Incidence regularity and control of Sclerotinia sclerotiorum in soybean

Sclerotinia sclerotiorum occurred widely in Heilongjiang Province, and seriously in Raohe County in 2001. The incidence of soybean continuous cropping land was 3%-30%, and that of individual plots of American sunflower crop was 50%.

1 Causes of disease

1.1 Climate conditions in mid and late July continuous low temperature, rainy weather more, temperature between 18-22 degrees Celsius, conducive to the germination of pathogenic fungi ascospores, ascospores become the primary infection source.

1.2 Cultivation conditions one, crop conditions. Sclerotia accumulated in soil year by year in plots planted with sunflower or soybean for many years. Under suitable climatic conditions, sclerotia could form primary infection source and infect host plants such as sunflower, solanaceous crops and soybean.

Second, the choice of varieties. The field investigation of soybean sclerotiorum showed that there were some differences in resistance among different soybean varieties. For example, the incidence of Hefeng 25 was 8.2% after continuous cropping for 2 years, and that of Hefeng 35 was 3.3% after continuous cropping for more than 2 years.

Third, fertilizer application. The soil moisture was too high in the fields with excessive nitrogen fertilizer application, which was beneficial to soybean sclerotiorum occurrence. In the investigation, it was found that urea 4-5kg, diammonium 10-12kg, potassium sulfate 3- 4 kg per mu were applied to the plots with serious disease, and the plant height of soybean was 99-108cm. The incidence rate was about 43.5%.

2 Symptoms of harm

Soybean Sclerotinia sclerotiorum mainly infects soybean stem, upper leaves turn brown and die in the field, and brown spots appear on stem or branches. White flocculent mycelia grow on the spots with high humidity, and gradually form white irregular granular mycelia, then turn gray, until finally form black sclerotia, scattered inside and outside the stem of the diseased plant. At the later stage, the diseased spot tissue was broken, the xylem was exposed, and the whole plant died seriously. When the leaves were injured, they were dark blue, water-stained, rotten, and sometimes flocculent hyphae. It can also infect pods, forming sclerotia inside and outside pods, which can cause seeds in pods to rot, dry and wrinkle, dull, and cause seeds in pods to fail to bear seeds when serious.

3 Preventive measures

3.1 The first agricultural measure is to select seeds. Select good quality, early maturing, disease resistant varieties, and sift seeds to remove sclerotia from interspecies before sowing.

Second, deep down. The plots with serious disease should be deeply turned in autumn, and the sclerotia falling into the field should be buried in the deep layer of soil to make the residues of diseased plants rot and die.

Third, rotation. Rotation with non-host crops or gramineous crops for more than 3 years.

Fourth, drainage and fertilization. The disease can be alleviated by removing accumulated water in time, reducing field humidity and applying less nitrogen fertilizer.

Fifth, shovel. In sclerotia germination period shoveling, can destroy asci disk, reduce disease.

3.2 For chemical control, 800-1200 times solution of 40% Kuanli WP or 2000 times solution of 50% Sukeling WP was sprayed on leaves at the early stage of sclerotium disease, and sprayed once every 7 days. At the peak germination stage of ascocarp, 40% Clerodenm WP could be sprayed at 1000 times. All of the above methods have good control effect.