Control methods of Sclerotinia sclerotiorum in Chrysanthemum

First, the symptoms of damage: waterlogged disease spots appeared in the middle and lower part of the stem at first, and then turned gray; under humid conditions, the disease part was soft rot, superficial white mildew layer, and in the later stage, the cortex of the diseased stem was moldy and fissured, and there were mouse dung-like black sclerotia in the endophy. sometimes sclerotia are also produced on the stem surface. 2. Morphological characteristics of pathogens: the pathogen is the sclerotia produced by Sclerotiniasclerotiorum (Lib.) deBary, which is oval, irregular, initially white, and then the outer becomes black, the size of 2~5Xl~3 (mm), on PDA, the flora is white, felted, the mycelium is spreading, rough, and grows rapidly. The hyphae are pentachromatic, branched, and produce conidiophores. Some small bottle peduncles are irregularly clustered at the top of the conidiophores or at the top of their branches, and the tiny conidia with dense pentachromatic unicellular cells are only 1.5 × 1 / 2 microns in size. A week later, a large black irregular sclerotia was gradually formed in the outer layer after initial white. Third, the characteristics of the disease: overwintering with sclerotia in the soil, on the diseased remains or mixed in compost. The sclerotia of overwintering sclerotia germinated under suitable conditions to produce ascomycetes. After the ascomycetes matured, the spores were emitted and spread with the wind to infect the surrounding plants in case of the change of air humidity. In addition, the sclerotia sometimes directly produces hyphae, the hyphae on the diseased plants have strong infectivity, the hyphae develop rapidly, and the pathogenic parts rot. Sclerotia are produced when nutrients are consumed to a certain extent, and sclerotia germinate without dormancy. The disease occurs under cool and humid conditions, and the optimum temperature is 5-20 ℃ and 15 ℃. Ascospores 0 Mel 35 ℃ could germinate, and 5 Mel 10 ℃ was the most favorable. The mycelium could grow at 0-30 ℃, and 20 ℃ was the most suitable. The temperature of sclerotia formation was consistent with the temperature required for mycelium growth, and 50 ℃ of sclerotia was killed in 5 minutes. Bacteria have strict requirements for humidity. In moist soil, sclerotia only survive for 1 year; long-term stagnant water in soil will die within 1 month. It can survive for more than 3 years in dry soil, but it is not easy to germinate. Sclerotia germination requires high humidity and cool conditions. The development of ascomycetes after germination requires sufficient water for 10 consecutive days, relative humidity 70%, ascospores can survive for 21 days; relative humidity 100% only survived for 5 days. It occurred in Guangdong from October to December, and the damage was serious. 4. prevention and control methods: at the initial stage of the disease, 40% polysulfide suspension 600-700 times or 70% thiophanate methyl wettable powder 500-600 times, 50% mixed thiophanate 600 times, 80% carbendazim 600-700 times, 35% sclerotia light suspension 600-800 times, once every 7-10 days, 2-3 times in a row.