Comprehensive Prevention and Control Methods for Stool Rot Disease in Chinese Cymbidium

1. Select disease-free seedlings Since Fusarium parasitizes the soil (potting medium), the pathogen often adheres to the roots and pseudobulbs of orchid plants. When orchid plants are divided and replanted, the pathogen invades through the cut surfaces and causes disease. We oftenorchidssee in growing operations that orchids which originally had stool rot become more severely affected after division. For example, at the Lunjiao Sanzhou orchid farm in 2003, 45 out of 420 pots had stool rot, a rate of 10.7%. When these seedlings were planted in 1,000 pots in 2004, 128 pots had stool rot, a rate of 12.8%. In contrast, orchids that originally had no stool rot rarely developed the disease after division - the distinction is as clear as black and white, without ambiguity. Some new areas that had never grownorchid plantsbefore contracted this disease after introducing a batch of orchids with stool rot. Ten years ago this disease was rarely seen in mainland China. Due to the rise of theorchidmarket,orchid plantscirculate as a traded commodity, spreading through growing media, pots, seedlings, and human handling. After planting, it further spreads through splashing from fertilization and watering, insect feeding, and human operations. Before purchasing orchid seedlings, we need to observe whether the nursery has had occurrences of stool rot, and we must buy seedlings from healthy, disease-free nurseries. Large-scale growing operations should ideally establish a system of self-propagation, self-cultivation, and self-supply of healthy seedlings, rather than purchasing orchids from many different sources. For example, the Taohong Orchid Farm in Shawan, Panyu, Guangzhou, started from a single plant ofFour SeasonsOrchid'Xiao Taohong' and self-propagated to 500,000 seedlings over 13 years, with no stool rot in the entire operation. In Guo Genquan's balcony orchid nursery in Lunjiao, Shunde, 3 pots of 'Xiao Taohong' were self-propagated and self-cultivated to 1,500 pots, and stool rot was never observed. 2. Clean and disinfect seedlings; use disposable growing media and pots Whenorchid plantsare divided and planted, pull up the plants, rinse them clean with clean water (tap water), remove attached floating mud, and place them in a cool, shaded spot for half a day to cool, then divide. When dividing, twist apart the connection point between two plants by hand. For those growing a small number of orchids, use a brush to apply 70% thiophanate-methyl powder directly to the cut surfaces. For large quantities of orchid plants, spray the cut surfaces and roots with 70% thiophanate-methyl at 1:500 dilution, and let them dry in a cool place for half a day before planting. This seedling disinfection method can reduce the invasion of pathogens through cuts and wounds. All old growing media must be discarded. Never mix new and old media when planting orchids, to avoid spreading and disseminating pathogens. Pots should also be new. Plastic 16*16 growing bags cost only one jiao each, so the cost is not high. If valuable pots are too precious to discard, they must be exposed to sunlight for a period, then disinfected with chemical solution before use. 3. Improve planting methods: (1) Change from dividing orchids once a year to once every two years. This reduces infection from division cuts and also improves the overall resistance of the plants. Under the samecultivationconditions, a fixed-point survey in 2004 showed that two-year-old orchids in 958 pots had a stool rot rate of 3.34%, while newly planted one-year-old orchids in 2,036 pots had a stool rot rate of 7.12%. (2) Change from single-plant planting to clump planting. To increase propagation rate, dividing orchids into single plants is counterproductive, for the reasons stated above. (3) Change from spring planting to autumn planting. In South China, planting orchids in September in autumn makes it easier to survive and less prone to disease than planting in February or March in spring. This is because autumn temperatures are around 25°C-28°C, and newly planted orchids develop new roots and grow within one month. Once new roots are established, they enter winter and spring, and in spring they sprout early and vigorously. In spring, rainy days make the soil and potting mix too wet, which easily breeds pathogens that invade cuts and transmit disease. This is especially true forFour SeasonsOrchid. Autumn-planted orchids show significantly better propagation rates and growth than spring-planted ones. Orchid farms dealing inCymbidium sinensecommercial stock are also gradually shifting to primarily autumn planting. 4. Improve fertilizer and water management Within one month after planting orchids, do not pour too much water, to avoid damaging old roots. Sprinkle water on the leaves and keep the surface soil moist but not dry. During May and June, when stool rot is most prevalent, avoid large amounts of watering and liquid fertilizer application. Instead, focus on spraying leaf surface water and foliar fertilizer to reduce splashing and spread of fertilizer water and disease. In winter and spring, do not apply un-decomposed organic fertilizer. It is best to use slow-release fertilizers such as "Haokangduo" and "Osmocote," 3 grams per pot, with fertilizer effect lasting half a year, slowly releasing for plant absorption. In our experiments, applying effective microorganisms (EM) in spring at 8 grams per pot not only kept orchid plants growing healthily with emerald green leaves, but also reduced disease. EM contains more than 20 groups of beneficial bacteria, which may have an inhibitory effect on harmful bacteria. 5. Improve the ecological environment; clean the orchid garden Orchid plants prefer ventilated and humid environments. Ancientorchid growersconsidered ventilation the first priority. Around the orchid shed, 1 m above ground level, openings should be made for ventilation. In Guangdong, from winter and spring to early summer, that is from November to May of the following year, cover one layer of 75-85% shade netting to let the orchid nursery receive more light. In a ventilated and light-transmitting environment, harmful substances and harmful organisms are less likely to accumulate and breed. From June to October, double-layer shade netting is needed. Promptly remove plant debris from the orchid nursery to reduce pathogen attachment. Especially when diseased plants are found, they must be immediately removed and disinfected to reduce sources of infection. In spring, apply slaked lime powder at 100 jin/mu 1-2 times, directly scattering the powder over the entire orchid garden. When the powder adheres to leaves, even the three-pronged parts and pseudobulbs, it can have a disinfecting effect, and it will not burn orchid leaves or plants. 6. Apply appropriate pesticides I have conducted prevention and control experiments with more than 20 pesticides. The relatively effective ones are: (1) Copper-based preparation 1:2:100 Bordeaux mixture; (2) 70% thiophanate-methyl 1:800 dilution; (3) Daconil 1:300 dilution; (4) Agricultural streptomycin 1:400 dilution; For the above pesticides, the spray volume per mu is 300 jin of solution, sprayed 2-3 times per month from March to June. According to reports from Taiwan, China, Prochloraz-MN at 1:4000 dilution has a special effect. Some orchid farms respectively use Jinggangmycin (1:400 dilution), sulfur water (5 parts per ten thousand), and sulfur suspension (1:400 dilution), pouring them into the potting soil before disease onset, 1-2 times per month. These orchid farms have less stool rot, which can be used for reference. Excerpted from "TheOrchidTreasure Book" Author: Hu Yingdong, Shunde, Guangdong