Do you plant impatiens every year in your garden or containers? Well this year (2013) you might want to consider something else. Downy Mildew is currently wiping out plantings of this popular annual and even causing growers to stop growing them. I have filled many benches with flats and flats of these annuals and spent much time colour blocking them on those benches. They have always been a hot seller. But this disease has shown no sign of stopping and it will really show at your local nursery this season.
Downy Mildew is a pathogen called Plasmopara obducens and only affects Impatiens walleriana and Impatiens balsamina. It does not infect New Guinea impatiens. It produces a white fluffy coating on the underside of the leaves but does not show it for 5-14 days. The plants will continue to deteriorate. There are no resistant varieties and fungicides have proven to be ineffective. And another important factor is that the fungus remains dormant in the soil and can even live there for up to 5 years. So going back to planting impatiens in a few years will cause the fungus to re-emerge.