Tomato late blight is a low-temperature, high-humidity disease. The temperature in the greenhouse is 22-24°C during the day and 10-13°C at night. The relative humidity of the air is more than 80% to infect the plants, especially in the rain and light. Conditions are more susceptible to epidemics. At present, the tomato cultivated in winter and early spring in our province is in the seedling stage, and the low-temperature period is vulnerable to late blight. It needs to pay attention to the prevention and treatment of diseased plants as soon as possible.
It is understood that tomato late blight, also known as tomato disease, leaves, stems, fruit can be affected, with serious damage to the leaves and green fruit. Leaf victim usually begins with the tip or leaf margin of the middle and lower leaves, and then gradually spreads to the upper leaves and fruits. The initial stage is dark green irregular water-stained lesions. There is no clear boundary between disease and health. It is prone to occur when the air is wet, and the lesions spread rapidly, with a layer of white mold on the edges of the lesions on the back of the leaves. When the air was dry, the lesions were green-brown and then dark brown and gradually dried off. The stalk was damaged, the diseased part was water-stained, and it sag slightly downwards and then became brown. The diseased stem tissue became soft, the plants wilted, and the severe diseased part was broken, causing the stems and leaves to die. The victims suffer from fruit disease. The lesions begin to appear on the fruit surface near the fruit stalk. The lesions are inconspicuous with large spots of oily stains. They gradually develop into four weeks and gradually turn dark brown later. The lesions are slightly sunken and the disease is hard and soft. Corruption does not turn red at the periphery, and a layer of white mold is produced on the surface of the lesion when wet. After the fruit is harvested, it will continue to suffer during storage, transportation and sales, and it will be destroyed in large quantities.
The late blight of tomato is caused by the infection of Phytophthora. The pathogens mainly overwinter in tomato and potato tubers cultivated in winter and spread to the tomato plants through airflow or rain. The occurrence and epidemic of the disease are greatly influenced by species, pathogenic bases and meteorological conditions, among which meteorological conditions predominate and once the conditions are right, the epidemic will soon occur. At present, more cooperation in the province's cultivation 903, Chaoyan 219, Jinteng No. 1, R-304, Zhejiang powder 202, Su powder No. 8, Su powder No. 9, Jiang vegetables No. 14 and other varieties are not resistant to disease, which is caused by One of the reasons for the heavier incidence of tomato late blight. In addition, the disease can still occur in large quantities after frost, and the formation of water film and frost damage during frost formation is conducive to the invasion of bacteria, and the occurrence of late blight after frost is more serious.
At present, the main control water segment of tomato late blight is still chemical control. Since the beginning of the disease, the use of fast speed net 52.5% ketoxime urea cyanide WP 2000 times, or 50% enoyl EDP wettable powder 600 times, or EKL 72% urea MnZn WP 600 times the liquid, or Amisida 250 g / l azoxystrobin suspension 1500 times spray, every 7 to 10 days once, continuous control of 3 to 4 times, can effectively control the hazards of the disease. In addition, through rational rotation, selecting disease-resistant varieties, disinfecting seeds and seedbeds, and strengthening cultivation and management measures can mitigate the hazards.
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