What is the reason for curling tomato leaves?

There are many reasons for curling tomato leaves, there are mainly the following: 1, virus. Virus diseases are generally transmitted by aphids, whitefly and other virus-transmitting insects. The susceptible plants are short and the leaves are curly and clustered. In severe cases, there are only veins and no mesophyll in the leaves. Prevention and cure: in addition to selecting virus-resistant varieties and implementing crop rotation, spraying 1000 times of potassium permanganate solution at the initial stage of the disease can cure both virus disease and soft rot, and can also add virus A (K) 100g, chlorfenwei 50g and 25x 30g to 50 kg of clear water to make a mixture spray control, once every 6 days and 3 times in succession. 2. Hormone drug damage. 2when the hormones such as pyrrolidine 4murD and dwarftin are used too much or the concentration is too high, the leaves or growth points of tomato will bend, the new leaves can not expand normally, the leaf edge is twisted, the stem is raised, and the color becomes lighter. Prevention and treatment: it can be controlled by 3000 times solution of natural brassin. 3. Physiological factors. Before and after tomato harvest, the leaves of the first fruit were slightly curled, or the leaves of the whole plant were curled into a tube and became brittle. This is mainly due to high temperature and drought and stomatal closure of tomato leaves. Prevention and treatment: drought-resistant exercise is carried out from plant planting to fruit setting, timely watering and fertilization after fruit setting, and covering the sunshade net, so that the day cover is late, and the cloudy day is not covered. 4. The harm of tea yellow mite. Leaf blade narrowed, stiff and erect, wrinkled or twisted, finally bald. Prevention and treatment: it can be sprayed with 1.8% Aifuding 3000 times or 20% mifenjing 2000 times, once every 6 to 7 days, 2 times in a row. 5. Magnesium deficiency. In the first inflorescence expansion stage, the lower old leaves of the diseased plant lost chlorosis, yellowing appeared between the veins, and then expanded upward to form yellowed variegated leaves, and in heavy cases, the leaves were stiff or rolled up. Prevention and treatment: increase the application of nitrogen, phosphorus and potassium fertilizer or foliar spraying magnesium sulfate 50 times.