Impatiens destroyed by Downy Mildew

I’ll admit it, impatiens were never at the top of my list of favorite garden plants. Everybody and anybody plants impatiens. Sure, they are cute and easy to grow, but I've always been drawn to the slow growing/bloom-for-only-a-few-weeks type of perennial.  Bottom line, they didn’t excite me. For the past eight years, I’ve lived in rental houses where I was forced to grow plants only in containers. I vowed that when I finally bought a house, I would not plant impatiens. Being a horticulturist, I knew there were other, more unique and intriguing plants out there that would thrive in the shady areas.

Impatiens walleriana

Nevertheless, after buying our first house this winter, I found myself drawn toward impatiens for my yard. I have come to realize there really is a place for this showy annual among the perennials and shrubs in one’s garden. A bland spot under the hedge in the front of my house needed a punch of color and within week, bam! the “Salsa Mix” Impatiens brightened it up. And then, after we removed a the  Juniper shrub from under the weeping cherry tree, I needed some quick color in there. A bunch of white impatiens did the job beautifully. 

Beautifully, that is, until one week ago...

At first, I thought something was eating the impatiens. In a large spot near the road, the plants were missing their flowers. But since the plants further back on the property still looked good, I thought it was a rabbit (further convinced after I saw a rabbit one morning just sitting innocently on my front lawn – a sight not common in my neighborhood!).  I bought some organic rabbit and deer spray to deter the creature and put down some fertilizer to encourage more blooms. But nothing worked. And then I received an email from a local nursery. It started with “Do you still have impatiens? Well, enjoy them while they last because Downy Mildew is destroying them across Long Island.” Not knowing what that was, I did some research and it turns out that Downy Mildew, Plasmopara obducens, is causing gardening (and growing!) havoc throughout various parts of the US this year. Symptoms include yellowing or stippling of the leaves, leaf margins curling downward, stunted growth, flower drop and white downy-like growth on the underside of leaves. The fungal disease can cause complete defoliation or plant collapse especially in landscape plantings under cool, moist conditions.

I realized my plants were not being eaten, they were being destroyed by this disease.

Downy-like fungal growth on the underside of the leaves

Downy mildew is a water mold. It likes and requires moisture to sporulate and cause new infections. Locations where the leaves stay wet for extended periods of time (either from dense plantings, overhead irrigation or excessive rainfall & humidity) are more susceptible. 

Read more about Downy Mildew here.

Apparently, regional outbreaks were common in 2011 and are spreading into 2012 due to spores over wintering in landscape beds. There is no control of Downy Mildew and it’s recommended that infected plants be removed immediately, placed into plastic bags and discarded. If fungal-laid leaves get into the soil, the spores may continue to live there for 3 years. So if you think you can just plant new impatiens next year, think again. A better bet would be to plant new guinea impatiens, coleus or begonias.

According to mainstreetnursery.com, it’s believed that because seed companies have been hybridizing impatiens to gain desired characteristics, the impatiens’ previous resistance to the disease has been bred away over time.

Yesterday, I sadly removed all my impatiens. Even the ones that looked good from above, had the tell-tale whiteness on the underside of the leaves. In their place, I planted some variegated coleus and white begonias with attractive brown foliage. I know it's late in the season (and frankly, it was slim pickings for me at the nursery!) but I do hope these will grow quickly enough and provide some color until frost. 

Turns out, I will miss my easy going impatiens after all, and hope to have them in my garden again one day. 

Sad state of affairs for these impatiens

What about you? Have you seen this problem in your area?


More about the impact of Downy Mildew on Impatiens walleriana:
http://www.greenhousegrower.com/article/26190/opinion-impatiens-put-to-the-test