Regulate the temperature, light, water, fertilizer and vegetables with less diseases.

Although chemical control is an important means to control diseases, if the occurrence of diseases is restrained by various physical control measures, the application amount of chemicals can be reduced and the safety of vegetables can be improved. From a physical point of view, it is an important measure to control the occurrence of diseases by regulating the temperature, light, water and fertilizer in the greenhouse and inhibiting the spread and infection of pathogens. Temperature pathogens have a certain suitable temperature for the disease, beyond this temperature range, the infection of pathogens will be inhibited, or even killed. Fungal pathogens are generally sensitive to high temperature and insensitive to low temperature. At low temperature, pathogenic spores can survive longer, while at high temperature, pathogens are quickly killed. Some temperature-loving vegetables have good tolerance to high temperature, such as cucumber has the strongest photosynthesis under the condition of 38 ℃ and high humidity. Therefore, when the humidity in the greenhouse is high and sunny, closing the vents at noon and raising the temperature in the greenhouse to 40 ℃ for 2 hours can well prevent the occurrence of cucumber diseases. Ultraviolet light in sunlight has a strong killing effect on pathogens, and strong light, sufficient photosynthesis of plants, sufficient photosynthate, strong stress resistance of plants, pathogens are more difficult to infect. The effect of light on plant growth is obvious. When the light is weak in overcast and rainy weather, the disease is most likely to break out. The light also directly determines the change of temperature in the shed. Moisture (humidity) under normal circumstances, the light and temperature in the shed are mainly determined by the external environment. Such as continuous rainy days, the light and temperature can not be high. At this time, water has become the key factor affecting the epidemic of the disease. High humidity is beneficial to the infection and spread of pathogens. Outbreaks of most diseases require more than 85% relative humidity. The humidity in the shed is affected by irrigation, ventilation and other factors. Among them, ventilation is the most important factor affecting the humidity in the shed. Under general conditions, the humidity inside the shed is much higher than that outside the shed. If the ventilation condition is good, the air inside and outside the shed will circulate, and the humidity inside the shed will decrease. The pathogen needs a long time and high humidity to complete the infection hazard process. Many vegetable farmers ventilate the breeze for 10 to 20 minutes after uncovering the grass. The very important purpose is to quickly reduce the humidity in the shed, reduce the dew time on the surface of vegetables, and inhibit the infection of pathogens. The water use efficiency of traditional irrigation is low, which has a great influence on the humidity in the greenhouse, while drip irrigation can greatly improve the water use efficiency, reduce the evaporation of surface water and control the humidity in the greenhouse. Plastic film mulching directly reduces the contact area between the surface and the air and reduces the evaporation of surface water. Humidity is greatly affected by temperature. When other conditions remain the same, the higher the temperature, the smaller the humidity. Fertilizer is the "food" for plant growth. The amount and proportion of soil fertility determine the development of plants. If the plant is underdeveloped, the disease resistance is poor.