What to Do When Chinese Cymbidium Gets Phytophthora Disease? A Detailed Guide to Prevention and Control

Phytophthora disease is the most common disease of Chinese Cymbidium. Chinese Cymbidium grown long-termcultivationin high-temperature, high-humidity, poorly ventilated greenhouse facility environments is most susceptible to Phytophthora disease. This is also the period with the highest frequency of Phytophthora disease occurrence, especially from the budding stage to the growth stage. The pathogen species of Phytophthora disease can be divided into Phytophthora and Rhizoctonia-like forms that infect orchid plants, and belong to soil-borne transmission diseases. After the Phytophthora pathogen infects orchid plant tissues, the lesions are initially dark green, and the lesions expand extremely rapidly, and can occur on any part of the orchid plant. From the young bud stage to leaf unfolding, because thecultivationmanager does not immediately keep the above-ground part of the orchid plant dry when performing watering work, water accumulates in the bud core and bract leaves, and the Phytophthora pathogen takes the opportunity to invade and cause damage, with the leaf core rotting like water soaking. At this time, if thecultivationmanager cannot immediately take prevention and control measures and remove diseased leaves, the lesions will rapidly expand and spread to the pseudobulbs and root base. In severe cases, it will spread to other healthy orchid plants. At the mature stage of the orchid plant, because the leaves have matured and the tissues have become fibrous, after infection by Phytophthora disease, they will not rot and topple, only showing leaf yellowing. In severe cases, the yellowing extends to the finger ring (abscission layer), the leaf door falls off, and the roots are damaged. Sometimes a diseased plant that has lost all its leaves will grow new shoots from the bulb. If the roots are infected by the Phytophthora pathogen, the root tissues rot, and the pathogen will spread upward, damaging the bract leaves and growth point, severely causing necrosis of the bract leaves and growth point. Transmission routes: The Phytophthora pathogen occurs most severely under high-temperature, high-humidity or poorly ventilated environments. When relative humidity reaches 100 percent, the disease spreads rapidly; the pathogen slows down as humidity decreases, and at 50 percent relative humidity the pathogen stops growing. The Phytophthora pathogen can be transmitted by water, wind, and media. The rainy season is the period with a higher incidence of Phytophthora disease, and insects can also transmit Phytophthora disease. Prevention and control methods: (1) Maintain good ventilation in the orchid room, avoid overwatering and leaching that cause the medium to become acidified. The medium selected must have good drainage and rewet quickly. (2) After watering the leaves, they should be kept dry immediately to avoid water accumulation in the bract leaves and bud core. There are a few swimming spores that can invade and cause infection even without wounds. (4) Always pay attention to pest insects to avoid the spread of Phytophthora disease. (5) Cultivate healthy and strong Chinese Cymbidium; do not apply excessive nitrogen fertilizer. More low-nitrogen, high-potassium organic plant growth promoters should be applied to enhance the disease resistance of the orchid plants. (6) Immediately cut off the diseased parts, carry out appropriate leaf treatment, and move them to a low-humidity location to prevent the spread of the Phytophthora pathogen. (7) Check the pH value of the medium at all times. When the pH value is lower than the critical point for Chinese Cymbidium growth, add plant ash or bitter soil lime to adjust the acid-base value to a moderate level. Soak bitter soil lime in water at a 1000-fold dilution for more than 12 hours, and irrigate an appropriate amount into the potting medium to adjust the pH value and inhibit the spread of the Phytophthora pathogen. (8) When it is found that an orchid plant is infected with the Phytophthora pathogen, immediately replace the medium and treat with chemicals right away for better results. Treating several days after planting or treating by soaking the plant makes it very difficult to achieve the expected prevention and control goal. Among the cultivation medium materials currently used for Chinese Cymbidium cultivation, some cultivation media often carry the Phytophthora pathogen. If the cultivation manager does not carry out appropriate treatment in advance or pile them for full fermentation before planting, the orchid plants are often very prone to disease. For the Rhizoctonia-type pathogen genus within the Phytophthora pathogens, it is generally very difficult to achieve therapeutic effects using chemical pesticides such as etridiazole or procymidone, which often troubles cultivation managers when managing Chinese Cymbidium cultivation. Therefore, one month before dividing Chinese Cymbidium, the cultivation manager should first thoroughly do a good job of environmental cleaning, spray the entire orchid room with chemical agents to reduce the number of pathogens, and after dividing and planting, irrigate the orchid plants and potting medium with etridiazole mixed with mepronil to inhibit the occurrence of pathogens. In normal times, the following can be used in rotation: (A) 25 percent etridiazole emulsifiable concentrate at 1500-fold; (b) 30 percent etridiazole wettable powder at 2500-fold; (c) metalaxyl wettable powder at 2000-fold; (d) 75 percent mepronil wettable powder at 1000-fold; Add spreading agent at 1500-fold to increase the effect. In summer, use in rotation once every 10-14 days; in winter, use in rotation once every 30 days. If Phytophthora disease has already been contracted, use 35 percent etridiazole wettable powder at 1500-fold mixed with 75 percent mepronil at 1000-fold, add spreading agent at 1500-fold, and spray the whole plant, including leaf surfaces, leaf undersides, bract leaves, stem base, medium, inside and outside of the pot, and other parts. Be sure to carry out disinfection work with the finest mist spray method to ensure the prevention and control effect. Try to maintain humidity and keep the whole plant dry within two days. Apply once every seven days until Phytophthora disease decreases. Among commercially available pesticides, there are many kinds of pesticides that have excellent results in preventing and controlling Phytophthora disease. However, Chinese Cymbidium plants are higher plants, and their tolerance to certain pesticide agents is relatively sensitive; after use, there will be some impact on the growth of Chinese Cymbidium. When some agents are mixed with other agents or chemical fertilizers, organic fertilizers, or even plant growth regulators and other products, it is very easy to produce phytotoxicity or growth disorders. When cultivation managers carry out disease prevention and control work, they need to be very careful when selecting agents and mixing them for use, so as not to cause serious damage to the orchid plants, which would make the loss outweigh the gain.