How to prevent and control cucumber downy mildew? The latest technical method tutorial is here

Cucumber downy mildew is the most common and most serious disease in protected cucumber cultivation, commonly known as "running horse dry" or "dry leaves", etc. Both seedlings and mature plants can be affected, damaging leaves and stems, with tendrils and flower stalks less affected. The disease comes on fiercely, causes severe infection and spreads quickly. If not controlled in time, it will cause devastating losses to cucumbers. Let's take a look at cucumber downy mildew prevention and control techniques together below!

Symptoms of cucumber downy mildew

Cucumber downy mildew mainly occurs on the leaves. When the disease occurs at the seedling stage, chlorotic spots first appear on the cotyledons, gradually becoming yellow irregular spots. When humid, a grayish-black mold layer forms on the underside of the cotyledons. As the disease develops, the cotyledons quickly turn yellow and dry up. When the disease occurs at the mature plant stage, light green water-soaked spots first appear on the leaves. After expanding, they are limited by the leaf veins and become polygonal, turning from yellow-green to light brown. In the later stage, the lesions merge into patches, the whole leaf dries up, and the leaf margins curl upward. When humid, a grayish-black mold layer grows on the lesions on the underside of the leaves. In severe cases, the leaves of the whole plant die. On disease-resistant varieties, the lesions are fewer and smaller, and the mold layer on the leaf underside is also sparser.

Causes of cucumber downy mildew

1. Pathogen: The pathogen of cucumber downy mildew is Pseudoperonospora cubensis, belonging to the genus Pseudoperonospora, subphylum Mastigomycotina. The sporangia of this pathogen are spread by airflow and rainwater. In greenhouses, human production activities are the main source of downy mildew infection. The most suitable temperature for cucumber downy mildew is 16-24°C. Below 10°C or above 28°C, it is harder for the disease to occur; below 5°C or above 30°C, it basically does not occur. The suitable humidity for the disease is above 85%, especially when there is a water film on the leaves, it is most susceptible to infection. When humidity is below 70%, the pathogen spores have difficulty germinating and infecting; below 60%, the pathogen spores cannot be produced.

2. Spread: The pathogen overwinters in protected areas and spreads the following spring. It can also spread from the south with the monsoon. In summer, it can spread through airflow and rainwater. In the north, cucumber downy mildew spreads from greenhouses to plastic tunnels, then to spring open-field cucumbers, then to autumn open-field cucumbers, and finally back to greenhouse cucumbers.

3. Pattern: The pathogen is an obligate biotrophic parasitic fungus. Seeds do not carry the pathogen. The pathogen mainly spreads by airflow and invades through leaf stomata. The occurrence of downy mildew is very closely related to the temperature and humidity environment around the plant. The initial temperature for occurrence is about 16°C, while the suitable temperature for an epidemic is 20-24°C, and it requires relative humidity above 85%. The disease spreads very quickly. Some people call it "running horse dry". Once there is a central diseased plant, only 3-4 rounds of expanded secondary infection are needed to cause a major disaster. Therefore, the key to controlling this disease is to discover the central diseased plant or disease area as early as possible.

Cucumber downy mildew prevention and control techniques

1. Disease-resistant varieties: Cucumber varieties differ greatly in resistance to downy mildew, so choose relatively resistant varieties.

2. Disease-free seedlings: Isolate the cucumber seedling-raising area from the production area, and strictly discard diseased seedlings when transplanting.

6. Site selection: When cultivating cucumbers in the open field, choose plots with higher terrain and good drainage for planting.

4. Ecological control: Reform cultivation methods, improve the ecological environment, implement plastic film mulching, reduce soil moisture evaporation, lower air humidity, and increase soil temperature. Carry out subsurface irrigation under the film, water in the morning on sunny days, and strictly prohibit watering on cloudy and rainy days to prevent excessive humidity and leaf condensation. After watering, remove moisture in time to prevent leaf condensation at night. Strengthen temperature management. In the morning, control the greenhouse temperature at 28-32°C, with a maximum of 35°C, and air relative humidity at 60-70%. Do not ventilate too early every day.

5. Scientific fertilization: Apply sufficient base fertilizer. During the growing period, do not apply too much nitrogen fertilizer. Shuangbeier, to improve the disease resistance of the plants. 70-100 ml plus 15 ml garlic oil plus 25 ml Wofengsu plus organosilicon, diluted with 30 jin of water, spray continuously 2-3 times. After control, switch to prevention. Plant disease is often related to an imbalance in the "carbon-nitrogen ratio" in the plant body. When the carbon content is relatively low, the disease is more likely to occur. Based on this principle, increasing the carbon ratio through foliar spraying can improve the disease resistance of cucumbers.

6. High-temperature greenhouse sealing: Generally, close the greenhouse tightly at noon for two hours, so that the temperature of the upper part of the plants reaches 44-46°C, not exceeding 48°C. This can kill the downy mildew pathogen in the greenhouse. Carry it out once every 7 days. After 2-3 times, the development of the disease can basically be controlled.