First report of Pythium root rot of chrysanthemum in Vietnam and control with metalaxyl drench

This is the first report of Pythium root rot of chrysanthemum, and the pathogen responsible, Pythium aphanidermatum, from Quang Nam and TT Hue Provinces in Vietnam. The typical symptoms included stunting, wilting, and necrosis of the main, lateral and feeder rootlets. A black necrotic lesion girdling the lower stem was present in some diseased plants. The root rot commonly caused death of diseased plants and affected plants at all growth stages. The pathogen was also isolated from transplants affected by root rot, and sampled directly from boxes transported from Dalat, Lam Dong Province, the source of most transplants used in Quang Nam. Metalaxyl was shown to provide effective control of Pythium root rot in a field trial when used to dip transplants before planting, and as a regular drench. Metalaxyl also provided effective control of the disease in commercial crops on the farm where the field was located. © Australasian Plant Pathology ociety 2010.