Pear scab can infect all young green tissues of pear trees: inflorescences, leaves, petioles, new shoots, bud scales and fruits, among which leaves and fruits are the main ones. The most typical symptom is the obvious black mold layer in the affected area, so it is also called black mold. The damage of leaves mostly occurs on the back of leaves, with black mildew spots, and the front of leaves is polygonal or round chlorosis spots. In severe cases, the front and back of the leaves are covered with a black mold layer, which causes the leaves to dry up and fall off. Petiole injury produces round or long mildew spots and leaves fall off. In the later stage, the cortical cracks are rough scabs except for strip mildew spots. When the fruit is damaged, it is pale yellow spots at first, and gradually expands to grow black mold. Later, the diseased part was corked, stopped growing, and the deformation was easy to fall off. ? Cucumber powdery mildew mainly harms cucumber leaves. When it happens, the leaves form white and nearly round powder spots, and the spores of the pathogen are mainly spread by airflow and rain. The higher the humidity, the more serious the illness will be. We should pay attention to cultivation techniques and plant protection methods in prevention, and pay attention to the combination of comprehensive plant protection measures and pesticide application in treatment. Cucumber powdery mildew, commonly known as "white disease", is most seriously affected by leaves, followed by petioles and stems, and generally does not harm fruits. At the beginning of the disease, small white powder spots are produced on the front or back of the leaves, which gradually expand into a large area of white powder area with inconspicuous edges, covering the leaves, as if a layer of white powder was sprinkled.
Wipe off the white powder and you can see that the leaves are green, yellow and crisp. When the disease is serious, the leaves are covered with white powder and turn gray until the whole leaves die. After powdery mildew infects petioles and tender stems, the symptoms are similar to those on leaves, but the lesions are smaller and there is less powder. Yellow spots began to appear on the leaves, and then expanded into round or oval lesions with a white powdery mildew layer on the surface. Generally, there are more lower blades than upper blades, and there are more behind blades than in front. The mildew spots are scattered separately in the early stage, and then combined into a large mildew spot, which can even cover the whole leaf, seriously affecting photosynthesis, interfering with normal metabolism, causing premature aging and yield loss. Mangzinone is a mixed bactericide composed of triadimefon and mancozeb. The products are 33% and 40% wettable powder. Trade names include Fruitful Fruits, Bald Rust Garden, Fourgaut, Black Star Well, Fast Green and so on. The manufacturers are pesticide plant in Weixian County, Hebei Province, Jingbo Agrochemical Co., Ltd., Shouguang pesticide plant, Shaanxi Yangling Bodisen Biotechnology Development Co., Ltd., Tianjin Kang Jie Chemical Co., Ltd. and Chongqing Jiazhi Biochemical Co., Ltd. to control pear scab, using 33% wettable powder 800~ 1200 times. To control cucumber powdery mildew, use 40% wettable powder100 ~150g per mu and spray water regularly.