by Dr. Stephen Nameth
Department of Plant Pathology
Powdery mildew is one of the most wide spread diseases in the floriculture production industry. In most cases, symptoms of this disease are relatively easy to identify. The disease is characterized by the fluffy, white fungal growth on the leaves, stems, and flowers of infected plants. The disease typically shows up on leaves first and if left unchecked it will spread to the stems and flowers.
This disease is responsible for economic losses in greenhouse roses, Gerbera Daisy, Zinnia, perennial phlox, just to name a few. Within the last few years it has been a problem on Poinsettia. As mentioned, the host range of the powdery mildew fungi is quite large, yet each individual mildew fungus is specific for the host it infects. Rose powdery mildew will not infect Gerbera, and Gerbera will not infect Zinnia, and so on. In the greenhouse, powdery mildew tends to be more of a problem later in the growing season when the nights temperatures get cooler. However, it depends on the individual organism as to when and where it will show up.
Controls for this disease include, allowing for plenty of air flow around plant material and avoiding overhead watering late in the day. In severe cases chemical control may be warranted. Chemicals labeled for greenhouse use are thiophanate-methyl, triforine, and propiconizole.
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