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Downy mildew on impatiens identified in Georgia retail nursery and landscape

Dr. Jean Williams-Woodward- University of Georgia Plant Pathologist
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Downy mildew on impatiens identified in Georgia retail nursery and landscape
Downy mildew on impatiens (Impatiens walleriana), caused by Plasmopara obducens, has been confirmed from a commercial nursery and a home landscape sample this week. The commercial sample, submitted by the Georgia Department of Agriculture, originated from a retail nursery in the Atlanta area. The home landscape sample is interesting in that new impatiens plants were not transplanted into the landscape bed this year and that the impatiens are allowed to reseed each year. This could mean that the pathogen has survived within the landscape bed from infected plants in previous years. It is not known whether impatiens downy mildew can survive within seed. This bed is located in a shady area and is irrigated with spray emitters that wets the foliage regularly, which creates an ideal condition to spread the disease to adjacent plants. Furthermore, the cooler, wet weather that northern Georgia has seen over the past few weeks has likely contributed to disease development and spread. At this time, we don’t know how widespread impatiens downy mildew is within the state. It is also likely that hotter and drier weather patterns usually seen through the summer will stop or slow disease development.
Downy mildew symptoms on infected plants begins with leaf stippling, downward curling of leaves, leaf yellowing, and leaf drop and disintegration leaving the stems bare. The downy mildew pathogen sporulates profusely on the backside of the leaf, as well as from infected stems as they soften and collapse. If you suspect downy mildew on impatiens within Georgia, please submit a sample to confirm its presence to the UGA Department of Plant Pathology Plant Disease Clinic in Athens. The form and address can be found here:http://plantpath.caes.uga.edu/extension/documents/PlantDiseaseSubmissionFormApril2012.pdf. For more information, contact Jean Williams-Woodward at jwoodwar@uga.edu.