The hot and rainy season is an environment favorable for the propagation of pests and the spread of diseases. It is often the phenomenon that the rotten fruit of tomatoes is serious, the effect of fighting drugs is not obvious, and the vegetable farmers are suffering. The investigation mainly caused by physiological diseases and pests:
First, physiological diseases
　　 1. Water supply imbalance .
In the period of a large number of results, the outside temperature is significantly increased. Due to the large amount of transpiration of the leaves, the water that should have been transferred to the fruit is taken by the leaves. The osmotic pressure of the leaf cells is higher than the osmotic pressure of the green fruit cells, and the leaves even take water from the fruits. A lot of water loss phenomenon, tissue necrosis, causing rotten fruit.
Control measures: (1) Improve the soil. Selecting tomato with deep soil and strong water retention ability to plant tomato, if the soil is too sticky or excessively sandy, it should be applied with organic fertilizer to improve its permeability and enhance its water retention and fertilizer retention capacity. (2) Balanced fertilization. Avoid applying unfertilized organic fertilizer or inorganic fertilizer to a high concentration to prevent burns to roots. The base fertilizer is mainly composed of decomposed organic fertilizer, combined with 50 kg of calcium phosphate per acre and 50 kg of lime. The amount of organic fertilizer is 3000-5000 kg per mu. Avoid using single-fertilizer. When topdressing, pay attention to the combination of N, P and K fertilizers. N, P and K compound fertilizers should be applied 15-20 kg per mu. (3) Strengthen water management. A balanced supply of water to the tomato plants must be guaranteed.
2. Lack of calcium.
   Tomato photorespiration produces a variety of organic acids, of which oxalic acid can cause poisoning and disease. When the calcium content of the tomato plant is sufficient, the oxalic acid is neutralized by calcium to form calcium oxalate, which can avoid the harm of oxalic acid. When the calcium is deficient, the "umbilical rot" is likely to occur, resulting in rotten fruit.
Second, pests and diseases
1. Fungal infection.
   There are mainly (1) Botrytis cinerea, which causes ash, mycelium or conidia on the diseased body, in the soil or on the surface of the winter, causing gray mold, and the flowering period is the peak of gray mold infection. The rainy day is the most important cause of gray mold, which invades from wounds, aging organs and flower organs, causing rotten fruit. (2) mold, leading to late blight, a gray-green water-soaked hard plate grows on the fruit, the edge is not obvious, and then becomes dark brown. When the humidity is high, a small amount of white mold is produced. The pathogen spreads with the wind, water, and rain. The diseased fruits and plants in the field are not thoroughly cleaned, and the healthy plants are cross-infected. (3) Phomopsis mold, causing brown streak disease, when the fruit is damaged, it begins to produce light brown oval-shaped slightly depressed lesions, which turn dark brown, causing fruit to rot, high temperature and humidity, and rapid expansion.
Control measures: (1) Comprehensive prevention and treatment. Carry out disease-free soil cultivation and strong seedlings, reasonably close planting, strengthen ventilation and light transmission, especially on cloudy days, strict control of irrigation should be carried out. Clean up the sick body in time, remove the diseased fruit leaves, take out the field, concentrate on burning and deep burial. When the whole branch is forked, wash the hands with disinfectant, remove the central diseased plant, and disinfect with the lime. (2) Chemical control. The spray can be mixed with 50% keeling WP, 60% keto-wet WP and 60% chlorpyrifos 800 times solution; 50% lycopene WP, 50% blast, 60% % of metalaxyl · manganese zinc wettable powder 800 times mixed use.
2. Pest hazards. 　
Helicoverpa armigera eats fruits with larvae, and occurs 3-4 generations a year. All generations can harm tomatoes, which is beneficial to high temperature and humidity.
Control measures: The black worms are mainly used to trap and kill adults. The larvae can be sprayed and killed before they are incubated in the second instar. Commonly used agents are 20% sterilized ester emulsifiable concentrate 2000-3000 times, or 50% phoxim emulsifiable concentrate 1000-1500 times liquid.
3. Virus infection.
   Viral diseases are the most common, most harmful, and most difficult to control diseases. In the autumn, the incidence is heavier. The main symptoms are curling leaves, falling buds and falling flowers, and the fruit is painted or rotten. The virus is mostly transmitted by aphids, and the disease is heavier in high temperature and drought.
Control measures: (1) Comprehensive prevention and treatment. Choose disease-resistant and disease-resistant varieties; soak seeds during planting; implement 2-3 years of rotation, clean the pastoral, and timely control aphids. (2) Chemical control. It can be sprayed with 20% of virus A wettable powder 500 times, or 1.5% of phytopathogenic emulsion 500 times solution, or potassium permanganate 1000 times solution, once every 5-7 days, and even sprayed 2-4 times.
　　
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