Impatiens Downy Mildew
Impatiens downy mildew is a mold that affects impatiens (Impatiens walleriana), I. balsamina, and native jewelweeds (I. pallida and I. capensis). Lower leaves of infected plants turn yellow or stippled, begin to curl, and eventually drop off. A sure sign that it is downy mildew is the development of a white powdery growth on the underside of the leaves.
The disease can be contracted through contact with infected plants or soil, or through wind-dispersed spores. There is no successful treatment for plants once they have the disease, and the disease can remain in the soil for years. Once an area is infected, it’s recommended to remove all impatiens from the area, including roots, and throw it in the trash in a plastic bag; do not compost. Avoid planting impatiens there for several years, instead using alternative shade plants such as New Guinea impatiens (I. hawkerii), begonias, coleus, iresine, torenia, or other bedding plants, which would not be affected.
For more information on impatiens downy mildew from the UW Extension, click here.