Symptoms of Anthracnose in Orchids and Detailed Explanation of Prevention Methods
Orchids are also called Hu Ji Hua, the general term for the Orchidaceae family. The Orchidaceae family has a great many species, with approximately 28,000 accepted species at present. Orchid anthracnose harms many orchid flowers of the genus Cymbidium, and the disease is severe when plants are maintained in greenhouses, sometimes causing entire leaves to wither and die.
1. Symptoms
In the early stage, circular or semicircular reddish-brown spots appear, which later gradually turn dark brown. The outer edges of the lesions mostly have a yellow halo. In severe cases, many lesions gather together, forming wavy or striped dark brown lesions. In the later stage, the center of the lesion turns grayish-white, with many small black dots borne on it. The disease occurs most frequently on the middle and upper parts of the leaves.
2. Occurrence Characteristics
The disease is severe during the rainy season and in greenhouses. The pathogen overwinters in the tissues of diseased leaves. When water is frequently sprinkled on the leaf surface or when leaves overlap one another, the lesions easily expand and spread. The resistance of orchids to this disease varies by variety. For example, 'Da Feng Su' among Cymbidium ensifolium and 'Da Fu Gui' among Cymbidium goeringii have weak disease resistance, while 'Tie Gan Suo' and 'Pu Lan' among Cymbidium ensifolium have strong disease resistance, and Cymbidium sinense has moderate disease resistance.
3. Prevention and Control Methods
When watering, never pour water onto the leaves. On the premise of ensuring air humidity, provide appropriate ventilation and light, and widen the spacing between pots when placing them to prevent infection. In severely affected areas, pay attention to cultivating disease-resistant varieties. Promptly prune diseased leaves and burn them. After the disease occurs, spray with 500 times diluted carbendazim solution, once every 7 days, for three to four sprayings in total, with good results.