Orchid gray mold is also known as orchid flower rot. In southern and northern China, flower gardens occur from time to time, with the exception of orchids that are harmful to Orchidaceae plants, they also endanger flowering plants such as Phalaenopsis, Catalans, Dendrobium, Millettia, and Helianthus. Among them, horticultural treasures such as Phalaenopsis, Cymbidium, and Muran are seriously affected. 1. Symptoms Phalaenopsis cinerea mainly damage flower organs, sepals, petals, pedicels, and sometimes also damage leaves and stems. In the early stage of disease, petal and calyx are infected, and after 24 hours, small translucent water stain spots can be produced, and then the lesion turns brown, and sometimes there are white or pale pink circles around the lesion. The number of lesions on each flower varies, but when the flowers begin to fade, the lesions increase rapidly and the petals turn dark brown and rot. When the humidity is high, fluffy, rat grey growths, that is, conidial stems and conidia of pathogenic bacteria grow from decaying flowers. Pedicel and stems became infected, and water-stained dots appeared early in the experiment, gradually expanding into circles and oblong lesions, dark brown, and slightly sinking. When the lesions expand to about one week, the flowers die. When the leaves are damaged, the tips of the leaves scorch. The disease occurs more than 2 to 3 peaks in early spring and autumn and winter each year. When it is serious, it is full of lesions and it is full of gray molds. This is a catastrophic disaster for orchids that are "appreciating flowers like flowers" or "special flowers." At high temperatures, the disease is limited to older, dying flowers. When flowers begin to age or weaken, a variety of orchids can infect the disease. 2. The pathogen was identified as the pathogen of the disease Sclero-tinia fuckeliana (de Bary) Fuck, which belongs to Ascomycete fungus. The asexual state is Botrytis cinerea Pers. exFf. Called Botrytis cinerea, a species of the genus Alternaria. When the conditions are poor, sometimes the disease minister produces a sheet-like sclerotia. The surface of the sclerotia substrate is of a size ranging from 3 to 4.5 mml. 8 to 3 mm, and the small diameter is only 11 mm. In the Chest's medium, the sclerotia are mostly buried half, size 2.5 ~ 15mm, round to oblong. The sporangial stage is common, the silk sperm is white, the groups are grayish, the spores are spherical, and the size is 3 to 4 microns. The anamorphous state of the colony was grayish white and browned afterwards. The conidial stems are scattered or clustered in the colonies, light brown to brown, with a septum, 280 to 350 micron in size l2 to 24 micron, 1-2 branches at the top, slightly inflated, and some stick-like, dense and small Stem, a large number of conidia. Conidia widely oval, more, unit cells, nearly colorless, size 6 to 8 microns 5 to 12 microns. Scanning electron microscope, the spore surface is smooth. In ornamental plants, the bacteria in addition to invading orchids can also infect bulbous sea bream, cyclamen, calendula, duckbill, stick oyster, gloxinia, canna, cleome, wenshulan, coral flower , Dahlia, Rhubarb, yarrow, hibiscus, gladiolus, petunia, hibiscus, chrysanthemum, marigold, poinsettia, camellia, jasmine, rose, cherry blossom, azalea, a bunch of red, calla lily and Other flowers. 3. Transmission routes and pathogenic conditions The bacterium sclerotia wintered in the soil of 5-12cm. When the temperature in Hunchun is 7～8°C and the relative humidity is more than 88%, a large amount of mycelium and conidia are produced on the sclerotia. The conidia are transmitted by air flow, water droplets or dew and gardening operations. The disease's expansion is gradual. After the seedlings are invaded, the bacteria can colonize. It often spreads with the growth of plants. Before flowering buds, it harms the stems or leaves or lurks. After flowering, as long as the disease conditions are appropriate, the flowers will quickly become infected. The occurrence of gray mold is greatly affected by the conditions of the disease. Sclerotia can germinate at 5-30°C, germinate only at 1 day at 21°C, and germinate at 5°C for 5 days. The starting temperature of mycelial development is 2°C, the highest is 31°C, and the optimum temperature is 20～23°C. The optimal germination temperature of spores was 18-24°C, which germinated at 21°C for 24h. The germination rate was 72.6%. After germination at 35°C for 24h, only spores germinated, and 37°C could not germinate. The bacteria usually have stricter humidity requirements than those with less than 84% of RH spores, and germination is above 88%. The highest spore germination rate is between 92% and 95%. RH80% only produced conidia after 15d, RHl00% only required 3d to produce spores. In addition, high humidity is beneficial to the invasion, expansion, and prevalence of pathogens, and the incubation period can also be shortened. The bacteria infestation needs certain nutrition, such as the fallen petals or the stigmas that have been powdered, and the wounded stems and leaves are all susceptible to infection by Botrytis. After the bacteria invade, they become rotted and when they form a colony, they infect the vigorous flower or stem. Prevalence of this disease in nurseries or sheds often requires the accumulation of bacteria. The site of infestation of Botrytis cinerea is mainly the calyx, petals and stigma. The source of the disease is the soon-to-be-fallen flowers. Therefore, the weather conditions of the orchid flowering period have a greater impact on this disease. Here, the temperature is 7 to 18°C ​​and RH is higher than 88%. The relative humidity in plastic sheds, greenhouses, and living rooms can often meet the morbidity requirements, and indoor air temperature is the limiting factor for the epidemic. When the number of days below 18°C ​​occurs, gray mold begins to occur when the temperature reaches Above 20°C, when the humidity dropped to about 60%, the gray mold slowly stagnated. It has been observed that the incidence of heavy rain in winter and spring in Guangdong is heavy; Zhejiang, Shanghai, and Fujian are popular during the rainy season; in mid-November, 1999 in Beijing, the fog continued for several days, and the humidity satisfies the need for disease. At this time, the unheated shed was observed. Room orchid only 15 ~ 17 °C room temperature, not conducive to the growth of orchids, but it is beneficial to the disease of orchid gray mold, so there is a peak incidence. 4. Prevention and control methods (1) Strengthen management and carefully conserve the temperature and humidity of reasonably regulating the environment, especially in the early spring and early winter when the temperature is low and high humidity season, so that the temperature or humidity of the conservation orchids is not conducive to the occurrence of gray mold. The greenhouse or room should pay attention to warming and ventilation to prevent moisture from staying; when watering, do not splash on the flowers. If watering from the top must be done after the morning sun comes out, make the water on the leaves drier. Botrytis cinerea is an airborne disease that removes the sick in time to prevent the spores of pathogenic bacteria from scattering. (2) Spraying 50% procymidone WP or 1500 times iprodione, 50% vinclozolin wettable powder 1000 times, 50% benzene Benomyl WP 1000 times, about 10d once, continuous control 2 to 3 times. The use of 75% chlorothalonil wettable powder 600 times solution and 50% benomyl wettable powder 1000 times solution in the bud stage is more stable. If the disease is severe, it must be used before flowering, and then sprayed again 7 days later. But for colored flowers, benomyl sometimes leaves a faint visible stain. According to reports by Taiwan’s Lu Libiao, orchid seedlings that had just been bottled were sprayed with 58% metalaxyl MnZn WP immediately after transplanting, and 50% metalaxyl granules 25g/m3 were applied on the surface of the cultivation medium. Flower rot hazards. The area where the above fungicides produce resistance can be switched to 65% thiobacillin WP 1 200X or 50% DX (WP carbendazimone) WP 900 times, separated by 10d 1 Times, connect 2 to 3 times. In order to prevent the development of antibiotic resistance, it is advisable to alternate alternation or combination therapy.
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