1, the symptoms of Sphaerotheca nucleatum
The disease occurred in the stem base of the oiled wheat dish. The lesion started as a brownish water stain and gradually developed to decay at the base of the entire stem. When the humidity is high, cotton flocculent white mycelium grows on the surface of the diseased area, and then sclerotia are formed. The size is 4 mm in length and 2 mm in width. The sclerotia were white at first, and gradually became rat fecal black particles. The yellow leaves of the infected plants withered and eventually caused the whole plant to die.
2. Identification of Sclerotinia sclerotiorum pathogens
The pathogen is Sclerotinias clerotiorum (Lib.) de Bary, belonging to the ascopoea of ​​the fungus community. The sclerotium of the pathogen is white at first and the back surface is blackened. It is formed by the combination of pseudo-thin-wall tissue and filamentary tissue, and is generally (1.3-14) mm (1.2-5.5) mm. The sclerotia germinate under suitable conditions to produce light brown ascariform discs. They appear as milky white buds and then expand into cups or discs. They become brown or dark brown after ripening. Many ascospores and lateral filaments are produced in the disc. Ascospores are smoke-like bombs. The ascus is colorless, stick-like, with 8 endogenous ascospores. Ascospores are elliptical, unit cells, colorless, and (10-15) μm (5-10) μm in size.
3, the law of the incidence of Sclerotinia sclerotiorum
The sclerotia are mainly left over in the soil as the disease remains in the soil, and they can also be mixed in the seeds for winter and spread with the seeds over long distances. The germs in wet soils survived for about one year, dry soils survived for more than three years, and water rotted after one month. Sclerotia do not sleep, in the case of sufficient water absorption, 5-20 °C can germinate, 15 °C optimum. After the sclerotia germinates, the ascitium plate is generated, thereby forming ascospores and ascospores. After the ascospore matures, it spreads by air flow and irrigation. At the time of initial infection, ascospores germinate to produce germ tubes that invade from senescent or locally necrotic tissue. When the fungus gets stronger infectivity, it can directly infect the stems and leaves of nearby healthy plants through contact with mycelium. In the field, spread from the central disease spread to all directions. In addition, germs can be transmitted to vegetables through susceptible weeds such as grey ashes.
4. Factors affecting the onset of Sclerotinia sclerotiorum
The temperature is 20°C, and the relative humidity is higher than 85%. Humidity is less than 70% and the disease is significantly reduced. In addition, excessive colonization density, poor ventilation and light transmission conditions, partial application of nitrogen fertilizer, poor drainage of low-lying land, or continuous cropping and other diseases are prone to occur. The incidence in the protected area is heavier.
5, agricultural control of Sphaerotheca sclerotiorum
5.1 selection of disease-resistant varieties for seed disinfection
Use resistant varieties. Such as red lettuce, hanging red, red round and other reddish varieties more resistant. In addition, the seeds are sterilized. The sclerotia mixed in the seeds can be removed by soaking in 8% saline, and the treated seeds must be washed with clean water and then sown. It is also possible to use 50% thiram WP or 40% bacteriostatic WP or 50% skeletal wettable powder dressing.
5.2 Choosing the right plot
Select high-level terrain, convenient drainage and irrigation, deep soil, in recent years did not plant oil and wheat, organic-rich, loose sandy loam, pH value required in the 7-8 plots. With tomato, gourd and other vegetables in the rotation, the effect of rotation is better, which can effectively reduce the occurrence of diseases.
5.3 Debris removal in field and soil disinfection
Before sowing or transplanting, or after harvesting, weeds are removed from the field and surrounding areas, and burned or irrigated; the soil is extirpated by deep plowing, which promotes decomposition of diseased bodies and reduces pathogens and worms. Field diseased plants were removed in time to reduce field bacteria.
In the recurrence area of ​​Sphaeroprostemonium sclerotiorum, the spring period after the harvest of spring amaranth, 100kg of lime per 667m2, 500kg of crushed rice straw, deep 25-30cm deep, high ridge irrigation, mulching with large water cover, treatment for about 30 days During the period, the ditch is always filled with water, which can rot the sclerotia in the soil.
5.4 Proper colonization
To cultivate age-appropriate seedlings, 6-8 true-leaf seedlings are suitable. With soil colonization, the transplanting density should not be too high, the quality of the cover film should be improved, and the black plastic film cover should be used to block the unearthed ascular disc from under the membrane so that it can not obtain sufficient scattered light and most of them cannot complete the development process. Significantly reduce the rate of initial infestation. The timely removal of diseased leaves or the removal of diseased plants is deeply buried, and combined with chemical control, but in the high temperature period, attention should be paid to watering and cooling, or delaying the period of planting to avoid high temperature damage.
5.5 Reasonable fertilization
More cooked organic fertilizer, rational application of nitrogen fertilizer, increased application of phosphorus and potassium fertilizer, promote healthy growth of oil and wheat dishes, improve plant resistance. Every 667m2 of basal fertilizer will be applied with 3000-4000kg organic fertilizer, 7.5-10kg phosphate fertilizer and 10-15kg potassium fertilizer. After the plants were opened, top dressing was started. Also, 0.2-0.5% of compound fertilizer could be sprayed or sprayed with Opal Organic Active Liquid Fertilizer 600-800 times to increase resistance to disease.
5.6 Strengthen field management, timely irrigation and drainage
Timely early sowing, timely cultivating soil, nurturing strong seedlings. Properly dense planting, increase the ventilation of the field. Timely watering and ventilating, proper control of watering before and after the onset of growth, choose sunny watering in the morning, and release air in a timely manner, rainy days, and rainy days, the night minimum temperature higher than 8 °C overnight release dampness. In case of continuous rainfall, spray prevention after rain.
5.7 high temperature stuffy shed
Use Sclerotinia sclerotiorum conidia to infiltrate slowly or in dormant state above 33°C, close the ventilation vent of greenhouse in noon at noon, make the greenhouse temperature increase to 35-38°C and keep it in high temperature for 2-3 hours. , And then let the wind cool and dehumidify, 2-3 times a week.
6. Chemical control of Sphaerotheca
At the beginning of the disease, spray 50% Sulferil wettable powder 1000-1500 times, or 25% polymyxin wettable powder 1000-1500 times, or 50% nongrill wettable powder 600- 800 times liquid, or 70% thiophanate-methyl WP, 700 times, or 50% acetaminophen WP 1000-1500 times, or 20% CK, 1,000 times, separated by 7- Spray 10 times a day, spray 3-4 times continuously. It has also been reported that spraying 12.50% diniconazole 2500 times per acre 80 kg liquid (large doses throughout the stems, leaves and the ground), control of Sphaerotheca arinae disease, and can promote growth.
The dust or smog method can be used in the protected area, with 6.5% vanillin dust and 5% cream dust (1:1 mixture), 2.5-3kg per mu; the smoke method can use a smoked or smoked spirit , A dose of 250g per mu, smoked once every 7 days, even smoked 3-4 times.
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