If impatiens will be making an appearance in your garden beds or containers this growing season, you should be on the alert for downy mildew disease. The eastern part of the United States has reported serious problems with downy mildew infestations on impatiens plants.
The problem can develop in large greenhouses where bedding plants are grown, and can appear on seemingly healthy plants in the garden if they were infected when you bought them, or you plant them in an area where there was downy mildew last year.
Most impatiens plants can fall prey to this disease, but New Guinea hybrids — the types with really large flowers — seem not to be susceptible.
At this point, the best advice is to check plants carefully before buying them. Examine the undersides of the leaves to make sure there’s no white, fuzzy growth — the first sign that the plant is infected.
When planting impatiens, space them far enough apart in the garden that they dry readily — moisture and high humidity promote development and spread of this disease.
If your impatiens begin to show symptoms, remove and trash them immediately, then keep a close watch on any remaining plants. Avoidance and removal are the only practical methods of combatting this disease, should it show up in your garden.