Control techniques of cucumber downy mildew

Cucumber downy mildew is the most common and serious disease in cucumber cultivation in protected areas, commonly known as horse dry, dried leaves, etc., adult plants can be injured at seedling stage, and damage leaves and stems, tendrils and pedicels suffer less, the disease is fierce, the disease is serious, and spreads fast. if not timely control will cause devastating losses to cucumbers, let's take a look at cucumber downy mildew control techniques!

Symptoms of cucumber downy mildew

Cucumber downy mildew mainly occurs on leaves. At the seedling stage, chlorotic spots appeared on the cotyledons at first, and gradually showed yellow irregular spots. When the cotyledons were wet, there was a gray-black mildew layer on the back of the cotyledons. With the development of the disease, the cotyledons quickly turned yellow and withered. When the disease occurs in the adult stage, light green water immersion spots appear on the leaves, and after expansion, they are polygonal and yellowish green turn to light brown. In the later stage, the disease spots converge into a piece, the whole leaf is dry, curling upward from the leaf margin, and a gray-black mildew layer appears on the disease spot on the back of the leaf when it is wet, and when it is serious, the leaves of the whole plant die. The disease spots of resistant varieties are few and small, and the mildew layer on the back of leaves is also sparse.

Etiology of cucumber downy mildew

1. The pathogen of cucumber downy mildew: the pathogen of cucumber downy mildew is pseudodowny mildew of Cuba, whose sporangia are transmitted by airflow and Rain Water. In the greenhouse, people's production activities are the main source of infection of downy mildew. The most suitable temperature for cucumber downy mildew was 16: 24 ℃, lower than 10 ℃ or higher than 28 ℃, and less than 5 ℃ or more than 30 ℃. The suitable humidity of the disease is more than 85%, especially when there is a water film in the leaves, it is most vulnerable to infection. When the humidity is less than 70%, it is difficult for bacterial spores to germinate and infect, and less than 60%, bacterial spores cannot be produced.

2. Transmission: the pathogen overwinters in the protected area and spreads in the next spring. It can also spread from the south with the monsoon. Summer can be spread by airflow and Rain Water. In the north, cucumber downy mildew spread from greenhouse to greenhouse, then to cucumber in open field in spring, then to cucumber in open field in autumn, and finally to cucumber in greenhouse.

3. The law: the pathogen is a living parasitic fungus, the seed does not carry bacteria, and the pathogen is mainly transmitted by airflow and invades from the stomata of leaves. The occurrence of downy mildew is closely related to the temperature and humidity environment around the plant. The initial temperature is about 16 ℃, while the suitable temperature for epidemic is 20-24 ℃, and the relative humidity is more than 85%. The spread of the disease is very fast, and some people call it Happy Horse Gan. Once there is a central disease plant, it only needs 3 or 4 times of expansion and re-infection, which can lead to a major disaster, so the key to the prevention and treatment of the disease is to find the central disease strain or disease area as soon as possible.

Control techniques of cucumber downy mildew

1. Disease-resistant varieties: cucumber varieties have different resistance to downy mildew, so the varieties with more disease resistance should be selected.

2. Disease-free seedlings: cucumber seedlings are isolated from production areas, and diseased seedlings are strictly eliminated during planting.

6. Garden selection: when cucumber is cultivated in open field, the plots with high terrain and good drainage should be selected for planting.

4. Ecological prevention and control: reform farming methods, improve ecological environment, implement plastic film mulching, reduce soil water evaporation, reduce air humidity, and increase ground temperature. Undercover irrigation under the film, watering in the morning on sunny days, watering on rainy days is strictly prohibited to prevent excessive humidity and leaf dew. Remove moisture in time after watering to prevent foliar condensation at night. Strengthen temperature management, control the temperature of the shed at 2832 ℃ in the morning, the highest 35 ℃, air relative humidity 60% 70%, do not let out prematurely every day.

5. Scientific fertilization: apply sufficient base fertilizer, do not apply too much nitrogen fertilizer during the growing period, and frost bell to improve the disease resistance of the plant. 70 kilogrammes 100 milliliters plus 15 milliliters of garlic oil plus 25 milliliters of Gavofengsu plus 30 jin of silicone mixed with water for 2 times, then changed to prevention after control. The disease of plants is often related to the imbalance of carbon-nitrogen ratio in plants, and it is easy to occur when the content of carbon is relatively low. According to this principle, the disease resistance of cucumber can be improved by spraying fertilizer on the leaf and increasing the proportion of carbon elements.

6. High temperature greenhouse: generally seal the greenhouse for two hours at noon, so that the upper temperature of the plant reaches 44-46 ℃, not more than 48 ℃, which can kill the downy mildew in the greenhouse, once every 7 days, 2-3 times, can basically control the development of the disease.