Symptoms can develop from the seedling stage to the adult stage. The leaves were damaged, the lesions were brown, water stains, and obvious ring patterns. When wet, the edges are not obvious, and the expansion is extremely fast. There are sparse white molds on the lesions. The lesions cease to expand when dry and the diseased tissue is dry.
The pathogen is Phytopthora parasitica Dast that belongs to the flagellin subphylum. Mycelium is colorless and without a diaphragm. Absorbers are not produced and mycelium penetrates host cells directly to absorb nutrients. Late generation of hyphae and sporangia. Spore cysts, single spores, round. There is a papillary piercing at the top. When the sporangium germinates, multiple elliptic zoospores are produced.
Pathogenic bacteria are mainly borne by oospore with soil in the soil. In the following year, the oospores are splashed on the leaves by rain or irrigation water and the germination tube invades the host. Afterwards, a large number of spore pouches will be generated from the lesions and zoospores will be generated from the sporangia, which will be transmitted through the spread of rain and irrigation water.
1. The suitable temperature for the growth and development of pathogens is 28-30°C, which requires high relative humidity and water droplets. Therefore, high temperatures and high humidity are the conditions for the epidemic.
2. After the film is removed from the plastic shed in summer, continuous rainfall is conducive to the occurrence of diseases.
3, soil viscosity, partial nitrogen fertilizer, management of extensive disease severity.
In the early stages of disease prevention and control methods, spraying protection is required. The agent can be used in 25% metalaxyl 800-1000 times; 58% metalaxyl Mn-Zn in 500 times; 40% EB in 200 times; 64% in anti-mite M8. Powder 400-500 times; or 77% can kill 500 times of wettable particulate powder. Spray once every 7-10 days, spray 2-3 times continuously.
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