The pathogenicity of Fusarium oxysporum f. sp. tritici under different environmental conditions, nutritional conditions, and the influence of host plants and other external ecological factors, but also due to the genetic and variation of the pathogen itself, continue to change, in the long-term evolution, you can gradually form some of the comparison The stable type, physiological or physiological races, have different virulence and different virulence for different cotton varieties. The Plant Protection Institute of the Chinese Academy of Agricultural Sciences conducted international identification of hosts between 1982 and 1984, and identified 17 strains of Fusarium oxysporum in 15 major cotton-producing provinces in China. The results showed that there are 3, 7 and 8 in China. Physiological race. No. 7 races are mainly distributed in major cotton areas such as coastal areas and inland areas; No. 8 races are mainly distributed in the Jianghan cotton area of ​​Hubei Province. Races 7 and 8 were first reported in China.
Fusarium oxysporum f. sp. tritici is a highly specialized pathogen that invades Okra and Cassia in addition to cotton. According to experiments conducted by the Northwest Agricultural College, crops such as sweet potatoes, soybeans, peas, kenaf, sunflowers, tobacco, tomatoes, peppers, and cucumbers can also be infested by Fusarium oxysporum and can spread disease. Only wheat and corn are not infested. Therefore, wheat, corn and cotton dumplings are effective measures for controlling fusarium wilt. According to research by Li Changxing, the cocklebur is also the host of the wilt disease and can exhibit typical symptoms of blight.
The infestation and damage of cotton wilt disease are affected by many factors such as climatic conditions, cotton growth stage, and cultivation and management.
(1)Climatic conditions The soil temperature during the seedling stage of cotton reached 20oC. The infected cotton strain began to show symptoms at 25-30oC and entered the peak of the disease. The condition above 30oC was inhibited. Therefore, the Yellow River valley is the peak of incidence from late May to mid-June. Soil moisture ambassadors lowered the temperature and the incidence was heavier.
(2) Cotton growth stage According to experiments, cotton is the worst onset during budding period.
(3) Cultivation and management Disease-free soil nutrient culture Seedling transplanting helps to reduce seedling disease; early cultivator can increase ground temperature, promote root development, and reduce disease; flood irrigation in cotton fields, increase soil moisture, reduce ground temperature, conducive to disease; The application of nitrogen fertilizer is heavier, and the combination of nitrogen, phosphorus, and potassium is beneficial to reduce the disease; the disease is heavy and the crop rotation is light, but the source of bacteria cannot be eliminated; According to research, many weeds in the cotton field are the host disease of wilt disease, although not Symptoms, but with pathogens, are intermediate mediators of disease transmission, so more cotton fields with weeds are more susceptible to disease; improper application of pre-emergent herbicides, damage to the root system, and serious disease; spray growth of dildoamine and humic acid. Regulators have the effect of reducing disease.
Cotton Verticillium wilt is known as the cancer of cotton. At present, there are no effective control measures and pharmaceuticals in Daejeon. Therefore, we must base ourselves on comprehensive measures for prevention (including the selection of disease-resistant varieties), mobilize all means, and create an environmental condition that is not conducive to the infestation of pathogens and facilitate the robust growth of cotton plants. A large number of examples showed that as long as cotton grows strong from the seedling stage, the disease is light. Therefore, all measures that are conducive to promoting strong trees are also measures to prevent and reduce disease.
At present, there are two major factors in most cotton fields that are extremely detrimental to the prevention of blight: one is not cultivating cotton fields in successive years, and the other is not applying organic fertilizer and cannot balance fertilization. As a result, the cultivars in the cotton fields are too shallow and the bacteria accumulate in the soil at a height of 10 to 15 cm. The roots cannot be pulled down, the soil structure deteriorates, and the organic matter and potassium are seriously deficient. This lays a hidden danger for the occurrence of wilt disease. Once weather conditions are suitable, it will inevitably cause the outbreak of blight.
The climatic conditions in most areas this spring are suitable for the occurrence and development of cotton fusarium wilt, and five types of diseased plants have been found during the seedling stage. However, in the cotton fields of some member leaders, more than 20 cm of autumn ploughing was performed, and nitrogen, phosphorus, and potassium fertilizers and organic fertilizers were applied before the autumn ploughing, which created extremely favorable conditions for strong seedlings, and the cotton seedlings were unearthed. Strong and strong, the incidence is significantly lighter, or basically no incidence. In the cotton field where insecticides are sprayed to prevent diseases, if there are already diseased plants, the concentration of the pesticide should be increased. The diseased seedlings should be irrigated with 200 times of grams of yellow or 50 times of fish protein.
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