The vegetable cultivation in the greenhouse is carried out in the environment of artificial facilities, which is fundamentally different from the unfavorable conditions of open cultivation. It is not only beneficial to the annual production and supply of vegetables, but also provides good conditions for the occurrence of diseases and insect pests. With the rapid development of greenhouse cultivation, the types of pests and diseases have been significantly increased, and the degree of harm has increased significantly, and the source of bacteria and insects has been provided for exposed vegetables. 1, the impact of soil on pests and diseases Soil is the root environment of vegetables, but also a variety of pathogenic wintering sites. Under normal conditions, the pathogens in the soil maintain a certain balance with a large number of beneficial microorganisms. The types of vegetables cultivated in greenhouses are relatively simple, the cultivation area is limited, and rotation is difficult. Continuous cropping is inevitable. Due to the residual substances and roots of vegetable roots, the soil microorganisms gradually lose their balance, and the number of pathogens continues to increase, which induces diseases. The soil in greenhouses is less exposed to exposed soil, higher in temperature and humidity, the rapid proliferation of pathogens, and the lack of disease-resistant varieties in production. Soil-borne diseases are aggravated by continuous cropping years. For example, if a new greenhouse occurs, the occurrence of melon wilt disease is not timely. Take effective control measures, generally only four to five years from the sporadic disease to change the incidence. In the large-scale multi-span greenhouses, the root-knot nematode disease of fruit vegetables only takes 3 to 4 years, the diseased plant rate can reach 100%, and the output is reduced by more than 50%, which seriously threatens the production of various vegetables. In recent years, there have been similar reasons for the expansion of Solanum oleracea wilt and the distribution of Verticillium wilt disease in eggplant and the intensification of damage. A variety of pathogenic bacteria overwintered with the diseased body in the soil and became the primary infestation source in the following year. It is an important link in the occurrence of vegetable diseases. The death rate of pathogenic bacteria in open field is high, and it can be infected in the growing season of vegetables. The incidence is late and the damage is light. Some diseases only occur seasonally in local areas. Under the cultivation of greenhouses, pathogens can safely pass through the winter, and can also occur in the anniversary, and have become the enemy of the development of greenhouse vegetable production. Such as melon anthracnose, bacterial angular spot, blight, cucumber, sweet pepper, leek disease, tomato early blight, leaf mold, cowpea and bean rust, black spot disease, celery spot blight, a variety of Vegetable sclerotia, gray mold and so on. In addition, pathogens causing damping-off of rice seedlings and blighting can both survive winters in the soil, and they can also live in rot. Therefore, they often occur in seedbeds of old-style breeding seedlings, or even destroy seedlings and delay farming. Underground pests such as earthworms and cockroaches also occur early, in large quantities, and in severe damage due to the warm, moist, loose and fertile soil in greenhouses and nursery houses. 2, the impact of air humidity on the disease in the greenhouse in the cold season, closed insulation at night, the relative humidity of the air up to 90% -100%, greenhouse roof, wall condensation can be scattered on the plant. Cucumbers, tomatoes and other vegetables have large heat capacity, and leaves and fruits can form water films, creating a high-humidity environment. They are not able to grow and develop vegetables, and their disease resistance is reduced, but they are suitable for the germination and infestation of many pathogenic fungi and bacteria. Reproduction. Cucumber downy mildew must be condensed on the leaves for more than 3 hours to germinate and invade the host. Once the disease occurs, it spreads and spreads rapidly, often causing an epidemic, resulting in reduced production or even no harvest. The diseases listed above are aggravated and are closely related to the high-humidity environment. 3. Effect of temperature on pests and diseases The results of long-term co-evolution of vegetables and pathogens, the temperature environment suitable for the growth of vegetables, usually can cause disease, warm conditions in greenhouses, and generally do not become the limiting factor in the occurrence of disease, pests and mites belong to In a type of temperature-changing animal, the ambient temperature directly affects their body temperature and their life activities. The influence of temperature on pest distribution areas and the occurrence of damage is more important than humidity. Greenhouse whitefly can not live in open field in the cold regions of the north. Since the 1970s, with the increase in the area of ​​greenhouses, it can continue to breed in winter greenhouses and form the base of insects, which has become the main pest of vegetables. There is also a similar development process in the tea plant. The Gualou, Myzus persicae, and Red bee spiders can survive winters in open fields, and they can continue to breed in the greenhouses. Their occurrence is on the rise. 4. Effect of host on disease occurrence Tomatoes infected with Phytophthora infestans only infected tomato and potato. Before the 1970s, the bacterial source of exposed tomato was from potato. The northern vegetable region occurred only when the meteorological conditions were appropriate in individual years, and the harm was minor. With the rapid increase of greenhouse tomato cultivation area in autumn and winter, the disease has been increasing year by year, and it has also provided a large number of bacterial sources for exposed tomatoes, which has become one of the major diseases of the year. The pastoral epidemics of tomato in the Beijing suburbs from 1979 to 1987 were a few pandemics, of which the large number of bacterial sources in the greenhouse was an important reason. In the 50-60s, cucumber downy mildew was the main disease of greenhouse cucumber in winter and spring. After the 1970s, it was cultivated with the greenhouse. The cucumber and other melon vegetables were planted all year round, and the disease source gradually increased, which made the disease become The most extensive and most harmful diseases. The impact of the development of greenhouse vegetable cultivation on the dynamics of pests and diseases is the result of people’s production activities. Blind introduction and planting in production can directly cause dangerous diseases to spread and spread. For example, cucumber black spot pathogens occur sporadically in the northeast, but in the past few years, they have been devastated in 26 cities and cities in 3 northeastern provinces. The loss in serious disease sheds has reached more than 70%, and serious seedling stage has caused the destruction of seedlings and the outbreak of production. At present, Shandong, Hebei, Shanxi, Inner Mongolia, Beijing, and Hainan have occurred in 6 provinces and there is a tendency to spread out. However, the environmental conditions in the greenhouse are not conducive to the occurrence of various pests and diseases. Virus disease in vegetables is a type of disease that is common, serious, and difficult to control. In greenhouses, tomatoes, sweet peppers, and winter spinach vegetables are most commonly found in summer and autumn, and the degree of damage is generally lower than that of open field cultivation in the same period. Zucchini cultivation in the greenhouse in the spring, when the summer season virus season prevalence of the virus has been basically harvested, as long as the current prevention and control work, compared with open cultivation of the disease and cut significantly reduced.
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