Features

• A fungal-like pathogen called Plasmopara obducens causes downy mildew infections in impatiens. The disease requires humidity levels of 85 percent or higher and wet leaves to create infections in plants. It is the most problematic in fall and spring when the daytime temperatures are fairly warm and the nights are still cool, according to A.R. Chase from Chase Research Gardens.
  
  

Effects

• Downy mildew infections are characterized by a grayish-white fungal growth on the undersides of leaves. Mary Hausbeck from Michigan State University notes that, since most plant owners are not usually in the habit of looking on the undersides of leaves, the infection often goes unnoticed until the disease is well established. Other symptoms include leaf distortion, plant yellowing and stunted growth. The rate of plant death is high among seedlings and young plants.
  
  

Prevention/Solution

• Discard or destroy infected impatiens plants and healthy impatiens that are close to the diseased plants. Treat all remaining impatiens with fungicides to prevent infection from occurring. The disease does not spread to plants outside the impatiens species.