|Underside of leaf|
Initially, leaves may look yellowish or speckled. As the disease progresses, whitish downy growth, which is the spores that spread the disease, will be visible on the undersides of leaves. Chemical treatments such as Ortho Max Garden Disease Control can be applied to prevent the disease but are not effective for plants that already have it. Remove infected plants and bag them. Check impatiens before buying. Don't buy any that have a powder-like substance on the leaves' undersides.
Downy Mildew attacks Impatiens walleriana, the most common species. SunPatiens and New Guinea impatiens are not susceptible. Also consider planting other flowering plants such as begonias, lobelia and osteospermum.