What You Need to Know About Impatiens Downy Mildew
By Sarah Mooney
Impatiens walleriana are flowers that my mother and grandmother have always planted in their gardens, and I was attracted by their summer-long color and affordable price so I picked some up during my trip to a local garden center. After I checked out, I looked at my receipt and noticed a warning about downy mildew infecting Impatiens walleriana. I became curious and decided to find out more.
What is Impatiens Downy Mildew?
Last summer, in many states, Impatiens were killed by downy mildew (caused by Plasmopara obducens). Downy mildew is a pathogen that is spread through air and water, and can stay in the soil for years, making it unwise to replant impatiens in the same beds.
Contracting Downy Mildew
If your impatiens are damp for long periods of time, they will be more susceptible to contracting the mildew. Other contributing factors are the weather as well as the density of your planting. Impatiens that are numerous and close together are likely to spread the mildew to one another, and closely planted impatiens may take longer to dry off after a watering due to less overall air exposure. Cooler temperatures also promote the growth of this mildew.
The number of states impacted by Impatiens Downy Mildew increased significantly from the year 2011 to 2012. A map at http://www.todaysgardencenter.com provides a visual of the spread.
How to Identify Downy Mildew on Impatiens
1. Your impatiens will begin to appear as though they need water; they may droop.
2. There may be a white or gray fuzzy coating on the underside of the leaves.
3. Leaves may begin yellowing.
4. Blooms will begin to thin, and eventually stop.
5. Leaves and flowers will be depleted from plant.
How to Handle Downy Mildew
Unfortunately, if your impatiens have Downy Mildew, this is their end. It is important to carefully dispose of your impatiens when you remove them from your flower beds, which you will want to do if they are infected.
Do not put infected impatiens in a compost pile or in any area where they will rot among other plant life. This can increase the chances that it will spread. Instead, you can put your impatiens into a garbage bag or even burn them.
Impatiens that are not showing signs of Downy Mildew but are near impatiens that are infected will need to be removed also. Once your plants are infected, the soil that the impatiens are in will be able to spread the mildew to newly planted impatiens. Because of this, you will not want to plant impatiens in beds that have had infected flowers in them in the previous season. You may even want to wait a few years before you consider planting impatiens in a once infected area. Fortunately, you can still plant in this area. Pansies, begonias, and violas are some examples of flowers will all bloom in the same shady environment as impatiens, but will not contract downy mildew.
There are different opinions about treating the bed with fungicide as a preventative measure. It is recommended that fungicide is used by a professional, and that you do not try to treat the mildew with a fungicide because it will be ineffective. It is suggested that if fungicide is applied, it is done at the beginning of the season rather than the end.
There is hope for people who have dealt with downy mildew on their impatiens, because breeders are working to develop resistant impatiens that are not susceptible. If my impatiens get infected, I will keep my eye out for these new breeds in the coming seasons and explore other options for my shady garden beds.
Sarah is new to gardening and eager to share her discoveries in hopes of clarifying the process for fellow beginners. Her other hobbies include making art, baking and exercising when she isn't busy studying for her Master's Degree in Social Work.