Chlorothalonil is a commonly used fungicide for controlling orchid diseases.

The pure compound is a white crystalline solid, odorless and tasteless; the technical-grade product has a slight irritating odor. It is insoluble in water, slightly soluble in organic solvents, relatively stable at room temperature, resistant to rain washing but not to strong alkalis. It has low toxicity to humans and livestock. There are two formulations: 75% wettable powder and 4% dust. Its chemical name is 2,4,5,6-tetrachloro-1,3-dicyanobenzene. Chlorothalonil is a broad-spectrum fungicide with both protective and curative action, with stable efficacy and a long residual period. The concentration used is generally a 600- to 800-fold dilution of wettable powder spray; for dusting at the seedling stage, 1.5-2 kg of dust per mu (667 sq m). It can controlorchidleaf blight,orchidanthracnose,orchidring spot, as well as fungal diseases of chrysanthemum, rose, Chinese rose and many other flowers. Precautions when using: (1) Do not use too high a concentration, as too high a concentration will cause phytotoxicity to the plants; (2) Do not mix with lime sulfur; (3) This agent can cause skin allergy in people, so take care to protect the skin. (Liu Zhongjian)