Grey mold of leeks is an important disease of leeks in protected areas. In recent years, with the continuous expansion of the cultivation area of ​​leeks in protected areas, the occurrence of grey mold of leeks has gradually increased. The disease is the most serious in March-April, and mild disease fields can reduce production by 10% to 30%, and severe disease fields can reach 60% or more, seriously affecting the yield and quality of leek.
Harmful symptoms
Acinetobacter cinerea is a fungal disease that mainly damages the leaves. The symptoms include white spot, wet rot and dry tip. White point type: White or grayish-brown small spots appear on the front or back of the leaves, resulting in scorching of whole or half leaves. Wet rot type: In the growth period or storage and transportation period, when the humidity is too high, wet rot symptoms often appear. The diseased leaves did not produce white spots, but they gradually rotted and were dark green. The surface of the dead leaves was densely ash to green villous mold with a musty taste. Especially during storage and transportation, the leeks are bundled into bundles, and the speed of mutual contamination and infection increases, causing bundles of leeks to rot into a pile of mud, causing serious economic losses. Dry-tip type: It rots down from the cut edge of the cutting knife, and it is water-stained at the beginning. It becomes light green afterwards and has a brown ring pattern. After the lesion has expanded, it is generally in a “V†shape and can extend downwards by 2 to 3 cm. It is yellow-brown and has gray-brown or gray-green villous fungi on its surface.
Incidence conditions
1. Temperature and humidity conditions Low temperature, high humidity, and insufficient light are the main conditions for the occurrence of gray mold. The temperature is between 15°C and 21°C, and the relative humidity of the air is above 85%. Diseases are easy to spread. When the temperature in the shed is high and low for several consecutive days, it can reduce the resistance of the leeks and cause illness.
2. Cultivation conditions A lot of nitrogen fertilizer, phosphorus and potassium fertilizer deficiency, nutritional incoordination of leek fields, easy to disease. Fields with poor field management, weak leeks, and poor disease resistance are also susceptible to disease. Long-term continuous cropping is conducive to the accumulation of pathogenic bacteria and the incidence is serious.
Hazard characteristics
1. Grey mold of leeks occurs in protected areas, especially in winter and spring. Because of the high humidity and temperature of the greenhouse, and the widespread presence of the pathogen, the gray mold of leek is very easy to occur in the greenhouse, and even the disease is endemic.
2. Fast development. Botrytis cinerea is an outbreak of epidemic disease. When the conditions are appropriate, the gray mold of the leek grows from the point of initial infestation to the spotting. It takes only one day and a few days, and it takes only 2 to 9 days from the occurrence of the spot to the outbreak of the entire greenhouse. Therefore, once the gray mold of leeks is uncontrolled, the whole shed will rot in a few days.
3. Long time of harm. In open field cultivation, leek gray mold is usually limited to late autumn and spring. However, in the sheds, it can be affected all year round. The main damage time is as long as 5 to 6 months. The incidence is most severe in spring, and the occurrence of gray mold of leeks in March to April is the peak period of pandemic. .
Comprehensive measures
1. Increase farm manure and phosphorus and potassium fertilizers. Since there is sufficient nitrogen fertilizer to produce high yields of amaranth, people often use large amounts of ammonia-containing urea and ammonium nitrate. Practice has proved that a large number of single application of nitrogen fertilizer is also an important condition for the initiation of gray mold. Therefore, in the application of nitrogen fertilizer, phosphorus and potassium should be applied together. For example, diammonium 15-20 kg per acre, potassium sulfate 20-25 kg (or 50 kg of vegetation ash), while the application of decomposed farmyard fertilizer 10-15 cubic meters, which is the material basis for the prevention of gray mold occurrence of high yield.
2. Control temperature and humidity. According to weather conditions, open a certain amount of greenhouse film at noon for ventilation cooling and dehumidification. Through ventilation regulation, the maximum temperature in the shed is less than 25°C, the temperature difference between day and night does not exceed 10°C, and the relative humidity in the shed is controlled below 70%. Note that an apron should be added to the bottom of the shed and it is forbidden to vent from the bottom.
3. Clean up old leaves. When harvesting leeks, they must take all the excised parts out of the shed, and then clean up the tying. For the cleaned sick leaves and old leaves, they must be buried deep.
4. The rotation is down. Severe disease fields should be rotated for 2 to 3 years with cruciferous, gourd, and other vegetables. They must not be rotated with onions and garlic.
5. Drug control. First, spray control was performed after each harvest. Can use 50% fasting WP 1200 times, or 50% acetaminophen WP 1000 times, or 50% carbendazim wettable powder 600 times spray control, spray every 7 to 10 days , Even spray 2 or 3 times, the control effect is better. Followed by the beginning of the disease, use 10% fast Ke Ling smoke agent or 45% chlorothalonil smoke agent smoke control. 250-300 grams of smoke agent per acre, divided into 8 to 10 points, with dark fire smoked 3 to 4 hours, the control effect is obvious.
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