A Complete Guide to Orchid Pests and Diseases
When it comes to controlling orchid pests and diseases, many orchid growers rush to apply chemicals without first accurately diagnosing what disease or pest their orchids actually have. With this kind of approach, the results are poor. Inaccurate diagnosis is the root cause of severe orchid pest and disease outbreaks.
Main problems in orchid pest and disease control:
1. Inaccurate diagnosis is the root cause of severe orchid pest and disease outbreaks
When it comes to controlling orchid pests and diseases, many orchid growers rush to apply chemicals without first accurately diagnosing what disease or pest their orchids actually have. With this kind of approach, the results are poor. Inaccurate diagnosis is the root cause of severe orchid pest and disease outbreaks.
2. The complex conditions under which orchid pests and diseases occur are the objective reason for severe outbreaks
Because orchid-growing methods vary widely and growers' conditions differ enormously, the environmental conditions for growing orchids are all different; because different growers have different levels of skill, the orchids they grow vary in vigor; and because of all these differences, the environmental conditions under which orchid pests and diseases occur are also very complex, providing ideal conditions for pests and diseases to develop. The end result is that the types of orchid pests and diseases that occur are diverse and vary from one situation to another.
Taking only orchid stem rot as an example: if you rely solely on the single symptom of pseudobulb rot, you cannot make an accurate diagnosis. Even for an experienced person, it is necessary to see the actual plant material, isolate the diseased tissue, and carry out appropriate indoor culturing before an instrument-assisted preliminary conclusion can be reached. For ordinary growers, using only an illustrated guide to orchid pests and diseases may be sufficient for diagnosing insect pests, but when it comes to diagnosing orchid diseases, the conclusions are not necessarily very accurate. Otherwise, orchid stem rot (rot disease) would not be so severe across the country.
3. Insufficient understanding of pesticide characteristics, mechanisms of action, and target organisms
Regarding disease-control chemicals for orchids, many growers only know of two: carbendazim and thiophanate-methyl. When growing orchids, they use these two chemicals for disinfecting plants, for preventing disease, and still use these two chemicals to treat orchids after they become sick. Doing this often leads to losses in years when orchid diseases are severe. This is because both chemicals belong to the benzimidazole class of fungicides, and with long-term use, pathogens easily develop resistance. Moreover, resistance to one of them means resistance to the other is correspondingly developed as well.
Therefore, when using a particular pesticide, you must be clear about its mechanism of action and its target organisms to achieve the corresponding effect. Regarding the mechanism of action of fungicides, you need to understand whether the chemical primarily serves a preventive, therapeutic, or eradicant function against pathogens, and you also need to know whether it has systemic action or contact-killing action, and so on. Only with all this knowledge can you apply chemicals in a targeted way.
In fact, the use of chemicals in orchid pest and disease control is a matter of great refinement. What pest or disease requires what chemical for control must be clearly established. For example, if an orchid bacterial disease is treated with a fungicide meant for fungal diseases, the effect is generally poor or nonexistent; and even for diseases caused by fungi, not just any fungal control chemical will be effective. Targeted use is essential to improve control efficacy. This is the fundamental requirement for chemical use in orchid disease control.
Here, it must be emphasized that a small number of chemicals, such as copper-containing fungicides like copper hydroxide, have some control effect against diseases caused by fungi, bacteria, and viruses. However, these broad-spectrum fungicides are generally used mainly for prevention. When used during a disease outbreak peak, their control efficacy is generally low regardless of what disease is being treated. Relying mainly on such broad-spectrum chemicals to control orchid diseases often leads to significant losses.
4. More attention paid to pests and diseases of the upper and middle parts of orchids, with insufficient attention to pseudobulb and root pests and diseases
From practical orchid-growing experience, many growers pay insufficient attention to pseudobulb diseases and root pests and diseases. In reality, it is the latter two that are most devastating to orchid survival. Most ordinary growers only take action after orchids have already developed pests or diseases and shown symptoms. For pests and diseases of the upper and middle parts of orchids, emergency treatment is often still somewhat effective, but for pseudobulb diseases and root diseases, it is often already too late. Additionally, what growers should pay attention to is the problem of pests in the potting medium. There are many types of pests in the pot, and the damage is in fact quite serious, requiring timely control (the author discusses this in a separate article).
5. Lack of systematic preventive measures and delayed application of chemicals
In orchid-growing practice, we often see people applying one chemical today, then hearing others say another chemical is good tomorrow and switching to that one. As a result, control efficacy is often unsatisfactory. Therefore, to achieve good control efficacy in orchid pest and disease control, for a specific pest or disease, you must use the same effective chemical continuously: for diseases, at least 3 consecutive applications (once every 7-10 days); for pests, at least 2 consecutive applications. Only then can good control efficacy be achieved. Regarding timing, you must apply chemicals when pest populations are still low, which is commonly called "treat early, treat small"; for diseases, you must firmly remember the principle of prevention first and apply chemicals early. If orchids have already developed disease, you must seize the critical period of early onset and apply chemicals continuously. In addition, for pest and disease prevention, you can apply chemicals in advance based on locally common pests and diseases (provided the diagnosis is correct). Keep firmly in mind that the hot and humid season of the year (5-9 months) is the peak period for orchid pests and diseases and requires timely prevention.
Countermeasures:
1. Strictly implement disinfection measures for seedlings and potting media
Newly introduced orchid seedlings must undergo appropriate disinfection, sterilization, and pest elimination procedures to minimize and reduce the transmission of pests and diseases, cutting off sources of spread. When planting orchids, division tools, potting media, and pots should all be disinfected. After many years of practice, the author believes that, apart from the orchids themselves, the best measure is high-temperature sterilization. High-temperature sterilization can kill pathogens and pests and is relatively thorough. Specifically, orchid-growing supplies, tools, and potting media can be boiled in water for 10 minutes, or steamed over boiling water for 30-60 minutes. Other methods such as sun exposure or dry-frying in a pan are also possible, but they may not kill pathogens, pests, and eggs 100%. This is the first step in orchid growing and must be done well.
2. Regular pest and disease prevention
In recent years, with the increase in large-scale and modernized orchid growers, many famous and premium orchids are of very high value, making this point especially important. In mid-August 2005, the author saw on a well-known domestic orchid website that a certain grower, due to stem rot in orchids, lost over 50 plants of the famous premium orchid Chengmei, worth more than 600,000 yuan, within 15 days. This is regrettable. Just think: apart from a few large operations, can the vast majority of growers withstand such a blow? Therefore, doing a good job of orchid pest and disease prevention, especially the prevention of devastating diseases, is very necessary. In terms of specific preventive measures, in Dali Prefecture, generally speaking, spring focuses on pest prevention with disease prevention secondary; the hot and humid summer focuses on disease prevention with pest prevention secondary; autumn involves prevention of both pests and diseases; and in winter, pests and diseases generally occur less, so targeted treatment can be carried out according to individual circumstances. However, in winter, special attention must be paid to protecting the orchid root system. If pot moisture is high in winter, orchids are most prone to root rot. There is a saying in orchid growing: "Nurture roots in winter, nurture leaves in summer and autumn," which makes a lot of sense.
3. Treat the specific problem with the specific remedy
As mentioned earlier, the fundamental reason why orchid pests and diseases are now severe and difficult to control is the failure to treat the specific problem with the specific remedy, which mainly comes down to inaccurate diagnosis. The solution is to do your own prevention and control work well. For pests and diseases you don't know or are unsure about, consult experienced people nearby, or consult experts in this field. Only with an accurate diagnosis can you even begin to talk about treating the specific problem with the specific remedy. Many people nowadays, when discussing orchid stem rot, give the impression of blind men touching an elephant, each blowing their own horn.
4. Timely application of chemicals
This measure mainly includes two aspects: first, prevention and treatment must be timely. In addition to routine preventive work, chemicals should be applied in the early stages of pest and disease occurrence. Second, as mentioned earlier, for the pests and diseases that occur, especially diseases, on the premise of accurate diagnosis, select the right chemical and apply it continuously: at least 3 times for diseases (once every 7-10 days) and at least 2 times for pests, to ensure a certain level of control efficacy. Timely application of chemicals is an effective measure to reduce pest and disease occurrence and minimize losses.
5. Correctly master pesticide concentration and spray evenly
Currently in orchid pest and disease control, there are two incorrect practices regarding pesticide use: first, using excessively high concentrations. For example, some people, when preventing disease, directly apply commercial chemicals undiluted onto the diseased area. For orchids, this method easily causes phytotoxicity (direct phytotoxicity kills the orchid plant; indirect phytotoxicity damages orchid leaves, growing points, and orchid mycorrhiza). For pests and diseases, it easily produces resistance, and the direct consequence is that future use of the same chemical will have poor or no control efficacy. Many people now say that thiophanate-methyl has very poor fungicidal effect, and the reason is prolonged use and improper application methods. Second, some growers, afraid that pesticides will harm their orchids, use very little or use concentrations that are too low, failing to achieve pest and disease control. Both of these methods are actually unscientific. The correct approach is to use chemicals based on each pesticide's mechanism of action, target organisms, and usage methods, combined with your own or others' successful experience, confirming that a certain chemical is effective against a certain pest or disease and causes no phytotoxicity before using it. When spraying, you must spray the front and back of leaves and the potting medium surface to achieve good control efficacy.
6. Alternate chemical use
For the main pests and diseases in a given area, select different types of pesticides. For each pest or disease, choose more than 3 effective pesticides and rotate at least once a month. Only then can you effectively reduce pest and disease resistance, improve control efficacy, and extend the useful lifespan of a particularly effective pesticide. This measure should also draw the attention of all orchid growers.
7. Enhance ventilation
Qu Jinze, a Qing Dynasty orchid grower from Guangdong, said: "In growing orchids, ventilation on all sides is the first principle; ventilation is the foremost task in orchid growing. More sun makes better flowers, more shade makes better leaves; this is said with regard to ventilation. Without ventilation, then with more sun they are scorched to death, with more shade they are smothered to death; none will survive." This is the supreme statement on ventilation in orchid growing, and it is the truth. This requires us to ensure: the orchid-growing environment must be well-ventilated, the potting medium must be loose and air-permeable and rich in nutrients, and the pots must also be well-ventilated, to grow orchids well. Ventilation plays an irreplaceable role in growing orchids well and in preventing and controlling pests and diseases, especially diseases, and every orchid grower should pay attention to it. ---