Clean plants should be obtained from suppliers and seedlings may be drenched with fungicide before planting. Rotation away from impatiens for three years may be successful in garden beds. The pathogen may overwinter in Delaware, especially in a greenhouse or sheltered location. There are some new resistant impatiens hybrids such as ‘Bounce’.Īffected plants should be removed from garden beds or pots and be discarded in the trash, not composted nearby. There are similar downy mildews on coleus and on Asteraceae, but they not caused by the same pathogen and will not cross infect. capensis, may become infected but not sporulate. The pathogen has not been found to infect I. There is no harmful effect to humans from contact with the downy mildew pathogen.ĭowny mildew caused by Plasmopara obducens affects all Impatiens walleriana hybrids, but does not affect New Guinea impatiens. The pathogen is favored by wet, humid conditions, typical of the coastal climate found in Delaware. The disease on impatiens is an aggressive disease and has been confirmed in most Eastern states, as well as California and a number of mid-western states. Oospores are thick-walled resistant spores and are suspected to overwinter.ĭowny mildew diseases are very host specific. Later in the infection process, oospores may be formed in the stems and roots of infected plants. Sporangia are spread by air currents, by water splash, and on infected leaf material and seeds. Impatiens downy mildew sporangia are produced in abundance and can be seen as white patches on the lower leaf surface of what is normally a smooth surface (not hairy). Sporulation (production of sporangia) of the downy mildew pathogen occurs on the undersides of the leaves. Chlorosis (yellowing) is followed by leaf drop, stunting and overall poor condition of plants. The earliest symptom on affected plants is yellowing on the top leaf surface, often accompanied by a downward curling of leaves. It was confirmed on garden balsam, Impatiens balsamina in New Castle County in June 2012. Downy mildew was first confirmed in Delaware on Impatiens walleriana in Kent County in August 2012. Originally found in Europe, impatiens downy mildew was detected in greenhouses in California in the U.S. Downy mildew of impatiens is a serious disease in the United States, caused by the fungus-like Oomycete, Plasmopara obducens.
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