How to control tomato late blight by infecting the whole tomato plant

Late blight occurs in leaves, stems, fruits and leaves. Most of the disease spots start from the tip or edge of tomato leaves. At first, they are water-immersed chlorotic spots, then gradually expand, and when the humidity is high, the disease spots expand rapidly, which can extend to most of the leaves and even the whole leaves, and can invade into the petiole and stem along the veins to form brown stripes. Finally, a circle of white mold grows on the edge of the plant leaf, which is most obvious on the back of the leaf after rain or in the morning with dew, and can also be produced on the front of the leaf when the humidity is very high. When the weather is dry, the disease spot is dry and brown, there is no white mold on the back of the leaf, it is brittle and easy to crack, and expands slowly. The cortex of the stem forms brown spots of different lengths, and the disease spots also grow sparse white frost molds in humid conditions.

Tomato late blight

The cause of the disease: the occurrence and prevalence of late blight are closely related to climatic conditions, and the speed of development is also closely related to the cultivation conditions of tomato and the disease resistance of the plant itself. The main results are as follows: (1) Climatic conditions: the shortest incubation period of 25 ℃ is only 3-4 days, but too high temperature is not conducive to the epidemic of the disease. Bacteria have strict requirements for relative humidity, more than 75% can occur. (2) cultivation conditions: luxuriant plants, low-lying terrain, poor drainage, excessive humidity in the field are conducive to the occurrence of diseases, barren plants in soil are weak, or partial application of nitrogen fertilizer causes excessive growth, and tomatoes are in the middle and later stages of growth. are conducive to the occurrence of diseases. (3) varieties: tomato varieties with strong disease resistance are not easy to disease, such as Zhongshu No. 4.

Integrated control techniques: (1) selection of disease-resistant varieties such as Baili, Zhongshu No. 4, Zhongshu No. 5, Jiafan 15, Jiafan 17 and so on. (2) choose the land with high dryness and convenient drainage and irrigation to plant reasonably and closely. Rational application of nitrogen fertilizer and increase of potassium fertilizer. Do not flood irrigation, timely drainage after rain. Strengthen ventilation and light transmission, timely ventilation when cultivated in protected areas, to avoid leaf condensation or the emergence of water film, in order to reduce the degree of disease. (3) cultivating disease-free strong seedlings: the pathogen overwinters mainly in soil or diseased remains. Therefore, the seedling soil must strictly select the soil that has not planted Solanaceae crops, and advocate the cultivation of disease-free strong seedlings with nutrition bowls, nutrition bags, hole trays and so on. (4) Clean the countryside: after harvesting tomatoes, cucumbers, peppers, celery and other crops, thoroughly remove diseased plants and fruits, and reduce the source of primary infection. Always check the leaves of the lower part of the tomato plant near the ground. Once the central diseased plant is found, immediately remove the diseased leaf, diseased branch, diseased fruit or the whole diseased plant, bury or burn it deep away from the field, and immediately apply germicidal pesticides and continuous disinfection to prevent the disease from spreading. (5) 75% chlorothalonil wettable powder 700 times liquid, or 25% metalaxyl wettable powder 600 times liquid, or 70% mancozeb wettable powder 500 times liquid can be sprayed once every 5 to 7 days, for 2 times in a row.