Rotation: It is recommended to rotate leek cultivation with non-onion and non-garlic crops for at least three years. This helps break the disease cycle and reduce pathogen buildup in the soil.
2. Land Preparation and Drainage: Level the field and ensure proper drainage systems are in place. After heavy rains, prevent waterlogging by removing puddles and ensuring good water flow.
3. Cultivating Healthy Plants: Select strong seedlings, remove diseased ones, and focus on root development. Avoid over-harvesting, apply top dressing after harvest, and manage irrigation properly during the summer to promote robust plant growth.
4. Pruning and Ventilation: Before the rainy season begins, remove the lower yellow leaves and pick up the green leaves. Secure them with loose grass bark to keep them off the ground, improving air circulation and reducing disease risk.
5. Chemical Control: In mid-July to early August, apply 25% metalaxyl WP diluted at 600–800 times, 64% mancozeb WP at 500 times, or 0.1–0.2% copper sulfate solution through deep irrigation. Applying these treatments directly to the roots or rhizomes has proven to be highly effective in controlling the disease.