Sunflower sclerotinia, also known as white rot, is commonly known as rotten disease. This disease occurs in different degrees in the main sunflower producing areas every year. The incidence rate is generally around 50%, and in severe cases it can reach more than 80%. It has a great influence on the yield and quality of sunflower. Timely pesticide control is critical.
I. Symptoms of the disease Sunflower sclerotinia can occur in the whole growth period of sunflower. There are two types of disease symptoms.
1. Standing dry type. It can occur from the beginning of the seedling to the formation of the disk. The seedling stage is mainly in the base of the stem, forming a water-soaked lesion around the stem. When wet, the white flocculent hyphae grows. After drying, the diseased part shrinks and the black sclerotium forms in the stem, and the plant is dead and dead. The adult stage is also dominated by the base of the stem, showing a light brown moist lesion, and then gradually expanding to the stem of the whole plant. In the later stage, the lesion is dry and grayish white, the edge is brown, and the epidermis is ruptured due to stem conduction. The organization suffered damage and affected the transportation of nutrients. The leaves began to turn yellow from the bottom to the top, withered and detached, and finally the whole plant died.
2. Bad disk type. This condition is mainly the heaviest after the flowering period. When the disk is damaged, a water-soaked lesion appears on the back of the disk, and the receptacle becomes brown and softens. In the rainy weather, the lesions begin to expand rapidly, and can penetrate the flower disk, from the back of the black heart to the front, and grow a white hyphae, causing the disk to rot, so that the grain can not mature, causing the seed kernel to rot or seed rot Fall off.
Second, the cause of the disease is mainly caused by germination of sclerotia. According to the pesticide network , the bacteria overwinter in the soil, diseased tissues and seeds in the sclerotial state, and generally live in the soil for 2 to 5 years. There are two ways to infect it: First, a hyphae is produced after germination of the sclerotium. When it comes into contact with the "host", it directly invades. The seedling stage and the adult stage are the infection modes; the second is the sclerotia. The ascospore disc can be produced, and the ascospores are transmitted to the "host" through wind and rain or insects, and the sunflower rotten disc is caused by the infection of the ascospores. Generally, when the temperature is 20 ° C and the relative humidity is 80%, it is most suitable for the germination of sclerotia, which is also the most serious period of flower disk incidence. Especially in the rainy years, the incidence rate is the highest on some plots with low drainage, poor ventilation and poor ventilation, and repeated years of heavy or pleasing. The incidence rate is also highest when it is rainy and cold from July to August.
Third, prevention and treatment measures 1. Pull out the diseased plants. When you find this disease, you should immediately remove it to prevent it from spreading.
2. Chemical control. (1) Spraying the lower part of the plant and the back of the disk one or two times before the sunflower is budded or in the flowering stage with 40% of the stalks of 800% to 1000 times; (2) using 50% thiophanate wettability 1000 times of powder, sprayed once or twice before the flowering of the sunflower or during the flowering period; (3) spraying with 500% to 1000 times of the 50% fungicide, the speed of the seedling or flowering period, the control effect can be Up to 80% or more; (4) According to the law of the occurrence of sunflower sclerotinia, when the temperature reaches 18 °C ~ 20 °C, the water content of the surface soil of 0 cm ~ 5 cm is above 11%, when the ascospore begins to be unearthed, the ground is sprayed The best period, 70% to 45 kg of nitrochlorobenzene per hectare, plus 150 kg to 225 kg of moist fine soil, mixed evenly and sprinkled in the sunflower field, can inhibit the germination and killing of sclerotia The germination rate of the young sprout tube that has just sprouted is generally 91.3%, and the control effect is over 78.5%.
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