How to prevent and control common pests and diseases of Cymbidium orchids?

Japanese hybrid large-floweredCymbidiumhas been cultivated at the Xiamen Overseas Chinese Introduction Garden and the BinfenOrchidFarm and other sitesfor16 years of cultivation history. During thecultivationprocess, many diseases, insects, and small animal pests have been encountered. As a researcher, I have summarized the observed and recordedpest and diseasesituations and control measures, and provide them here as a reference for orchid growers. When large-floweredCymbidiumis cultivatedin a good ecological environment, it has relatively high requirements for air humidity, generally requiring relative humidity to reach 80% to 90%. However, when humidity is high, if ventilation is poor, air does not circulate, and light is insufficient, it can also cause the occurrence and spread ofpests and diseases. The main commonpests and diseasesin this region are described below: I. Diseases: mainly including Phytophthora blight,soft rotdisease, root rot, anthracnose, leaf blight, viral disease, etc. (1) Phytophthora blight: Because Phytophthora blight occurs in different parts and produces different symptoms, it is also divided by people into black rot, heart rot, stem rot, damping-off, etc. In the Xiamen area, it can occur in all fourseasonsof the year. Under greenhouse cultivation conditions with high temperature, excessive watering, and poor ventilation, a large amount of water accumulates in the leaf tips, and over time this most easily triggers the disease. June to August each year is the peak period of onset. From seedlings to flowering plants, all can be affected, especially clustered seedlings and new shoots and young leaves are most vulnerable. It is caused by two closely related fungi - Phytophthora cactorum and Pythium ultimum. Phytophthora cactorum easily causes root rot, damping-off, and root crown rot, while Pythium ultimum also easily causes root rot and damping-off in plants. Once these diseases occur and are not treated promptly, they quickly spread to the root system and bulbs, so they are terrifying and destructive diseases of large-floweredCymbidium. Their transmission route is through spores spreading and dispersing via water droplets splashed during watering. Control methods: 1. Environmental control: The orchid shed should be well ventilated and allow sufficient light. During disease onset, water must be strictly controlled, diseased leaves and diseased plants should be removed promptly, and watering from above downward should be avoided. 2. Once infected plants are found, immediately remove the diseased tissue, and at the same time cut away about 1 inch of uninfected tissue as well; if the damage is severe, remove the entire plant. 3. Tools such as scissors must be strictly disinfected. 4. Chemical treatment: spray with 80% zineb 500-fold solution. A 1:2000 solution of 8-hydroxyquinoline sulfate may also be sprayed, or the diseased plants may be soaked in sodium orthophenylphenate solution for 1 hour, and if necessary, repeated treatment may be carried out within 3 to 7 days. (2)Soft rotdisease: Soft rotdisease usually attacks the leaves, shoots, and bulbs of large-flowered Cymbidium. It can occur from spring to autumn throughout the year, and is less often found in winter. Sometimes it occurs together with Phytophthora blight, but is not too serious. It is caused by a bacterium called Erwinia chrysanthemi, which has a very broad host range and can harm all orchid plants. Its route of invasion is mainly through wounds or natural stomata. In orchid sheds with high temperature and high humidity, this disease spreads extremely quickly. At 100% relative humidity and a temperature of 30°C, after artificial inoculation, the invasion process is completed after 3 hours. Its symptoms are somewhat similar to Phytophthora blight, making it very difficult for beginnerorchid growersto distinguish. Because these two diseases differ in nature, the medications used are also different. In the field, our identification is mainly based on pulling out the rotten diseased part for observation: the rotten tissue of Phytophthora blight has no sap or little sap, no fishy stench, and when a drop of sap is squeezed into a cup of clear water, no cloud-like turbid matter is found spreading; while in soft rot disease, the cells inside the epidermis of the diseased part are all decomposed into watery liquid containing countless white bacterial ooze, with abundant sap. With a light touch, the sap flows out, and at the same time there is a fishy stench. When a drop of the sap is dripped into a cup of clear water, cloud-like turbid matter can be seen spreading around. Control methods: 1. Environmental control and handling of diseased plants: same as item (1) above, with special attention not to let the sap of bacterial ooze contaminate healthy plants. 2. Chemical treatment: general pesticides are ineffective against soft rot, so once the disease occurs, the diseased plants have to be discarded. Therefore, preventive measures are mainly adopted; spraying with 40% Kocide 400-fold solution gives good results. A 1000-fold solution of 68.8% doxycycline-streptomycin or 18.8% streptomycin may also be used, sprayed once every 7 to 10 days for 3 to 4 consecutive times. These chemicals can be used alternately to prevent the plants from developing pesticide resistance. (Wu Lianxing)