In a recent production survey, leaf margin necrosis was found in some of the lettuce fields. Since the disease is rare in the suburbs of Beijing, the farmers were introduced to identify and prevent the disease.
symptom
The disease is a bacterial disease. The pathogen is gram-negative bacteria. It usually begins when the ball is borne, and it mainly damages the leaves. The leaf margin and its vicinity were first affected, initially in water-soaked condition, and after drying it was thin paper-like, presenting brownish to dark brown irregular oily lesions. The margin of the leaf margin is about 1 cm wide. The rest of the leaves are brown spots. Several lesions are contiguous and gradually soften, and some plants quickly dry up or fall off. The general situation is only on the incidence of nodule, its expansion is very slow, affecting development, rarely cause rot. Some of the diseased plants have black or green hard rot tissue at the center of the stem, which can spread along the bottom leaf veins to the roots, causing root rot.
Disease characteristics
Pathogenic bacteria overwinter in seeds, soil, or diseased bodies, invade through wounds, stomata, and lenticels, and spread through mud and air after onset. Low temperature, high humidity, condensation, foggy, and oligos contribute to the onset of disease. In early spring and late autumn, the incidence in the Beijing area is heavy, and the incidence is low and slow at high temperatures in summer. Heavy pods, soil viscosity, acidity, excessive planting density, too much nitrogen fertilizer application, extensive field management, etc.
Comprehensive prevention
Prevention and treatment of the disease should strictly adhere to the principle of “prevention as the mainstay and comprehensive prevention and controlâ€, and pay attention to the control of the source and the application of non-chemical technology. The prevention and control measures are as follows.
1. Seed disinfection. Before sowing, use seed weight 0.3% of the 47% Spring Thunder copper wettable powder or 30% copper citrate copper wettable powder seed dressing.
2. Aseptic soil seedlings. Maize seedlings or disease-free seedlings are used.
3. Qing Yan rotation. With non-Actaceae crop rotation, the former crop was completely cleaned up before planting to remove the sick body, deep-turning the land and exposure for more than 3 days.
4. High mulching film cultivation. Keeping the membrane close to the ground will help reduce the humidity in the field and prevent the bacteria in the soil from contacting the shoots in the ground.
5. Water and fertilizer management. It is forbidden to continue irrigation and flood irrigation, and to prevent mud from splashing on the leaves when watering, which is an important measure to prevent the disease; appropriate application of phosphorus and potassium fertilizers to enhance plant resistance to diseases will help reduce the disease.
6. Farming management. Avoid agricultural operations in rainy weather, reduce the incidence of diseased plants and healthy plants; timely control of pests, reduce plant wounds, reduce the transmission of pathogens; timely prevention and treatment of disease, and remove diseased leaves, diseased plants, brought to the field burned, disease Point application or quicklime.
7. Ecological regulation. The cultivation of facilities should pay attention to the management of temperature and humidity, reduce the humidity in the greenhouse and reduce the amount of dew on leaf surface through measures such as air release and humidity control and irrigation. Temperature control during the day 28 °C -30 °C, 15 °C at night, relative humidity below 70%, conducive to control the spread of the disease.
8. Chemical control. It should be applied in the sporadic onset period of the field. Available pharmaceuticals include 20% copper thiazolyl suspension, 77% copper hydroxide wettable powder, 48% copper acetylphosphonium aluminum wettable powder, 47% wetland copper wettable powder, 30% Humic acid copper WP, 2% kasugamycin, 3% mesitectin wettable powder and so on. Qualified pesticides should be purchased from the regular stores and pesticides should be used according to the pesticide label.
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