Since it first appeared in 2011, the emerging plant disease identified as Impatiens Downy Mildew (IDM) has caused quite a stir in the landscape and nursery industries throughout North America. If you have or are considering using Impatiens in your landscape or garden this year, read on!
Characteristic Symptoms of Impatiens Downy Mildew:
(On Impatiens) Leaves turn light yellow and curl downward, as if wilted
- Underside of leaves are coated in a white, fluffy growth that’s visible to the naked eye
- Flowers drop, shortly followed by leaves – only bare stems remain
- Young plants remain stunted
- Plant stems become water soaked (soft and mushy)
Disease and Management
If you discover that your impatiens have (or continually had) these symptoms since 2011, it may be that your plants were (or are) infected by Impatiens Downy Mildew, in which case there’s a few things you should know about the disease and it’s management:
- IDM infects all varieties and hybrids of the common garden impatiens (Impatiens walleriana)
- Caused by Plasmopara obducens . a water mold (Oomycota)
- Produces spores that can persist in the soil and cause infection for up to 10 years after the disease first appears
- Spores are spread via water splash (short distances), air currents (long distances), and mechanical contact (people)
- Disease thrives between 63-73 degrees Fahrenheit, meaning you may not see it at other temperatures even though it’s there
- Hot and dry conditions reduce symptom expression in infected plants
Presently, there are no effective treatments to suppress or eradicate infection once it occurs. Prevention is the best management practice, and can be accomplished through limited fungicide application (which as questionable effectiveness), careful watering practices that reduce moisture and humidity, and the use of alternative, non-susceptible shade plants such as coleus, begonia, and New Guinea impatiens (I. hawkerii). If you do happen to find plants that you think are infected with IDM, it’s recommended that you completely remove all potentially infected plant matter (fallen leaves, blossoms, and closet neighbors as well as root systems) to reduce the amount of infectious spores in the soil. Infected plant material should enver be composted, but rather burned or buried deeply to safely prevent further spread of the disease.
For more information on non-susceptible alternatives, we recommended that you visit this Michigan State University Floriculture Page: http://flor.hrt.msu.edu/IDM/mobileindex.htm
