A comprehensive review of common diseases in orchid cultivation
Main diseases of orchids:
① Anthracnose: The pathogen is Colletotrichum orchidearum, which mainly damages orchid leaves. The lesions are nearly round, with the center light brown or grayish white and the edges purple or dark brown. It mainly infects many orchids such as Cymbidium faberi, Cymbidium sinense, Cymbidium ensifolium, and Cymbidium goeringii.
The temperature suitable for pathogen growth is 22°C-28°C, with humidity above 95%, and the pathogen spores germinate and infect through wounds. Spraying water on leaves and watering easily worsen the disease; placing orchids too densely so that leaves overlap also easily spreads infection, and susceptibility differs among varieties. 'Datousu' among Cymbidium ensifolium and 'Dafugui' among Cymbidium goeringii are heavily susceptible; 'Tiegenglan' among Cymbidium and Cymbidium ensifolium is relatively resistant.
Control methods: Cut off diseased leaves and burn them promptly; avoid spraying water on leaves as much as possible and strengthen ventilation and light penetration; in the early stage of disease, spray 50% carbendazim or 50% thiophanate 500x-600x solution.
② Spot rot: For many orchids, this is an extremely serious disease. The disease starts from the base of the stem and then quickly spreads to the leaves and roots. ③ Black rot: This disease mainly occurs on Cattleya. It is mainly caused by water mold, and the disease is more severe in low-temperature and high-humidity environments. It first occurs at the roots and then spreads to the pseudobulbs and leaves, causing plant death. It is usually spread during repotting and division.
④ Cattleya leaf spot: This disease is very common and can be found in any greenhouse where Cattleya is cultivated. Usually small round black spots with clear boundaries appear at the leaf tips. When humidity is high, it causes leaf or pseudobulb rot. The disease can infect plants of genera such as Pholidota, Coelogyne, Cattleya, Paphiopedilum, and Laelia.
⑤ Bacterial soft rot: This is a disease of Cattleya and is extremely contagious. First, water-soaked dark green spots appear at the leaf tips, and then they expand. The pathogen enters through wounds, and it harms many cultivated plants. Susceptible orchids include some species in genera such as Cattleya, Phalaenopsis, Oncidium, Paphiopedilum, and Cymbidium.
Control methods for leaf spot, spot rot, black rot, and soft rot: First, do a good job of environmental sanitation in the orchid cultivation site, promptly clean up dead branches and fallen leaves, and eliminate and remove sources of pathogens. Strengthen management to promote robust plant growth and improve resistance. Strengthen ventilation and light penetration, appropriately lower air humidity, and minimize spraying water on leaves.
When diseased plants are found, immediately cut off the diseased leaves and destroy them. Disinfect the orchid cultivation environment, spraying disinfectant on benches, greenhouse paths, and even flower pots.
Spray antibacterial agents on orchid plants: 50% amobam 800x-1000x solution; 70% thiophanate-methyl 700x-800x solution; 50% wettable carbendazim powder 1000x solution.
⑥ Orchid viral diseases: Diseases caused by viruses are quite common and serious among orchids. Although no effective control method has been found so far, through years of research, the characteristics of the viruses and the patterns of occurrence and development of viral diseases have basically been grasped. On this basis, adopting some control measures to manage them is very effective.
Types of orchid viral diseases: So far, at least more than 7 viruses have been found and isolated and identified on cultivated orchids.
Cymbidium black spot: This is the earliest discovered viral disease. It can harm Cymbidium, Calanthe, Cattleya and its hybrids, Cymbidium, Paphiopedilum, Oncidium, Phalaenopsis, Vanda, and Epiphyllum. On the leaves of Cymbidium, jewel-like necrotic black spots are produced, but they are different from the anthracnose produced on Chinese orchids.
Cymbidium ringspot necrosis: It infects plants of genera such as Cymbidium, Cattleya, and Spathoglottis. On the leaves of Cymbidium, ring-shaped necrotic spots are produced.
Odontoglossum ringspot: This virus mainly infects genera such as Calanthe, Cattleya and its hybrids, Epidendrum, and Odontoglossum. On the leaves of Odontoglossum, ring-shaped necrotic spots are produced.
Cucumber mosaic virus disease: It mainly infects plants of the genera Dendrobium and Miltonia. On Dendrobium leaves, ring-shaped chlorotic spots are produced.
Control methods: Strictly select and plant virus-free seedlings and seed-grown seedlings; clear weeds in the garden on time and control pests; immediately pull out and destroy diseased plants when found; promptly disinfect tools and hands that have contacted diseased plants, and pots and potting materials that have been used for diseased plants must not be used again.
⑦ Orchid anthracnose: In the early stage of disease, round or semicircular reddish-brown patches first appear on the leaves, then turn dark brown, and yellow halos also appear around the lesions. In severe cases, the lesions merge into bands, the center turns grayish white and small black dots appear, causing the entire leaf to necrose, and the leaf base rots and falls off.
During the rainy season and greenhouse maintenance stage, if ventilation is poor, the potting soil is too wet, and sunlight cannot be seen for a long time, the disease is relatively severe. Never sprinkle water on the plant clusters, otherwise it will expand and spread. Some varieties have strong disease resistance, such as 'Tie Gansu' and 'Pulan' among Cymbidium ensifolium; Cymbidium sinense has moderate disease resistance; 'Yunfengsu' among Cymbidium ensifolium and 'Dafugui' among Cymbidium goeringii have weak disease resistance. In severely affected areas, in addition to cultivating resistant varieties, the pot spacing should be widened during both indoor and outdoor maintenance. After disease occurs, misting should be reduced, attention should be paid to ventilation, and at the same time spray 800x-1000x diluted carbendazim solution once every 3 days for 3-4 consecutive sprays, which can bring the disease under control. It is best to cut off severely diseased leaves and burn them.