In winter and spring sheds, leeks often show some symptoms such as dry tips, root rot, dead leaves, and rot of stems and leaves. However, the same causes of symptoms are not necessarily the same. Correctly determining the cause of the symptoms and taking effective preventive measures in time is the key to cultivation.
A dry tip
1. Acidification of the soil. The long-term heavy application of manure, cake fertilizer and other acidic fertilizers will cause acidification of the soil and cause acid hazards. The performance is that the temporal lobe grows slowly, is weak, and the outer leaves are yellow.
Control methods: Apply enough compost as base fertilizer and lime to adjust soil pH. However, lime cannot be used in the greenhouse to avoid ammonia volatilization.
2. Caused by toxic gas hazards. Applying large amounts of sodium bicarbonate in front of the shed, or applying sodium bicarbonate after baiting, spreading urea and cottonseed cake on the ground, and applying ammonium sulphate on soils with high lime content may cause excessive accumulation of ammonia in the greenhouse. As a result of ammonia damage, the tip of the leaves will gradually turn brown. If the soil has been acidified, it may be caused by the accumulation of nitric acid gas.
Control methods: Fertilizers should not be applied before or after the shed to produce ammonia that can produce ammonia directly or after decomposition.
3. Caused by high temperatures. The suitable temperature for the growth of leeks is 5°C～35°C, and the temperature is above 35°C for a long period of time. After a sudden clearing after yin, or sudden intrusion of cold wind after high temperature, it may cause leaf to dry.
Control methods: timely ventilation, timely watering, increase nitrogen fertilizer, enhance the heat-resistant capacity of leeks.
4. Lack or excess of trace elements. Ca deficiency in the center of the yellow leaves, some dead leaves tip; lack of magnesium caused by external leaves yellowing and dead; lack of boron in the center of yellow leaves, physiological obstacles; excess boron, usually from the tips of the leaves withered; excessive use of manganese-containing pesticides, causing excess manganese At the time, the leaves were slightly yellowed and the outer leaves yellowed and died.
Control methods: The application of trace element fertilizers outside the root can relieve symptoms partially or completely.
Second, dead plants
1. Root rot caused death. There are three kinds of deaths caused by the root rot of leeks: (1) Asphyxial root rot, the excrement of livestock and poultry or other debris in Putian, causing local high temperatures, causing the roots of oysters to breathe anaerobicly, causing lactic acid and ethanol poisoning. (2) Water icing causes root rot. Improper freezing of water caused by the freezing of water in the area, the freezing and thawing alternate root damage or low-temperature flooding caused the roots to die. (3) Watering with contaminated water or pit water will cause the soil to be destroyed or direct poisoning to death.
Control methods: keep Putian clean and avoid accumulation of debris; timely watering, avoid freezing injury; do not use polluted water irrigation.
2. Earthworms cause the death of roots.
Control methods: If a large amount of earthworms or cockroaches are found in the soil around the roots and around 10 centimeters, it can be controlled by pungent, pungent, chlorpheniramine, and other pollution-free drugs.
Third, stem and leaf rot
1. Diseases. At the time of onset, an immersed dark green lesion was formed from the lower part of the leaf, and when it expanded to half of the leaf, the whole leaf turned yellow and wilted. After greenhouse leeches, if the humidity is high, the disease often occurs.
Control methods: Level land and dig up drainage system. In the early stage of disease, 25% Rhodospermae Mildiorrhizae 1000 times or 75% Chlorothalonil 500 times was used to irrigate the roots. Each cavity was filled with 250 ml, and then irrigation was performed 10 days later.
2. Gray mold. At the beginning of the disease, the leaves produce gray-brown or white spots. Afterwards, the lesions expand. The tip of the leaf begins to grow rot and dry, and when the humidity is high, a gray villous mold layer is produced. High humidity is the main cause of the disease, and the relative humidity is more than 85%. High-temperature, high-humidity leeks grow fast, have poor resistance to diseases, and have a large temperature difference between day and night, or the leeks on the bottom of the leeks are frozen and have serious morbidity.
Control methods: (1) Select resistant varieties. (2) Strengthen ventilation and reduce humidity. (3) Chemical control. Before the onset of illness, 200 grams of chlorothalonil fumigant per acre was used to disperse into 6-8 spots. After being ignited with dark fire, the shed was closed, and after 7-8 days, it was smoked again. Can also be used at the beginning of the disease with 50% carbendazim or 70% thiophanate 500 times, sprayed once every other week, and even spray 3 to 4 times.
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