Cymbidium orchids require a relatively high humidity level, typically 80% to 90%, to thrive in optimal environments. However, high humidity coupled with poor ventilation, stagnant air, and insufficient light can lead to the occurrence and spread of pests and diseases. The main pests and diseases commonly found in this region are described below:  

I. Diseases: The main diseases include blight, soft rot, root rot, anthracnose, leaf blight, and toxin diseases.  

epidemic

Depending on the location and symptoms, diseases like blight are classified as black rot, heart rot, stem rot, and damping-off, and can occur year-round in the Xiamen area. High temperatures, excessive watering, and poor ventilation in greenhouse cultivation can lead to water accumulation in the leaf tips, making the plant more susceptible to this disease over time. The peak incidence is from June to August each year. Seedlings and flowering plants can be affected, especially clustered seedlings and new buds and heart leaves. It is caused by two closely related fungi—Phytophthoracactorum and Pythium wilfordii. Phytophthoracactorum easily causes root rot, damping-off, and root collar rot, while Pythium wilfordii also easily causes root rot and damping-off. If these diseases are not treated promptly, they quickly spread to the roots and bulbs, making them a devastating disease for Cymbidium orchids. The transmission route is through spores spread by splashing water droplets during watering.  

Prevention and control methods:  

1. Environmental control: The orchid greenhouse should be well-ventilated and have sufficient light. When disease occurs, watering should be strictly controlled, and diseased leaves and plants should be removed promptly. At the same time, avoid spraying water from top to bottom.  

2. Once a diseased plant is found, immediately remove the diseased tissue and cut off about 1 inch of uninfected tissue. If the plant is severely affected, remove the entire plant.  

3. Scissors and other utensils must be strictly disinfected.  

4. Chemical treatment: Spray with a 500-fold dilution of 80% zinc manganese acetonitrile. Alternatively, spray with a 1:2000 solution of 8-hydroxyquinoline sulfate, or soak the diseased plants in a sodium o-phenylphenol solution for 1 hour. Repeat the treatment within 3 to 7 days if necessary.  

Soft rot

Soft rot typically affects the leaves, buds, and bulbs of Cymbidium orchids, and can occur from spring to autumn, with less frequent occurrence in winter. It sometimes co-occurs with blight, but is less severe. It is caused by a bacterium called *Erwinia chrysanthemum*, which has a wide host range and can infect any orchid species. Its entry route is mainly through wounds or natural stomata. In hot and humid orchid greenhouses, the disease spreads extremely rapidly. At 100% relative humidity and 30°C, the infection process is completed within three hours after artificial inoculation. Its symptoms are somewhat similar to blight, making it difficult for novice orchid growers to distinguish between the two. Because these two diseases are different in nature, the medications used are also different. In the field, our main method of identification is based on observing the rotten parts of the diseased tissue: the rotten tissue of blight has little or no sap, no fishy odor, and when a drop of sap is squeezed into a glass of water, no cloudy turbidity is observed spreading; while the cells in the epidermis of the diseased part of soft rot are decomposed into a watery liquid containing countless white bacterial mud, with a lot of sap, which flows out with the slightest touch, and has a fishy odor. When a drop of sap is dropped into a glass of water, a cloudy turbidity can be seen spreading in all directions.  

Prevention and control methods:  

1. Environmental control and treatment of diseased plants: Same as item (a) above, but pay special attention to prevent the sap from the fungal sludge from contaminating healthy plants. 

2. Chemical Treatment: Common pesticides are ineffective against soft rot, so once the disease develops, infected plants must be discarded. Therefore, preventative measures are crucial. Spraying with a 40% solution of cypermethrin at a dilution of 400 times is quite effective. Alternatively, a 1000-fold dilution of 68.8% propiconazole or 18.8% streptomycin can be used, spraying once every 7 to 10 days for 3 to 4 consecutive applications. These pesticides can be used alternately to prevent the plants from developing resistance.