In late winter and early spring, low temperatures and low temperatures are the norm. At present, overwintering tomatoes and other fruits have begun to enter the fruit-setting period in most areas, and the early batch of eggplant fruits and vegetables in spring has also begun to enter the transplanting period. Affected by unfavorable weather, the overall growth of vegetables in greenhouses is generally weak in winter. In addition, the light intensity is low, the photosynthesis of crops is low, and the ability of flowering and fruiting such as tomatoes is reduced. Increased humidity in some greenhouses is likely to cause a high incidence of vegetable gray mould and other diseases, which urgently need to be paid attention to.

1. Tomato gray mold
Tomato gray mold is one of the most common diseases in greenhouse cultivation in winter. Gray mold infects tomato leaves, stems, flowers and fruits, but it is considered to be more serious to green fruits. Infected leaves, mostly from damaged leaves or long-term condensed leaf tips or leaf edges, spreads inward in a "V" shape, initially water-stained, and then develops into yellowish brown with concentric ring spots. . Stem infections usually infect from the pruning place. When the environment is humid, a gray mold layer will be produced. If it is not removed in time, it will spread to the stems and become infected, causing plant necrosis. It is onset at flowering or after fruit setting. It usually invades from the remaining stigma or broken petals, and infects the fruit or stalk along the petals, causing the stalk to form gray-brown necrotic spots. When the air is humid, the diseased fruit rots and produces thick gray Mold layer, resulting in a large reduction in production.

2. Tomato malformed fruit disease The main causes of tomato malformed fruit are: low temperature, insufficient light, poor management of fertilizer and water, improper use of plant growth stimulators, resulting in imbalance of root-shoot ratio, insufficient development of flowers and fruits, and appearance of spires and deformities; Or too much nutrient is transported to the differentiation of flower buds, causing the flower bud cells to divide too prosperously, and the number of tomato ventricles increases, thus forming a multi-ventricle malformed fruit; or tomato fruit pedicle to fruit umbilical cork bridge line, in the soil moisture In the case of increased height, the fruit will crack from the position of the bridging line to form a zipper fruit.

Tomato late blight When the leaves are infected, the pathogens usually invade from the tip or the edge of the leaf. At first, they appear as small gray-green spots, then become irregular dark-green water-stained spots, and finally turn brown. When the temperature and humidity are appropriate, a white mold layer will be formed at the junction of disease and healthy leaves. When the petiole and stem are infected, brown irregular necrotic spots are formed, and the surface of the diseased part is rough. Fruits in the green fruit stage are prone to disease, irregular brown necrotic spots are formed on the surface of the fruit, and a white mold layer is produced when the air is humid.

3. Cucumber sclerotinia disease When the humidity in the greenhouse is higher than 85%, it is conducive to the onset of sclerotinia disease. The young melons and stems in the lower part of the plant often get serious. Young melons are infected, mostly starting from the top. At first, they are water-spotted and dark green rot, and then dense flocculent white mold is produced in the diseased area. When environmental conditions are suitable, the diseased white mold turns into black rat fecal sclerotia. The stems were damaged and began to produce fading water-soaked disease spots, then softened and rotted, the diseased parts produced white flocculent hyphae, and then formed black rat fecal sclerotia, causing the infected parts of the plants to die.

4. Cucumber downy mildew Cucumber downy mildew mainly occurs on the leaves. The diseased leaves are light green water-soaked spots at the beginning, and are restricted by the veins after they are enlarged. They are polygonal, yellow-green to light brown, and later the diseased spots merge into pieces. The leaves are dry. When the leaves are wet, a gray-black layer of mildew develops on the diseased spots on the back of the leaves.

Prevention method
During continuous rain or haze, watering or spraying must not be used to prevent tomato gray mold to prevent the humidity in the greenhouse from increasing again. It is necessary to ensure the temperature in the greenhouse while ventilating at the same time. After the tomatoes have set fruit, remove the stigma in time to prevent infestation of the fruit. To prevent and control tomato malformed fruits, the light and temperature and humidity in the shed during the seedling period should be controlled. The temperature in the shed should be kept at 20℃~25℃ during the day and 10℃~17℃ at night. Strengthen field management, avoid increasing the incidence of deformed fruits due to excessive nitrogen and water in the soil, and control the amount of nitrogen fertilizer and watering during the nursery period.

Tomato late blight can infect tomato stems, leaves, and fruits. To prevent tomato late blight, avoid excessive humidity in the shed for a long time, timely ventilation, timely removal of diseased plants in the early stage of the disease, and timely drug control. When the seedlings grow excessively after planting, ventilation should be strengthened, humidity should be controlled reasonably, plant growth regulators should be sprayed appropriately, and the growth regulators should be prevented from being sprayed on the plant growth points by mistake.

The prevention and control of cucumber downy mildew can take advantage of the enclosed characteristics of the protected area to create a high temperature and low humidity environment. Before the continuous haze and rainy weather arrives, spray protective medicine or chemical fumigation method to play a preventive effect.