What are the latest control methods for tomato leaf mold?
Tomato leaf mold shows symptoms on the leaves, stems, flowers and fruits of tomatoes, but it most commonly occurs on the leaves. In the early stage, some chlorotic spots appear on the underside of the leaves, and later they turn into gray or dark purple irregular mold layers, while the upper surface of the leaf turns chlorotic and yellow at the corresponding parts. In severe cases, the leaves often dry up and curl. Let us take a look below at how to control tomato leaf mold!
Damage symptoms of tomato leaf mold
Tomato leaf mold mainly damages the leaves, and in severe cases also damages the stems, flowers and fruits. When the leaves are affected, yellow-green spots with inconspicuous edges first appear on the upper surface of the leaves, and a grayish-white mold layer appears on the underside of the leaves, after which the mold layer turns light brown to dark brown. When humidity is high, mold can also grow on the lesions on the leaf surface. The disease often starts on the lower leaves first and gradually spreads upward. When the disease is severe, the mold layer covers the entire leaf underside, the leaves curl, and the whole plant's leaves turn yellow-brown and dry up. Similar lesions can also appear on young stems and fruit stalks, and affected flowers tend to drop off. When the fruit is affected, black round or irregular patches form near the fruit stalk or on the fruit surface, becoming hard and sunken, and the fruit is unfit to eat.
Conditions for the onset of tomato leaf mold
The tomato leaf mold pathogen prefers high temperature and high humidity environments. The most suitable climatic conditions for the disease are a temperature of 20-25°C and a relative humidity above 95%. In Zhejiang and the middle and lower reaches of the Yangtze River, the main peak periods of the disease are spring from March to July and autumn from September to November. The susceptible growth period of tomatoes is the flowering and fruiting stage. Fields with many years of continuous cropping, poor drainage, poor ventilation, overly dense canopies and high air humidity are more severely affected. In years with low temperatures and frequent rain in early spring, continuous rainy days or a rainy plum rain season, the disease is severe. In autumn, in years with relatively high temperatures in late autumn and frequent rain, the disease is severe.
How to control tomato leaf mold?
1. Reasonable crop rotation: Tomatoes are best rotated with non-solanaceous crops for more than three years to reduce the base level of pathogens in the soil. At the same time, choose disease-resistant varieties and strictly control the seedling stage. Among the varieties promoted on the market, those with high resistance to leaf mold include Jiafen 15, Jiafen 16, Jiafen 17, Zhongza No. 7, Shenfen No. 3, Jiahong 15, etc., which can be selected for planting according to local conditions.
2. Seed disinfection: Introduced seeds need seed treatment and should be soaked in warm water. Taking advantage of the difference in heat tolerance between seeds and pathogens, choose a temperature that can kill the pathogens inside and outside the seeds without damaging the vitality of the seeds for disinfection. For tomato seeds for greenhouse cultivation, it is advisable to soak the seeds in 55°C warm water for 30 minutes to remove pathogens inside and outside the seeds. After taking them out, cool them in cold water, soak them in potassium permanganate for 30 minutes, then take out the seeds and rinse them several times with clean water, and finally dry them in the sun, sprout them and sow.
3. High-temperature greenhouse sealing: Choose around noon on a sunny day and carry out a high-temperature treatment of 30-33°C for about two hours, then ventilate and cool in time, which has a good controlling effect on the pathogens. In the early cultivation stage, pay attention to raising the greenhouse temperature, and in the later stage strengthen ventilation to reduce humidity. When the disease develops, choose noon on a sunny day, close the greenhouse tightly to raise the temperature to 36-38°C, and keep it for 2 hours, which can effectively inhibit the development of the disease.
4. Strengthen management: Ventilate in time, control watering appropriately, and ventilate promptly after watering to reduce humidity. Using double-ridge plastic mulching and under-film irrigation can not only increase soil moisture, but also significantly reduce the air humidity in the greenhouse, thereby inhibiting the occurrence and reinfection of tomato leaf mold, and plastic film mulching can effectively prevent the spread of pathogens in the soil.