Environmental Horticulture Providing useful, research-based horticultural information and opportunities to our readers!

December 24, 2013 – 09:39 am

Laura Sanagorski, Environmental Horticulture Extension Agent

Bill Schall, Commercial Horticulture Extension Agent

Downy mildew on impatiens is currently a concern in Palm Beach County. High humidity paired with cool nights created the perfect conditions for disease development. Downy mildews are caused by a variety of pathogens that tend to be specific to hosts; however Plasmopara obducens is the one that affects impatiens. Some literature indicates that downy mildew favors about 50 – 72 degrees Fahrenheit nighttime temperatures.

HOSTS - Downy mildew affects all hybrids and varieties of Impatiens walleriana, also called Busy Lizzy. New Guinea impatiens, Impatiens X hawkeri, is considered very tolerant. Counties adjacent to Palm Beach County have reported less severe outbreaks in 2011 and early 2012.

SYMPTOMS - Young plants and new growth are most susceptible and may show symptoms first. Initially, leaves may look a little yellowish or speckled. In fact, these symptoms look very similar to nutritional deficiencies. You may see faint gray lines on the tops of leaves or notice leaf edges curling downward. Sometimes the yellowing is not visible before leaf curling begins.

As the disease continues to progress, whitish downy looking growth will be visible on undersides of leaves. This whitish growth is spore-containing structures that have emerged from the lower leaf pores (stomata). Next, leaves and flowers will drop quickly, leaving mostly stems.

Source: palmbeachcountyextension.wordpress.com

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Other suggestions

My shade garden has the following:
-hostas (obviously not evergreen)
-impatiens (annual)
-lariope (good choice for you I think-- do a google search. It's a grasslike plant that spreads well and has spiky purple flowers in summer)
-pachysandra (good groundcover, grows to about 8 in tall, has little white flowers in spring, takes a couple years to really proliferate)
Good luck!

Oops - bought Miracle-Gro garden soil instead..

Of potting soil. The garden soil is for use in-ground only (not potting) and requires mixing it with the present garden soil (50-50 mix).
Unfortunately I live in a condominium and don't have access to any present garden soil.
I want to use the Miracle-Gro garden soil for potting if I can. Is there anything(s) I can buy to mix with it so I can do this?
Just potting up some vinca minor starts (dug with roots) and some annual flowers, such as impatiens and begonias.

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