Symptoms and Control Methods of Fusarium Wilt

This disease affects the roots of Cattleya, Oncidium, Dendrobium and Cymbidiumorchidsand other species, and its pathogen is Fusarium oxysporum f. sp. cattleyae (Fusarium oxysporum). The pathogen invades the plant through the roots or enters through the cut surfaces of newly divided plants. In severe cases, diseased plants die within 3 to 9 weeks after infection; under normal circumstances, diseased plants may remain in a weakened state and continue to survive for more than 1 year. In such cases, the symptoms on the aboveground parts of the diseased plant are similar to those caused by Rhizoctonia solani root rot, namely yellowing and twisting of the leaves and thin, weak pseudobulbs. Both diseases lead to extreme rot. The diagnostic symptom of Fusarium wilt is the appearance of band-like or ring-like purple lesions on the epidermis and subepidermis of the rhizome, with the vascular bundles also showing a pale pink-purple color, and finally the entire rhizome is affected and turns purple. As the disease progresses, the rot extends into the pseudobulbs. For its control, remove and destroy all diseased parts, and transfer the plant into a pot filled with fresh medium. Benlate 50% wettable powder is very effective in controlling this disease. Prepare the chemical as an aqueous solution and soak the diseased plant for 5 minutes or apply it as a drench, using a concentration of a 1000-fold dilution. If necessary, repeat the application once within two weeks. (Liu Zhongjian)