Impatiens Downy Mildew
Impatiens Downy Mildew (IDM) has recently become a serious problem for many gardeners who grow impatiens. There are several strategies that can be used to control IDM.
Impatiens are a popular choice for the shady garden, but there is a disease (Impatiens Downy Mildew) that has started to pop up around the Midwest that we need to keep an eye on. This isn’t a new disease and has been found sporadically around the U.S. since the 1940’s. It has been positively identified in Wisconsin recently, along with Indiana, Illinois, and Michigan in past years. This shouldn’t stop you from planting them though because you may not have any problems at all. I just want you to be aware of it. You should also know that it only attacks the regular garden variety Impatiens and not other varieties like New Guineas. It was also more prevalent in actual landscape plantings, and less in containerized plants that use sterilized soil mixes. Let’s take a look at the symptoms so you know what to look for, and some cultural practices that you can use to help avoid it all together.
So, what are the symptoms? Although the most distinguishing feature is grayish fuzz on the underside of the leaves, most gardeners won’t notice this first. Look first for yellowing of the leaves. Leaves could also be curled downward or distorted. Stunted plants or those that drop their flower buds early are also candidates. If you see any of these, check the underside for the fuzz. If it’s there, your plants could be infected. Now, I also want to say don’t jump to conclusions because other factors can cause these symptoms, and if your fuzz is a different color, it could be another disease altogether. Bring a sample to your Extension office or local garden center to be positive.
What should be done if plants are infected? If it’s determined the disease is present, the best thing to do is pull the plants and dispose of them. Don’t stop there though, contact your Extension office and let them know. They may even want you to send them the plant. Do not compost the plants.
Now, more importantly, what can we do to help? Use proper watering techniques. The disease spreads more rapidly in wet, cool conditions. If you need to water, water in the morning so the excess moisture can evaporate. Give your plants a little extra spacing to allow for better air flow as well. Also, use an all-purpose fungicide as a preventative measure. Most fungicides are designed to work preventively so don’t wait until you start seeing symptoms if you want to be on the safe side.
As gardeners, we need to be alert at all times for the potential of disease and insects, and every year, there always seems to be something new out there.