Concern surrounding Impatiens Downy Mildew (IDM) was palpable at the OFA Short Course in mid-July. Conversations with greenhouse growers regarding current challenges, frequently turned to discussions regarding how cope with IDM. There were some important takeaways from those conversations and useful information that should be shared with customers if and when the topic of IDM comes up.
- Despite the broad brush the name “Impatiens Downy Mildew” suggests, of the cultivated species, only Impatiens walleriana (the common garden species) and its hybrid varieties are susceptible.
- New Guinea Impatiens (Impatiens hawkeri) is resistant and, if necessary, can be used in rotation with susceptible impatiens in planting beds. Without a susceptible host the pathogen will eventually die off in the planting bed and I. walleriana can be safely planted again.
- The disease can be recognized pretty easily (click here for images of symptoms) and if acted upon quickly, the overwintering capacity of the pathogen can be significantly limited (click here for recommended practices).
- Michigan State University and Cornell University, in collaboration with plant pathologists in industry, have developed fungicide protocols to be used in the prevention and management of Impatiens Downy Mildew. (click here for protocols).
If left to its devices and under appropriate environmental conditions, Impatiens Downy Mildew can wipe out a bed of Impatiens walleriana
with a vengeance, causing all leaves and flower petals to drop off. However, if you buy from a reputable grower, take some preventative measures, and are careful to watch out for the signs and symptoms of the disease there’s every reason to believe that the common garden impatiens will continue to be a mainstay of our landscapes.
Additional resources are available at the American Floral Endowment (AFE) website