How to prevent and cure tomato leaf mold?

The symptoms of tomato leaf mold appear on tomato leaves, stems, flowers and fruits, but what is common is that it occurs on the leaves. Some green spots appear on the back of the leaves at the initial stage, and the irregular mold layer turns gray or black-purple in the later stage. The front of the leaves turn green and yellow in the corresponding parts, and when serious, the leaves often dry and curl. Let's take a look at how to control tomato leaf mildew.

Symptoms of Tomato Leaf mildew

Tomato leaf mildew mainly harms leaves and, in severe cases, also harms stems, flowers and fruits. In the early stage, yellow-green spots appeared on the front of the leaves, the edges were not obvious, the gray-white mildew layer appeared on the back of the leaves, and the mildew layer became light brown to dark brown. When the humidity was high, the mildew layer could also grow on the leaf surface. The disease often occurs first from the lower leaves and gradually spreads upward. When the disease is serious, the mildew layer is covered with the back of the leaves, the leaves are curled, and the leaves of the whole plant are yellowish brown and dry. Similar disease spots can also be produced on the tender stem and fruit stalk, and the floral organ is easy to fall off. Fruit disease, the formation of black round or irregular patches near the pedicel or on the fruit surface, hardened and sunken, not edible.

Pathogenic conditions of Tomato Leaf mildew

Tomato leaf mold likes the environment of high temperature and high humidity. The optimum climatic condition of the disease is 20-25 ℃ and the relative humidity is above 95%. The main peak periods of the disease in Zhejiang and the middle and lower reaches of the Yangtze River are from March to July in spring and from September to November in autumn. The susceptible growth period of tomato is the flowering and fruiting period, and the disease is more serious in the fields with continuous cropping for many years, poor drainage, poor ventilation, closed fields and high air humidity. The disease is serious in early spring when it is cold and rainy, continuous overcast and rainy or Meiyu. The disease is serious in late autumn when the temperature is too high and it is rainy.

How to prevent and cure tomato leaf mold?

1. Rational rotation: tomato and non-Solanaceae crops should be rotated for more than three years in order to reduce the number of bacteria in the soil. At the same time, disease-resistant varieties are selected and seedlings are strictly guarded. Jiafan 15, Jiafan 16, Jiafan 17, Zhongza 7, Shenfen 3 and Jiahong 15 are the varieties with high resistance to leaf mildew in the market.

2. Seed disinfection: the introduced seeds need to be treated and soaked in warm water. Making use of the difference of heat tolerance between seeds and germs, the temperature which can not only kill the germs inside and outside the seeds, but also do not damage the vitality of the seeds was selected for disinfection. The tomato seeds cultivated in greenhouse should be soaked in 55 ℃ warm water for 30 minutes to remove the bacteria inside and outside the seeds, cool them in cold water, soak the seeds with potassium permanganate for 30 minutes, rinse the seeds with clean water for several times, and finally dry and germinate the seeds.

3. High temperature stuffy shed: choose noon time on sunny day, take high temperature treatment of 30: 33 ℃ for about two hours, and then ventilate and cool down in time, which has a better control effect on pathogens. In the early stage of cultivation, we should pay attention to increase the temperature of the greenhouse, strengthen the ventilation and reduce the humidity in the later stage. When the disease develops, you can choose a sunny day at noon, the closed shed to raise the temperature to 36-38 ℃, keep for 2 hours can effectively inhibit the development of the disease.

4. Strengthen management: timely ventilation, proper control of watering, timely ventilation and humidity reduction after watering. The cultivation method of double-ridge plastic film mulching and irrigation under plastic film can not only increase the soil moisture, but also significantly reduce the air humidity in the greenhouse, thus inhibit the occurrence and re-infection of tomato leaf mildew, and plastic film mulching can effectively prevent the spread of bacteria in the soil.