The celery leaf spot, also known as late blight or "fire dragon," is a common and serious disease that affects celery crops in northern greenhouse areas. It significantly impacts both the yield and quality of the crop. In this article, we'll discuss the symptoms of the disease and provide effective prevention and control methods.
First, let's look at the symptoms. The disease primarily affects the leaves, followed by the petioles and stems. Older leaves are usually the first to show signs, starting from the outer parts and moving inward. Initially, the lesions appear as small, light brown, oily spots with clear edges. As the disease progresses, these spots become irregular in shape, turning from pale yellow to grayish white. The edges often take on a dark reddish-brown color, and small black specks may gather around the lesions. A yellow halo often surrounds the affected area. On the petioles and stems, the lesions appear as brown, slightly sunken areas with scattered black dots in the center. When the infection becomes severe, the leaves may dry out and rot.
Second, understanding the conditions under which the disease occurs is crucial. The celery leaf spot is caused by a fungus and thrives in cool, humid environments. The ideal temperature range for the disease is between 20°C and 25°C, with humidity above 95%. Cloudy weather, frequent temperature fluctuations, high daytime temperatures combined with nighttime condensation, weak plant growth, improper irrigation, and poor ventilation can all contribute to rapid disease spread.
Third, here are some effective control methods:
1. Balanced fertilization is essential. Apply sufficient organic base fertilizer, and when top-dressing, use phosphorus and potassium fertilizers while limiting nitrogen. Foliar sprays and micronutrients can help strengthen the plants' resistance.
2. Temperature and humidity control are key. During the day, keep the temperature between 15°C and 20°C. If it rises above 20°C, ventilate promptly. At night, maintain a temperature between 10°C and 15°C to reduce temperature fluctuations and condensation. Avoid overwatering and ensure proper drainage.
3. Chemical treatments can be very effective. Use 45% chlorothalonil smoke agent or acetamiprid smoke agent at a rate of 150 grams per acre, dispersed into 5-6 liters of water, and fumigate for one night. Repeat every 10 days. In the early stages of the disease, spray a 70% mancozeb wettable powder solution diluted 600 times, or a 50% carbendazim wettable powder solution diluted 600–800 times. Apply every 7–10 days for 2–3 consecutive times for best results.
4. Remove infected plants promptly. Clear out any diseased plant residues in the greenhouse to prevent the spread of the pathogen.
By following these measures, you can effectively manage celery leaf spot and protect your crop from significant losses. Early detection and timely action are vital in controlling this disease.
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