Thursday, September 27, 2012

Impatiens blight disease -- Trouble in the landscape

impatiens blight disease 2013
Impatiens blight disease will likely continue in 2017
Downy mildew has arrived in the Mitten.  Impatiens blight disease.  Don't be fooled by the soft moniker--this ornamental flower killer means business.  "It is likely that impatiens could lose their place in our landscapes if they cannot be grown reliably."  This quote from the esteemed Michigan State Extension Service causes icy fingers to clamp around the heart of gardeners who've relied for decades on these colorful and easy plants to provide tone  and warmth to the shade garden. 

impatiens fungus 2013
Impatiens fungus or blight hit hard in 2012 and is full blown in 2013.  First the plants appeared sickly.  Then the blooms fell off, leaving translucent stems pointed upward like outstretched fingers from an open hand.  Those disappeared, leaving only a puzzled memory of last year's hearty fall blooms.  Chalking it up to a chilly spring followed by the hottest July in recorded US history, there was only passing concern.  When the stalwarts in the windowbox began to fade the circumstances became troublesome.  All those lovely flats painstakingly planted-- for naught.  Will this happen again?

At a Sunday baby shower hushed whispers about an "airborne" disease triggered alarm.  Is this blight insidious or an aberation?  Are there measures to prevent the future spread of disease for next season?

Look for pale white spots on the underside of leaves.  Remove the leaves and destroy.  There are commercial fungicides available from growers.  Copper based fungicides would be more attractive to naturalists.  Once a plant is infected, it's too late for the fungicide.  Organic gardeners should rely on prevention and early intervention:
  1.  Lift the leaves before you buy.  The disease begins at the greenhouse.
  2. Avoid overhead watering, irrigate the plants with watering cans or hoses directed at the base.
  3. Chose a site with good drainage, medium early sun access and low humidity.
  4. Use adequate but not excessive fertility.
  5. Monitor the plants frequently, removing diseases leaves.
  6. Clean tools frequently.
  7. Remove infected plants and try to avoid spreading by touch.
Impatiens are officially off the "low maintenance" list.  At least they weren't a cash crop. 

A safe bet?  New Guinea impatiens are resistant to downy mildew. 

A new introduction, Sunpatiens are designed to thrive in sunny areas and seem exempt from the disease.  These planted in a warm front bed amongst lavender and cleome were slow to take, but have bloomed heartily in September. 

But will so miss those bloomin' bizzy lizzies!

Related Articles:

Mycorrhizza -- Fun with Fungi in the Garden

Turtlehead and Other Fall Blooming Flowers

When Should I Plant Annuals in Southeast Michigan?