A Detailed Explanation of the Four Key Principles for Preventing Rot in Orchids in Summer

The foundation of "preventing rot" lies in "knowing rot." Understanding and mastering the causes and harmful characteristics of soft rot and stem rot is the key element in preventing and treating "rot disease." There are often orchid growers who cannot distinguish the damage caused by soft rot and stem rot, leading to prevention and treatment work that misses the point and fails to hit the mark, thereby delaying diagnosis and treatment and resulting in major losses. So let us uncover the true face of "rot disease"!

Soft rot: Research results in ornamental plant pathology show that soft rot in Chinese orchids (Cymbidium) is a bacterial disease, with the pathogen being Erwinia carotovora. Symptoms first appear on new shoots, and within a week the orchid plant is infected and dies, with severe cases causing the entire pot of plants to collapse; some orchid plants are robust with strong resistance, so the disease appears milder and does not cause the whole pot to die. The characteristic is thatorchid plantsfirst develop water-soaked lesions at the stem base or upper root area, pale grayish-yellow, with the plant tissue becoming sticky, wet, and rotting, turning into a mushy state with a foul odor. The lesions spread upward, downward, left, and right, causing the stem base, roots, and leaf bases to rot. Because the tissue at the stem base becomes brittle after being damaged, the orchid leaves detach very easily, coming off with a gentle pull, and in the late stage of the disease the affected plants topple over on their own.
Stem rot: Stem rot in Chinese orchids (Cymbidium) is a fungal disease, with the pathogen being a fungus of the order Sphaeropsidales in the class Deuteromycetes. Symptoms first appear chronically on the parent generation or an even earlier generation of plants, with the disease period lasting a month or even half a year. After the plant is infected, the initial symptom is the stem base turning brown, the leaves losing their green color and drooping slightly downward. After the diseased area rapidly develops upward, the entire plant dies, with the leaves drooping but not falling off. The cortex of the diseased stem shrinks and wrinkles, and the epidermal tissue rots into a spongy state. After the disease spreads to the roots, the root cortex rots. In the late stage of the disease, some leaf bases still retain some toughness but have already lost water and shrunk, while some leaf bases turn yellow, becoming extremely brittle and easily broken.

2. Strengthen Ventilation

The key to preventing and treating orchid diseases in the high-temperature, high-humidity summer environment lies in ventilation and air permeability, just as the ancients said, "In growing orchids, ventilation on all sides is the first priority." Orchids are like people: if a person is in a stuffy environment for a long time, they are also prone to illness; if an orchid garden is poorly ventilated, the orchids will surely be steamed and stifled in the hot summer, making them highly susceptible to diseases such as soft rot and stem rot! On my balcony I set up two orchid racks, placed on the left and right sides of the living room doorway. The three pots of soft rot patients I found this year were Baodao Jinlong, Yuzhen Dagongsu, and Shizhang Hong, one shoot each, all located on the right-side orchid rack. The main reason is that the ventilation on that rack is not as good as on the left rack. Therefore, when creating an orchid-growing environment, one must do everything possible to achieve ventilation and air permeability, keep the orchid garden clean and orderly, and place orchid pots suspended on orchid racks. It should be noted that ventilation does not only refer to the airflow in the balcony or orchid room under the blowing of a fan; it also needs to take into account the loose and air-permeable nature of the growing medium, the breathability of the orchid pot, and it must not block the respiration of orchid roots, otherwise disease is also likely. Orchid growers easily notice a phenomenon: it is generally very difficult to grow orchids well in an office, because after work hours and on weekends the office is often closed up, ventilation is poor, and once the weather gets hot, orchid diseases are prone to occur. To grow orchids well in an office, solving theorchidventilation and air permeability problem becomes the key.

3. Appropriate Dry Cultivation
Dry cultivation and wet cultivation are orchid-growing methods defined relative to the frequency and amount of watering by orchid growers. I conducted a rough survey of orchid growers, and the conclusion was: beginners mostly use wet cultivation, while veterans mostly use dry cultivation. This is consistent with the saying "beginners easily drown them, veterans easily dry them out." In the orchid world, debates often arise over whether "wet cultivation is better" or "dry cultivation is better," but unfortunately no conclusion is often reached. So generally speaking, which method is actually more suitable for growing orchids? I believe that choosing dry cultivation or wet cultivation, besides varying from person to person, crucially varies with the season! In my case: in spring and autumn, I lean slightly toward wet cultivation; in summer and winter, I lean toward dry cultivation. The greatest benefit of dry cultivation in summer is that it can reduce the occurrence of diseases such as soft rot and stem rot to a greater extent. Some orchid growers summarize it as: "Dry cultivation leads to fewer diseases, wet cultivation leads to more diseases." I believe that leaning toward dry management can, first, increase the opportunity to implement sunlight sterilization in the growing medium environment; second, reduce the possibility of pathogens spreading in a thoroughly wet growing medium environment. In addition, practice has proven that dry cultivation also has the practical effects of strengthening shoots, promoting flowering, and growing roots. So what is the standard for dry cultivation? To what degree of dryness or aridity is it appropriate to water? So-called "dry cultivation" is a management method in which watering is done only one or two days after the surface soil of the pot has dried slightly white. The ancients' method was to use a thin bamboo strip to push aside the growing medium on the pot surface and look at the roots; when the roots at the bottom were seen to be dry, then it was time to water. Some orchid growers do not push aside the pot soil, but instead look at the roots growing on the pot surface and exposed outside the growing medium; when the roots on the pot surface are seen to be shriveled, they water, or they practice withholding water, that is, waiting two or three more days before watering. This method can also be used for reference.
4. Use Medication According to the Symptoms
The principle for dealing with orchid diseases is "combine prevention and treatment, emphasize prevention, and carry out comprehensive management." In addition to the preventive measures of "strengthening ventilation" and "appropriate dry cultivation" mentioned above, my prevention and treatment measures in orchid management mainly include: First, in daily management, alternately use medications for preventing and treating bacterial and fungal diseases, spraying or drenching to prevent the occurrence of rot. Second, spread plant ash to prevent soft rot. During the summer plum rain season, using plant ash, rice husk charcoal, or quicklime, spread it on the pot surface to effectively prevent the occurrence of soft rot. Third, do a good job of disinfection when preparing pot soil. In view of the habit of bacteria and fungi parasitizing in pot soil, thoroughly disinfect each type of planting material when preparing the growing medium, ensuring it is clean and sterile, leaving no future trouble.

Of course, in the practice of orchid cultivation, even the most rigorous prevention will still have oversights, which leaves room for the breeding of "rot disease." Once a potted plant is found to be diseased, do not panic; think calmly about a treatment plan and immediately take decisive measures. First, remove from the pot and clean the plants. Discard the pot and pot soil, cut off and destroy the diseased plants, wash and clean the healthy plants, and accurately determine based on the symptoms whether it is soft rot or stem rot. Second, thoroughly disinfect. If it is soft rot, use bactericidal medication for disinfection; you may choose a 1000-fold solution of one of the following: carbendazim, agricultural streptomycin, chloramphenicol, potassium permanganate, or amobam, soak for 30 minutes, then rinse with clean water and air-dry. If it is stem rot, then use fungicidal medication for disinfection; you may choose a 1000-fold solution of one of the following: thiophanate-methyl, difenoconazole, carbendazim, azoxystrobin, or metalaxyl. Third, replant and cultivate cleanly. After the plants are air-dried, replant them in a new pot with new soil, place them in a cool, ventilated area to recover, and you may regularly spray fungicide on the leaves or drench the roots. To be safe, for prized plants it is best to choose the method of dividing and replanting individually, in order to prevent mutual infection among orchid plants.