Causes and control countermeasures of sclerotia in soybean

1. Symptoms

The browning and death of the upper leaves of the plant in the field was the first to attract attention, and the stem of the diseased plant continued to develop brown disease spots, white cotton flocculent mycelium and white particles, and then turned black to become sclerotia. In the stem of the longitudinal dissection plant, there were black cylindrical sclerotia arranged in turn. The diseased plant is gray-white after death, the hollow cortex of the stem is often rotten into hemp silk, and the sclerotia outside the diseased plant is easy to fall off. The disease spot on the pod is brown, quickly withered and unable to bear fruit, and finally the whole pod is pale. Although the mildly diseased pod can be granulated, the diseased grain is rotten or dried and wrinkled.

2. The cause of disease

The main results are as follows: (1) the previous winter is warm winter, less snow, it is suitable for sclerotia to overwinter in the soil, the more serious the occurrence of Sclerotinia sclerotiorum, the more overcast weather and high soil water content after June, which is also an important reason for the serious occurrence of Sclerotinia sclerotiorum.

(2) the disease of soybean continuous cropping land is serious. According to the field investigation, the incidence of continuous cropping land is more than 30%. In addition, the disease of sunflower stubble and rape stubble is also serious, which is related to a large number of sclerotia left in the field.

(3) excessive application of nitrogen fertilizer will lead to serious disease. With the application of too much nitrogen fertilizer, the soybean grows luxuriantly, the stem is weak, and the disease is serious in the lodging area.

(4) the disease is serious in the plots without ploughing. The seedling nucleus fell into the field and germinated to form ascomycetes and ascospores under suitable conditions in the second year, which became the primary infection source in the field. The disease is serious in the land with less shoveling times, and the land sown in the original ridge is heavier than the sown land.

3. Prevention and control countermeasures

(1) selected seeds: remove sclerotia mixed between seeds before sowing.

(2) Deep ploughing: after the soybean harvest, the sclerotia that fell into the field was buried in the deep soil. When the soil was covered more than 10 cm, the sclerotia could not form an ascomycete disk, inhibit sclerotia germination and reduce the source of primary infection.

(3) crop rotation: rotation with Gramineae crops and other non-host plants for more than 3 years.

(4) strengthen the field management: timely eliminate the stagnant water in the field and reduce the humidity in the field. Do not apply more nitrogen fertilizer, can reduce the disease, shovel in the sclerotia germination period, can destroy the ascomycete disk, reduce the disease.

(5) Field control: in the initial stage of the disease, the drug was sprayed every 10 days, twice in a row. The commonly used agents and their concentrations are as follows: 50% sucryl wettable powder 1000 Mel 1500 times liquid, 50 ml 75 litres per 667 square meters; 50% carbendazim wettable powder 5000 times liquid, 50 ml 75 litres per 667 square meters; 50% nonglide wettable powder 5000 times liquid, 50 murals 75 litres per 667 square meters; 40% sclerotia net wettable powder 1000 colors 1500 times liquid, per 66750 square meters 75 litres.