What are the Causes and Symptoms?
The impatiens fungus is caused by the pathogen Plasmopara obducens, which is very difficult to control. The fungus on impatiens plants forms in cool moist or humid conditions, generally in spring or fall. Ornamental impatiens and downy mildew go hand in hand in 30 states of the Union with only a few resistant varieties available. It affects both cultivated and wild impatiens, but not New Guinea impatiens. Downy mildew starts on the underside of the leaves and causes them to fade and develop stippling much like that seen with heavy spider mite feeding. The leaves get droopy and eventually white cottony spores will appear on the foliage. Eventually, all the leaves drop off and you have a skeleton of a plant. Without leaves, the plant can no longer feed itself with carbohydrates harvested through photosynthesis and it will wither and die. Any fungus on impatiens plants is contagious to other plants in the group but it does not affect any other ornamental species.
What to Do About Impatiens and Downy Mildew?
The impatiens fungus is actually not a fungus, but mildew, and as such doesn’t respond to fungicides. There are applications that work as a pre-emergence but once the plant has the disease, there is nothing to be done except remove it from the garden. The mold is already in the soil by that point, and it is, therefore, unwise to plant impatiens again since the pathogen can overwinter and lurk until its preferred host is in range. Using plant alternatives for impatiens downy mildew is the best choice to prevent dying plants. There are many shade ornamentals that are suitable alternatives to planting impatiens.
Plant Alternatives for Impatiens Downy Mildew Prevention
Many shade ornamentals can provide the color and interest of impatiens without the danger of the mildew. Below are just a handful to choose from:
Joseph’s Coat comes in many hues and has notable foliage. Coleuses are also spectacular colorful leaved plants in tones from green to pink and yellow, plus many more in between. Fuchsia, begonias, and lobelias are all easy to find in nurseries with vast form and texture available. Elephant ears, Alocasia, and Oxalis are interesting and impactful foliage plants for shade. Scarlet sage and mealycup sage are forms of salvia and add dimension as well as color.
There are many more alternatives to planting impatiens that will provide the color and drama you require in your shade garden.
