ã€symptom】 The main damage stems. At the beginning of the rhizomes, oil-like dark green strips appeared, quickly expanded into dark brown irregular shapes. When severe, the stems and leaves became dark. The plants quickly collapsed, and the roots and necks sag, resulting in plant lodging and death. Under conditions of high humidity and long duration, the disease minister sparsely isolates the white mold, the cysts and sporangia of the pathogen. ã€Pathogenic morphological characteristics】 Fast growth on CMA, OMA, V4A medium, spore production, slow growth on PDA medium, no production of oospores. Colonies white, cotton flocculent; mycelium colored, without diaphragm, branching; sporangia sessile colored, without diaphragm, five branches, width 4-5um, a sporangium on it; sporangia oval to oval , Topped, short-stemmed, mature and deciduous, apically distinct papillae, size 32-54x19-30 (um), more than 50 zoospores after germination; some sporangia can also be germinated directly 1 . Sporangia 2-3. Sporangia and zoospore 4-6. Invasive germ tube; ovipositor spherical, colorless to pale yellow, thin membrane, size 28 egg device, lateral male and oospore 7. Occlusion device and perinatal male - 32um. The temperature limit for the growth of germs is 10-32°C; the growth of mycelium is fastest at 25°C. And the oospore adapts to pH3.5-11.5, the optimum pH is pH6, pH3, pHl2 mycelium cannot grow. The bacteria were lethal at 50°C for 20 minutes or 45°C for 40 minutes. Transmission routes and conditions The pathogenic bacteria in the seeds or in the form of mycelium and oospore in the soil overwintering in the soil, the mycelium and sporangia can not winter in the soil, but the oospore can survive in the soil for 4 years, the oospore is the The main source of bacteria for the initial infection, through wind and rain and irrigation water, zoospores can directly invade the roots of impatiens, is the main organ reinfection. The sporangium germinates and releases 10-36 zoospore, and the sporangia can also germinate and grow buds and appressorium directly. The invading filaments invade the leaf tissue through the leaf stomata and act as conidia. The water droplets are needed to complete the above process. . Various lesions on stems and leaves can make the disease worse. Infected seedlings cause lodging, adult plants, heavy rain, high humidity or heavy soil, low-lying land, and severe disease. ã€Popular Trends】 Temperature 20-25 °C, humidity lasts 15 hours, 50% infected. The temperature and humidity duration and their interactions have a great influence on the infection effect of the bacteria. The longer the humidity duration, the more conducive the pathogen infection. Germ development temperature 27 °C ~ 31 °C, the highest 36 °C, the lowest 10 °C. Temperature below 20 °C, higher than 25 °C, need to increase the duration of condensation can quickly infect. Entering the rainy season or heavy rainstorms are prone to disease. [control methods] 1. Remove diseased leaves; increase phosphorus, potassium fertilizers and so on. Reduce the initial infestation source. Do a good job in garden sanitation, use every new year's soil, and plow the land many times in the summer. After sufficient sun exposure, the viability of the fungus will be reduced. Sunlight can make the dormant oospore germinate, thus losing the ability to infect; autumn completely removes the sick Can reduce the incidence. 2. Spray 75% chlorothalonil wettable powder 500 to 600 times, or 40% triethylphosphonate (ethylaluminophosphate) 200 times wettable powder, 70% phenylphosphine manganese zinc wettable powder 500 times Liquid, 58% Metalaxyl Manganese 400~500x, 72.2% Prokary Water 700~800x, 64% Anti-Dry Mist Wettable 500x, or 72% Kelu/Cryo-Cyanide or Cream Urea Manganese Zinc wettable powder 600 times, 60% extinction (zinc manganese fluoride) Wettable powder 800 times, 69% Ankang zinc wettable powder 800 times. 3. Prevent rain splashing and spreading, and play an important role in reducing the incidence of aboveground diseases. L-size Onions,Big Size Onions,L-size Red Onions,Big Size White Onions Yirun Agricultural Cooperative , https://www.yiruncn.com