orchid rot

1. Harm: orchid flower rot has been found in Guangzhou, Nanjing, Shenzhen and other places. It is also common abroad, such as the United States, Singapore, Thailand and other countries. The disease can damage a wide range of orchids, including Phalaenopsis, Caterpillar, Dendrobium, Dendrobium and Cymbidium, among which Dendrobium and Cartland are more susceptible. However, the flowers of Orchid and Phalaenopsis are more resistant to the pathogenic fungi.

2. Symptoms: the spots on orchids are similar to those on mast flowers, cyclamen, chrysanthemums, carnation and geraniums. Small translucent water stains occur 24 hours after the petals and flowers are infected. As the spot turns brown, there is sometimes a light pink around the spot. The number of disease spots on each flower varies, but as soon as the flowers begin to wither, the disease spots will increase. Careful examination will find that there are fluffy growth on the flowers, which are the hyphae and spores of Botrytis cinerea. The asexual generation of germs is most commonly observed.

3. Pathogen: the pathogen of orchid flower rot is generally considered to be Botrytis cinerea. Conidiophores single branch or even dendritic branches, tip dilated or pointed, with small protuberances, conidia solitary on small processes, spherical, oval or cylindrical, single cell colorless or pale. Arising from sclerotia or hyphae in the body, conidiophores 280~350umX12~24um, tufted, gray and then brown. Conidia are subglobose or ovoid, 9~15umX6.5~10um, but some cases are complicated. It is reported that natural sporulation can not be seen from natural collected specimens of Dendrobium orchid rot. Among the 27 strains isolated, their spore morphology is obviously different, according to which they are divided into three types. Among them, 2 strains belong to type 1, which are B.cinerea, the spores are oval, the size is 10.0umX7.7um, and 13 strains belong to type 2, more than 94% of the ellipsoids are in the size of 17.3umX12.2um, of which about 1% and 6% are double spores. There are 12 strains of dish type, whose spores are gyro-shaped single spores similar to 2 spores, 19.6umX10.8um in size, but it also has 3% 14% gyro-shaped spores, length 15.4um, widest point width 14.6um, gyro-shaped spores have a series of multiple shapes, some are close to Obovate, wedge-shaped, gyro-shaped and lobular, and the types of 2 and 3 strains have not been identified.

4. Characteristics of disease: most of orchid flower rot produces conidia in rotten flowers, and many conidia are produced from rotten flowers. When the air is cold (7-18 degrees), or the orchid room is poorly ventilated, the flowers are often attacked by orchid flower rot, resulting in the prevalence of the disease. In other seasons, when the temperature is high, the disease is generally limited to older and withering flowers, and all kinds of orchid flowers can be infected with the disease when the flowers begin to senescence or have begun to weaken. The conidia of the pathogen are transmitted by water or air. When fertilization, the rapid growth of leaves and wet and cool conditions are conducive to the occurrence of the disease.

5. Prevention and control methods:

(1) strengthen quarantine: orchid flower rot is relatively rare in China, and the incidence is not as serious as abroad. When orchids are imported, quarantine measures should be strengthened to prevent germs from being brought in.

(2) Horticultural control: pay attention to ventilation in the orchid room, watering must be careful not to water the flowers, if watering from the top, it should be carried out in the morning to make the leaves dry as quickly as possible.

(3) artificial control: remove and destroy all diseased flowers and other infected parts, this measure can reduce the number of infection sources formed by bacteria through saprophytic growth.

(4) Chemical control: new flowers are highly susceptible, so it is necessary to use fungicides with long efficacy. The available agents at this stage are chlorothalonil, carbendazim, zinc separated from the first generation manganic complex and RP26109. When used in the old bud stage, chlorothalonil and carbendazim are more stable in protection than the other two drugs, but chlorothalonil can leave residue on the flowers. In addition, it is also toxic to plants. Therefore, attention should be paid to the use. Its concentration is as follows: chlorothalonil: 180g/100L, carbendazim: 30g/100L, RP26019: 20g/100L, zinc separated from the first generation of Manganese mixture (carbamate disulfide): 192g/100L. In addition, the application of 50% wettable powder has a good effect, with a concentration of 1000 times, once every 30 days. If orchid flower rot has become a problem, it must be sprayed on the flower before flowering, and then the above proportion must be applied 7 days later, but for colored flowers, benzoate may leave a faint visible stain. Taiwan's Lu Liyan reported that freshly released orchid bottle seedlings were sprayed with 58% metalaxyl manganese zinc (mn-Zn minus Daryl) wettable powder 600 times after transplanting, and 5% metalaxyl granules were applied on the surface of the planting medium. 25g petal m 'could control the harm of orchid flower rot. The application of metalaxyl manganese zinc alone can control the incidence rate within 3%, but it is not as effective as the combined use of the two agents. 5% of metalaxyl granules can be used repeatedly with an interval of 8 weeks, and the control effect can also reach 100%. Metalaxyl granule can be applied once when planting in the field, metalaxyl and metalaxyl manganese and zinc are applied according to the above method if the bottle seedling is used, and metalaxyl granule is applied again after 6 weeks and 8 weeks. In the dry and cold season with less incidence, the drug can be used once every 3 to 4 months, and the disease prevention can be achieved by using it 4 times a year. (Liu Zhongjian)