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The Incidence of Sclerotinia and Its Control Measures
S. sclerotiorum is common in Heilongjiang Province. The incidence was severe in Raohe County in 2001. The incidence rate of soybeans was 3% to 30%, and the incidence rate of individual sunflowers was 50%. The severely diseased plots were even Production. 1. Causes of the disease 1.1 Climatic conditions During the middle and late July, continuous low-temperature and low-temperature sunshine, and more rainy weather, the temperature between 18-22 degrees Celsius, is conducive to the pathogenic fungus ascitic plate germination to form ascospores, becoming the initial infestation source. 1.2 Cultivation conditions First, the mouth conditions. In the plots where the former crop was planted with mallow or the plots with soybeans that were continuously re-plowed for many years, sclerotia accumulate in the soil year after year, and the number of sclerotia grows. When the climatic conditions are suitable, the primary infestation source can be formed and invaded sunflower and tomato. Family crops and host plants such as soybeans. Second, the choice of species. A field survey of S. sclerotiorum found that there are certain differences in the disease resistance of different soybean varieties. For example, the incidence of Hefeng 25 continuous cropping for two years is about 8.2%, and the incidence of Hefeng 35 continuous cropping for more than two years is 3.3%. Third, fertilizer application. Excessive application of nitrogen fertilizer in the plots, the growth of soybeans, field cover, poor ventilation and light transmission conditions, resulting in excessive soil moisture, is conducive to the occurrence of soybean sclerotia. It was found in the survey that the heavy land mass usually applied 4-5kg of urea, 10-12kg of diammonium, 3-4kg of potassium sulfate, and 99-108cm of soybean plant height. The incidence rate was about 43.5%. 2. Injury Symptoms Pathogenic fungi of soybean sclerotia mainly infect the stems of soybeans. The upper leaves of the field plants turn brown and die, and the stems or branches produce brown spots. A white, flocculent mycelium grows on a spot with high humidity, and a white irregular granular mycelium gradually forms, and then turns gray until a black sclerotia is finally formed, which is dispersedly arranged inside and outside the stem of the diseased plant. The later stage lesions shattered to expose the xylem and the entire plant died. When the leaves are damaged, they are dark blue, water-stained, rot, and sometimes flocculent mycelium. Can also infect the soybean meal, in the inside and outside the nucleus, can make the seeds rot, dry wrinkle, dull in the wolfberry, in severe cases can cause pods can not be granulated. 3. Control measures 3.1 Agricultural measures First, select seeds. Select high-quality, early-maturing, and disease-resistant varieties. Before sowing, the seeds are sieved to remove sclerotia mixed in the species. Second, deeper. The severely affected land is subjected to deep fall turning. The sclerotia that has fallen into the field is buried deep in the soil, and the diseased plant body rots and dies. Third, rotation. More than 3 years of rotation with non-host crops or grass crops. Fourth, drainage and fertilization. Timely exclusion of field water, reduce the humidity in the field, the appropriate amount of nitrogen fertilizer can reduce the incidence. Fifth, shovel shovel. In the sclerotia germination period spasm, can destroy the sub-capsule plate, reduce the incidence. 3.2 Chemical control 40% Mosquito WP 800-1200 times or 50% Skoda WP 2000 times, spray on the initial stage of Sclerotinia, spraying once every 7 days. In the germination period of the pathogenic fungus Ascomycote disc, 40% Sclerotium net wettable powder 1000 times solution can be sprayed. The above methods all have better control effect.