Orchid anthracnose is a prevalent and serious disease affecting orchid cultivation, especially in South China. It not only impacts orchids but also other ornamental plants such as poinsettia, jasmine, privet, bergamot, and hibiscus. The disease can significantly reduce the aesthetic value of the plants and lead to severe economic losses for growers.
The symptoms of orchid anthracnose typically begin with small reddish-brown spots on the leaves. Over time, these spots expand into larger, grayish to pale white lesions. The affected areas on the leaves may appear as semi-circular, round, elliptical, rhombic, or irregular shapes, ranging from 0.5 to 1.2 cm in length and 0.3 to 0.5 cm in width. As the disease progresses, the lesions may merge into large patches or cause the leaf tips to wither. The central part of the lesions often turns dark brown or gray, and some may have a yellow-green halo around them. In the later stages, small black specks (spores) appear on the surface of the lesions, which can easily rupture, leading to yellowing and eventual death of the leaves.
The pathogen responsible for this disease is a fungus, specifically *Mycoplasma* species. These pathogens survive in infected plant debris and soil during winter. In the following season, they produce conidiospores that infect orchids through stomata and wounds, especially after rain or when insects are active. The ideal conditions for spore germination are temperatures between 20–25°C and humidity above 80%. In Guangzhou, where winters are mild, the disease can occur when environmental conditions are favorable, particularly during the hot, rainy months of May to June, or in September to October. High humidity, sunny weather, and frequent rainfall, along with poor management practices such as overwatering, overcrowded planting, leaf damage, and poor drainage, can all contribute to the spread of the disease. In northern greenhouses or home-grown orchids, the disease can occur year-round if conditions are not properly managed.
To control orchid anthracnose, several measures should be taken. First, proper orchid care is essential. Avoid overcrowding, protect plants from frost, and handle them carefully to prevent damage. Use appropriate pots, avoid excessive watering, and ensure good air circulation and lighting. Apply balanced fertilizers with increased phosphorus and potassium to improve plant resistance.
Second, remove infected leaves promptly, and burn them to eliminate the source of infection. Afterward, apply a 0.5% to 1% Bordeaux mixture to the ground and pots, repeating this treatment 1–2 times.
Third, chemical control is necessary at the early stage of the disease. Spraying 50% Mancozeb WP diluted at 500 times or 30% Thiophanate-methyl WP at 2000 times can be effective. Repeat the application every 10 days for 3–4 times. During the active phase, use 50% Carbendazim wettable powder at 800 times, 50% Mixed Sulfur Suspension at 700 times, 25% Triadimefon at 1000–1500 times, 50% Benomyl wettable powder at 1000 times, or a combination of 69% Metalaxyl + 75% Chlorothalonil (1:1) at 1000–1500 times. Other options include 65% Polyram wettable powder at 800 times, 75% Chlorothalonil + 70% Thiram at 800–1000 times, or 25% Triforine at 500 times. Spray every 7–10 days, alternating products for 3–4 applications to achieve optimal results.
Finally, regular preventive spraying is recommended to protect new growth. Options include 1% Bordeaux mixture, 75% Chlorothalonil + 70% Thiophanate (1:1) at 800 times, 80% Mancozeb at 600 times, 50% Benomyl at 800 times, or 20% Tricyclazole at 800 times. Apply once every 7–10 days for 3–4 consecutive sprays to maintain good disease control.
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