The latest course on prevention and control of cucumber downy mildew

Cucumber downy mildew is the most common and most serious disease in cucumber cultivation in protected areas, commonly known as horse stem, dry leaves, etc., seedling stage adult plants can suffer, damage leaves and stems, tendrils and pedicels suffer less, the disease is fierce, the disease is serious, and the spread is fast. If it is not controlled in time, it will cause devastating losses to cucumber. Let's take a look at the control technology of cucumber downy mildew.

Symptoms of cucumber downy mildew

Cucumber downy mildew mainly occurs on leaves. At seedling stage, chlorosis spots appeared on cotyledons at first, and gradually yellow irregular spots appeared. When wet, gray black mold layer appeared on the back of cotyledons. With the development of disease, cotyledons quickly turned yellow and withered. At the mature stage, light green water spots appear on the leaves at the beginning of the disease. After expansion, they are restricted by the veins and are polygonal. Yellow-green to light brown. At the later stage, the disease spots converge into pieces. The whole leaves are dried up and curled upward from the leaf edge. When wet, gray black mold layers appear on the disease spots on the back of the leaves. When serious, the whole leaves die. The disease spots of resistant varieties were few and small, and the mold layer on the back of leaves was sparse.

Pathogenesis of cucumber downy mildew

1. Pathogen: The pathogen of cucumber downy mildew is Pseudoperonospora cubana, a subphylum of flagellates. The sporangia of the pathogen are transmitted by air current and rain. In greenhouses, people's productive activities are the main source of downy mildew infection. The most suitable temperature for cucumber downy mildew was 16~24℃, lower than 10℃ or higher than 28℃, the disease was difficult to occur, lower than 5℃ or higher than 30℃, the disease basically did not occur. The suitable humidity for the disease was above 85%, especially when the leaves were covered with water film. When humidity is lower than 70%, spores are difficult to germinate and infect, and when humidity is lower than 60%, spores cannot be produced.

2. Transmission: The pathogen overwinters in the protected area and spreads in the next spring. It can also be transmitted from the south with the monsoon. In summer, it can be transmitted by airflow and rain. In the north, cucumber downy mildew is transmitted from greenhouse to greenhouse, then to spring open field cucumber, then to autumn open field cucumber, and finally back to greenhouse cucumber.

3. Law: The pathogen is a living, obligate parasitic fungus, the seed does not carry bacteria, the pathogen mainly spreads by air flow, and invades from the stomata of the leaves. The occurrence of downy mildew is closely related to the temperature and humidity around the plant. The initial temperature of downy mildew is about 16℃, while the optimum temperature for epidemic is 20~24℃, and the relative humidity is above 85%. Once there is a central diseased plant, it only needs 3~4 times of expanded reinfection to cause a major disaster. Therefore, the key to prevent and control this disease is to find the central diseased plant or disease area as soon as possible.

Control techniques of cucumber downy mildew

1. Resistant varieties: cucumber varieties have great differences in resistance to downy mildew, so it is necessary to select more resistant varieties.

2, disease-free seedlings: cucumber nursery and production isolation, strict elimination of disease seedlings when planting.

6. Garden selection: When cucumber is cultivated in the open field, it is necessary to choose a plot with higher terrain and good drainage.

4. Ecological control: reform farming methods, improve ecological environment, implement plastic film mulching, reduce soil moisture evaporation, reduce air humidity, and increase ground temperature. Under-film dark irrigation, watering in the morning on sunny days, watering in rainy days is strictly prohibited to prevent excessive humidity and dew condensation on leaves. Remove moisture in time after watering to prevent dew on leaves at night. Strengthen temperature management, control the temperature of the shed room at 28~32℃ in the morning, the highest temperature is 35℃, the relative humidity of the air is 60~70%, and do not let out the air too early every day.

5, scientific fertilization: apply enough base fertilizer, growth period do not apply too much nitrogen fertilizer, frost bell to improve the disease resistance of plants. 70~100 ml garlic oil 15 ml plus 25 ml plus Wofengsu silicone mixed with water 30 jin continuous spray 2~3 times, after control changed to prevention. The disease of plants is often related to the imbalance of "C/N ratio" in their bodies, and the disease is easy to occur when the carbon content is relatively low. According to this principle, the disease resistance of cucumber can be improved by spraying fertilizer on leaves and increasing the proportion of carbon element.

6, high temperature stuffy shed: generally at noon closed shed for two hours, so that the upper temperature of the plant reached 44~46℃, do not exceed 48℃, can kill the frost mold in the shed, once every 7 days, 2~3 times, can basically control the development of the disease.