The varieties susceptible to impatiens downy mildew are mainly impatiens walleriana , but also I. balsamina, I. pallida, I. capensis and I. glandulifera and any I. walleriana interspecific hybrid like Fusion© impatiens.
This particular strain of downy mildew is a parasite that must have only one host plant and can’t move to other bedding plants like tomatoes and phlox. It also doesn’t transfer to New Guinea impatiens hawkeri, Ganfare and the interspecific hybrid SunPatiens© impatiens. It is believed the impatiens downy mildew isn’t dangerous to humans.
A little history of this impatiens mess: It was first reported back in 1942 but this epidemic first showed up in the United Kingdom in 2003, seen in a few US greenhouses in 2004 and became established in the northeast by 2009. By 2011 it was in ten NE states and by the summer of 2012 was in 35 states. Currently it ranges from Canada to Florida and west into northern Illinois. The University of Illinois reported their walleriana crop infected in 2011. As of spring 2013, it’s unknown how it will affect downstate Illinois.
Once it gets going, it will go through an entire community through and takes up to 3-5 years to finally get out of the soil if no new plants with this mildew are introduced.
|New Guinea impatiens hawkeri|
Basically, the disease will look like a white soft covering on the bottom of the impatiens leaves. As it works, the leaves and flowers will wither, die, and drop from the plant. Quickly the entire plant will die. Growers are finding it extremely difficult to keep plants disease free long enough to get them to the retail nurseries and stores. To do so, they are using massive amounts of chemicals that may not be effective once they’re in your garden.
Once you have infected plants in your garden there is nothing you can do to save the plant. You are not licensed to use the chemicals used in nurseries. Pull all infected plants, remove with any dropped debris and destroy (do not compost.) It is spread by the wind, water, plant material and by lying dormant in the soil until you plant impatiens walleriana again. Right now it’s not known if ground freeze will eliminate the disease. It does not spread by seed.
Most greenhouses in affected areas are only selling the walleriana variety in hanging baskets hoping it will not have the spores in the soil. Some have stopped selling altogether and are offering alternative suggestions.
|Photo from Ball Hort. Center|
impatiens Super Elfins
Has it moved into Illinois? If you go to a reputable local greenhouse/nursery, ask them about this problem and their plants. No nursery owner wants to sell you infected plants and their honesty is part of good business. What you may find is the problem is already in your soil from plants bought through the big box stores last year. Not that big box stores are bad, but they may buy the infected stock from nurseries out east (often Florida) and spread the disease unwittingly.
If you do buy impatiens walleriana, realize they may not last the entire summer. This is especially true if you plant them in an area where they prematurely died last year. Face it, one of the reasons we love this variety is because it blooms almost carefree from June to the first frost. And for the beautiful subtle colors not found in the other impatiens varieties. Plus, it blooms in full shade better than mildew resistant varieties.
What to plant if you decide to skip impatiens until this garden fungus is under control from the suppliers? Most greenhouses, nurseries and retail plant stores have a nice selection of shade loving plants. Some of the obvious are Begonia (although more expensive than impatiens) and coleus. Coleus has made a huge leap to crazy beautiful in the last few years. The new hybrids are in many colors, designs and sizes.
Impatiens walleriana was a huge cash crop for the floral industry and this infestation will severely hurt the business. Do you stop planting in the shade? Heck No! Check out something new and experiment with something you’ve never tried before. Think of this as an opportunity to break out of the impatiens rut and experiment with the new.