Cases of Downy Mildew on Michigan Impatiens has been confirmed. The confirmation came from findings on greenhouse bedding and double impatiens. Downy Mildew can be spread by wind-dispersed aerial spores from infected plants or introduced into a greenhouse by infected materials such as plants, cuttings or plugs.
In many cases the Downy Mildew appears to form overnight as the very early stages are microscopic, this allows the pathogen to advance unnoticed until it explodes with its white mildew. The plants can appear fine from the top as the mold forms on the undersides of the impatiens leaves (as seen in the photo on the right).
- Stippling of leaves or light-green yellowing
- Subtle grey markings on the upper leaf surface
- Downward curling of infected leaves.
- White mildew on the undersides of leaves.
- Stunted growth of the plants overall structure
- Flower and leaf drop, which results in bare leafless stems
- Infected stems become soft, causing the plant to collapse under continuous wet and cool conditions
Once downy mildew has been discovered the infected plant should be destroyed and removed from the area immediately.
If you are looking to purchase impatiens ask your retailer if they have had any problems with impatiens this year. While plants may appear healthy in stores they can become infected once planted into your landscape, which could cause problems for other plants in your yard.