A small plant knowledge, introducing everyone to the experience of the flower clinic in the aspect of butterfly orchid, the gray mold disease of butterfly orchid and its prevention and treatment, let's follow the editor to see!
Orchid gray mold disease is also known as orchid flower rot. It occurs occasionally in flower gardens in the south and north of China, in addition to harming orchids in the orchidaceae family, it also harms flower plants such as Phalaenopsis, Cattleya, Dendrobium, Vanda, and Cymbidium. Among them, butterfly orchid, large flower Cymbidium, and black orchid are more seriously affected.
1. Symptoms
The gray mold disease of butterfly orchid mainly affects the flower organs, sepals, petals, and peduncles, and sometimes also affects the leaves and stems. In the early stage of the disease, after petals and sepals are infected, small transparent water-soaked spots can be produced within 24 hours, followed by the spots turning brown, and sometimes there are white or light pink circles around the spots. The number of spots on each flower varies, but when the flowers begin to wither, the spots increase rapidly, and the petals become blackish-brown and rot. When the humidity is high, fluffy, mouse-gray growth appears on the腐烂 flowers, which is the pathogenic fungal conidiophores and conidia. When the peduncle and stem are infected, small water-soaked dots appear in the early stage, gradually expanding into round to oblong spots, black-brown and slightly sunken. When the spots expand to encircle the stem, the flower dies. When it affects the leaves, the leaf tips become withered. The disease usually appears in 2-3 peaks in early spring and autumn and winter each year. In severe cases, the flowers are covered with disease spots, and gray mold is everywhere, which is a devastating disaster for orchids that are more appreciated for their leaves than their flowers or specifically for their flowers. When the temperature is high, the disease is limited to older flowers that are withering. Many orchids can be infected when they start to age or become weak.
2. Pathogen
The pathogen of the disease has been identified as Sclerotinia fuckeliana (de Bary) Fuck, belonging to the Ascomycetes. Its asexual state is Botrytis cinerea Pers. ex Ff., known as gray grape mildew, belonging to the Hyphomycetes. Under adverse conditions, sometimes lamellar sclerotia are produced on the diseased parts, with the surface of the substratum, varying in size, mostly 3-4.5 mm × 1.8-3 mm, with the smallest diameter being 1 mm. On Czapek's medium, the sclerotia are semi-buried mostly, 2.5-15 mm in size, round to oblong. The sexual spore stage is common, with white antheridium, grayish-white colonies, and spherical sexual spores, 3-4 micrometers in size. The asexual colonies are initially grayish-white and later brown. Conidiophores are scattered or clustered within the colonies, light brown to brown, septate, 280-350 micrometers × 12-24 micrometers in size, with apical 1-2 branching, slightly swollen, some club-shaped, densely covered with small pedicels, and producing a large number of conidia. Conidia are broadly ovate, numerous, unicellular, nearly colorless, 6-8 micrometers × 5-12 micrometers in size. Under scanning electron microscopy, the spore surface is smooth. In addition to infecting orchids, the fungus can also infect bulbs, cyclamen, marigolds, snapdragons, begonias, cinerarias, caladiums, cannas, clitoria, crinums, daylilies, hibiscus, gladioli, dwarf morning glories, hippeastrum, chrysanthemums, marigolds, poinsettias, camellias, forsythias, roses, cherry blossoms, azaleas, salpiglossis, calla lilies, and many other flowers.
3. Transmission途径 and Incidence Conditions
The pathogen overwinters in the soil as sclerotia at depths of 5-12 cm. In the following spring, when the temperature is 7-8°C and the relative humidity is above 88%, a large number of mycelium and conidia are produced on the sclerotia, which are then spread by air currents, water droplets, dew, and horticultural operations. The expansion of the disease is gradual, and after the seedlings are infected, the pathogen can establish itself. It often expands with the growth of the plant, first affecting the stems or leaves or latent, and once the flowers bloom and the conditions are suitable, the flower organs quickly become infected. The occurrence of gray mold is greatly influenced by the incidence conditions. Sclerotia can germinate at temperatures between 5-30°C, requiring only 1 day at 21°C and 5 days at 5°C. The starting temperature for mycelium development is 2°C, with the highest at 31°C, and 20-23°C is the most suitable. The optimal temperature for spore germination is 18-24°C, with 72.6% germination rate after 24 hours at 21°C, and only a few spores germinate after 24 hours at 35°C, with no germination at 37°C. The fungus is more strict in humidity requirements than temperature, with spores unable to germinate below 84% RH, and only able to germinate normally above 88%, with the highest germination rate at 92-95% RH. It takes 15 days to produce conidia at 80% RH, and only 3 days at 100% RH. In addition, high humidity is favorable for pathogen invasion, expansion, and prevalence, and the incubation period can also be shortened. The pathogen requires certain nutrients to infect, such as withering petals or pollinated stigma, and wounded stems and leaves are easily infected by gray mold. After infection, the fungus first becomes saprophytic, and then infects healthy flowers or stems after forming a population.
The disease often requires a process of pathogen accumulation to流行 in orchid nurseries or greenhouses. The main infected parts of butterfly orchid gray mold are the sepals, petals, and stigma, with the source of the pathogen being withering flowers. Therefore, the weather conditions during the flowering period of orchids have a significant impact on the disease. When the temperature is 7-18°C and the RH is above 88%, the disease is easily onset. In plastic greenhouses, solar greenhouses, and living rooms, the relative humidity can often meet the requirements for the disease, while indoor temperature is the limiting factor for the prevalence of the disease. When the number of days with temperatures below 18°C is high, gray mold begins to occur, and when the temperature reaches above 20°C and the humidity drops to around 60%, the disease slows down. Observations show that the disease is severe in Guangdong during the continuous rainy season in winter and spring; in Zhejiang, Shanghai, and Fujian, it is easy to prevail during the plum rain season; in November 1999, Beijing experienced several days of heavy fog, with humidity meeting the requirements for the disease, and the temperature in the unheated greenhouse nurseries was only 15-17°C, which was unfavorable for orchid growth but favorable for the prevalence of gray mold, thus causing another peak of the disease.
4. Control Methods
(1) Strengthen management, careful nursing, reasonable regulation of environmental temperature and humidity, especially in the low temperature and high humidity seasons of early spring and early winter, to make the temperature or humidity of orchid care unfavorable for the occurrence of gray mold. Pay attention to heating and ventilation in greenhouses or living rooms to prevent moisture buildup; when watering, do not splash water on the flowers, and if watering from the top, it must be done after the sun comes out in the morning to allow the water on the leaves to dry faster. Gray mold is an airborne disease, so it is necessary to remove diseased debris in time to prevent the spread of spores.
(2) Chemical control: At the beginning of the disease, spray 50% procymidone wettable powder 1500 times liquid or 50% iprodione, 50% vinclozolin wettable powder 1000 times liquid, 50% benomyl wettable powder 1000 times liquid, about every 10 days, for continuous control 2-3 times. The efficacy of 75% chlorothalonil wettable powder 600 times liquid and 50% benomyl wettable powder 1000 times liquid is stable in the old bud stage. If the disease is severe, it is necessary to use medicine before flowering, and spray again after 7 days, but benomyl may leave a faint visible stain on colored flowers. According to the report by (T-W) Lyu Laiyan, after the orchid seedlings are transplanted, immediately spray 58% metalaxyl-manganese zinc wettable powder 600 times liquid, and apply 50% metalaxyl granules 25g/m³ on the cultivation medium surface, which can control the damage of flower rot. In areas where resistance to the above fungicides has developed, 65% thiophanate-methyl wettable powder 1200 times liquid or 50% polyoxymethylene (polyoxymycin) wettable powder 900 times liquid can be used, every 10 days or so, for 2-3 times. To prevent resistance and improve control efficacy, it is recommended to alternate or mix different fungicides.
That is the specific introduction of butterfly orchid gray mold disease and its prevention and treatment, hoping to bring some knowledge of flowers to flower enthusiasts.