The blight of impatiens

[symptoms]

It mainly harms the stem. The first root and stem showed oil-stained dark green strip patches, which became black-brown and irregular after rapid expansion, and in severe cases, the stems and leaves all blackened, and the plant was quickly folded and the root neck sunken, resulting in plant lodging and death. Under the condition of humidity saturation and long duration, the disease developed sparse white mold, that is, the sporangium and sporangium of the pathogen.

[morphological characteristics of pathogens]

It grows fast and produces more spores on CMA, OMA and V4A media, but grows slowly on PDA medium and does not produce oospores. The colony is white and cotton-like; the hyphae are five-colored, without septum and branched; the sporangium is five-colored, without septum, five branches, wide 4-5um, and a sporangium is attached to it; the sporangium is oval to oval, terminal, with short stalks, and falls off after maturity, with obvious papillae at the tip, 32-54x19~30 (um) in size, and produces more than 50 zoospores after germination. Some sporangia can also germinate directly and produce 1. Sporangia 2-3. Sporangia and zoospores 4-6. Invading germ tubes; oviparous apparatus spherical, colorless to light yellow, thin membrane, 28 egg organ, lateral male organ and oospore 7. Egg organ and perinatal male organ-32um. The growth temperature limit of the pathogen was 10 ℃ 32 ℃, and the mycelium grew fastest at 25 ℃. And oospores adapt to pH3.5-11.5, the most suitable is that pH6,pH3 and pHl2 hyphae can not grow. The strain was killed by 50 ℃ in 20 minutes or 45 ℃ in 40 minutes.

[route of transmission and conditions of onset]

The pathogen overwinters on seeds or in the form of mycelia and oospores in the soil. The hyphae and sporangia can not survive in the soil, but the oospores can survive in the soil for 4 years. Oospores are the main source of primary infection. Zoospores can directly invade the roots of Impatiens balsamina by wind, rain and irrigation water. Sporangia germinate and release 36 zoospores. Sporangia can also germinate directly and grow germ tube and appressorium. The invading filaments invade leaf tissue from leaf stomata and play the role of conidia. Water droplets are needed to complete the above process. Various scars on stems and leaves can aggravate the disease. Disease bacteria infect seedlings and cause lodging. At the adult stage, there are more Rain Water, high humidity or heavy soil viscosity, low-lying terrain and serious disease in continuous cropping land.

[popular trends]

The temperature is 20 Mel 25 ℃, the humidity lasts for 15 hours, and 50% of the patients are infected. The duration of temperature and humidity and their interaction have a great influence on the effect of bacterial infection, and the longer the duration of humidity, the more favorable for bacterial infection. The optimum temperature for the development of the pathogen was 27 ℃ ~ 31 ℃, the highest was 36 ℃ and the lowest was 10 ℃. If the temperature is lower than 20 ℃ and higher than 25 ℃, it is necessary to increase the duration of condensation in order to infect rapidly. It is easy to get sick after entering the rainy season or after heavy rain.

[prevention and control methods]

1. Remove diseased leaves and increase the application of phosphorus and potassium fertilizer. Reduce the source of primary infection. To do a good job in garden sanitation, using soil every other year, and ploughing the land many times in hot summer, the viability of the bacteria was reduced after full sun exposure, and the dormant oospores germinated, resulting in the loss of infection ability, and the incidence of disease could be reduced by thoroughly removing the residual body in autumn.

two。 Spraying 75% chlorothalonil wettable powder 500 times 600 times at the initial stage of the disease Or 40% aluminum triethylphosphonate (ethyl aluminum phosphate) wettable powder 200 times, 70% ethyl phosphine manganese zinc wettable powder 500 times, 58% metalaxyl manganese zinc 400 times 500 times, 72.2% pric water 700 times 800 times, 64% detoxification alum wettable powder 500 times or 72% gram cyanide or frost urea manganese zinc wettable powder 600 times, 60% chlorhexane (fluoromanganese zinc) 800 times, 69% Anke manganese zinc wettable powder 800 times liquid.

3. Preventing Rain Water from sputtering and spreading plays an important role in reducing the incidence of aboveground disease.