Detailed Explanation of Disease Prevention and Control Methods and Technical Key Points

Symptoms: In Taiwan, China, they occur in allfour seasonsthroughout the year, but the disease is most severe during the plum rain season, under conditions of overwatering or poor ventilation, and seedlings that have just been removed from flasks are especially vulnerable. The symptoms vary among different orchid genera. On Cattleya, Phalaenopsis, Dendrobium, Oncidium, and Rhynchostylis, brown lesions appear on infected parts, expanding rapidly under high temperature and high humidity into large brown patches that eventually turn dark brown, leading to leaf drop, stem rot, and death of the entire plant. The roots are also attacked and rot, spreading to the pseudobulbs or above-ground parts. If large-floweredCymbidium(tiger orchid, East Asian orchid) and Chinese orchid varieties are infected, they show yellowing but do not developsoft rotdisease. Prevention and control methods: 1. Avoid overwatering or excessively high air humidity; improve ventilation and ensure adequate light. 2. Avoid excessive use of nitrogen fertilizer to reduce leggy and weak growth. 3. Immediately remove diseased plants or excise diseased tissue at the early stage of infection. Soak the uninfected parts along with their growing medium and pots in a 300-fold copper sulfate solution or a 600-fold 75% chlorothalonil wettable powder solution for 10 minutes for disinfection. The next day, spray with the same chemicals for prevention. 4. Apply 70% mancozeb wettable powder to the cut wounds of diseased plants, then place them in a dry location and do not water for 1 week; this can curb the spread of the disease. 5. Sterilize the knives used to cut diseased plants to prevent transmission. 6. Therapeutic chemicals: 1000-fold Previcur (propamocarb hydrochloride) solution or 500-fold 50% phosethyl-Al solution; spray seedlings once a week and mature plants once a month. 7. For routine prevention, use 1:1:200 Bordeaux mixture or 500-fold 70% mancozeb solution, spraying regularly once every 2 weeks. During the rainy season, switch to once a week. (Xue Congxian)