Discussions of Impatiens Downy Mildew are still burgeoning in the horticulture world. The disease is not new, having been in the US since at least 1897 when it was reported on wild species of impatiens. The disease has been more prevalent in the last ten years and was significant in some landscape plantings in the US in the last two years. However, prudent measures will allow this beautiful plant to continue to be a valuable part of our crop mix.
The causal agent of impatiens downy mildew affecting crops is Plasmopara obducens, a "water mold" or oomycete. This pathogen only infects some species within the genus Impatiens and cannot threaten other flower crops. Impatiens walleriana (common garden impatiens) are affected by impatiens downy mildew but New Guinea impatiens (I. hawkeri) are highly tolerant of this disease.
Symptoms
Impatiens infected with downy mildew can simply appear non-vigorous with yellowish or pale green foliage and mild, inconspicuous mottling. These subtle symptoms can be missed or mistaken for other problems. As the disease progresses, advanced symptoms may include stunting of plant growth, downward curling or distortion of the leaves, loss of leaves, wilting and plant collapse.
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