Posts tagged ‘Impatiens Downy Mildew’

April 10, 2012

I is for Impatiens Downy Mildew – Is this the end of Impatiens?

Every January I attend the local Green Industry trade show.  I go to meet up with people, find out what new products are available in the industry and learn about new plants, new techniques, anything new.  This year there was big news, but it wasn’t good.

For many years Impatiens have been a staple in shade gardens.  The blossoms range in everything from fuchsia to pink to white, peach and salmon, even oranges and reds.  They brighten up shady spots, they’re used in pots, in flower beds, even in mass plantings.  Whether  your favorites are the traditional singles, the doubles, the semi-doubles or those with variegated foliage there’s something for just about everyone. But sadly, those days may be nearing the end for us.

Impatiens, specifically Impatiens walleriana, now have an enemy.  Impatiens Downy Mildew.  This Downy Mildew is a water mold which spreads by spores traveling in water splashing from nearby plants and unfortunately the spores also travel on the wind, transferring them from neighboring landscapes.  The prominent times for plants to get this Downy Mildew are in the spring and the fall, when temps are cool the air is damp or when there is a lot of rain.  Once the plants have Downy Mildew, the leaves will start yellowing or have a stippled effect, the underside of the leaves will have the white, downy (fuzzy looking) mildew.  Next, the leaves will begin to curl, almost taking on the look of an over-watered plant, then the plants will drop all of their leaves and their flowers leaving just empty stems.  Finally, the stems will turn to mush and collapse, leaving nothing looking much like they got hit by frost.

The sad part about Impatiens Downy Mildew once they get it, they will not recover.  There’s nothing you can do.

Impatiens Downy Mildew is spreading across the whole country quite quickly.  This disease initially appeared in the US in 2004, but in small quantities, more occurrences appeared in 2007 and 2008, predominantly in greenhouses.  In 2011, it started appearing everywhere.  The hardest hit areas were in the Northeast, in Cape Code, in Florida, Michigan, Wisconsin, the Twin Cities in MN and in Southern California.

As of right now the only prevention is really at the greenhouse level, where they are applying fungicides.  But they have to be careful and rotate which fungicides they use because there are certain fungicides that were used in the UK, that this mildew has now become resistant to.  On a residential level, there really isn’t any way to prevent your plants from getting it and there is no treatment once they have it.

If they get it, you need to pull the plant and destroy it (put in the garbage bag, tie it off and dispose of it, DO NOT COMPOST IT!).

So where does this leave us?  As you plan your garden this year, due to the alarming rate this is spreading, and the fact the Twin Cities was hit so hard with it last year, I would recommend skipping Impatiens altogether and plant an alternative in its place.  Some good alternatives to Impatiens (that can handle similar conditions in the Upper Midwest) are Coleus, Snapdragon, Alyssum, Salvias, Pansies, Violas, Begonias (both Wax Begonias and Tuberous Begonias), Geraniums, Ipomoea, Nicotiana, Lobelia and New Guinea Impatiens, to name a few.

Yes, you did see New Guinea Impatiens on the alternative list.  Why?  Because New Guinea Impatiens (Impatiens hawkerii) are not effected by downy mildew and have been successfully grown in greenhouses and landscape beds even under high disease pressure for downy mildew.  Yea!

But what if you don’t want to change?  What if you always plant Impatiens?  If you really love Impatiens and want to take the chance, then go for it, but consider yourself warned.  You’ll have to check with your local nurseries and garden centers to see if they still carry them.  But be aware that even if you buy healthy plants, they can still get hit with it at any time during the season, (especially if you live in one of the areas that were prominently hit last year) and it would be a huge bummer to plant them and nurture them only to have them wither before your very eyes.

Not the best news to share, but thought you all should be aware.  If you’re interested in learning more about this and following new information that comes out, the American Floral Endowment if following this disease and any new findings from Universities and other industry specialists.  Included is a link for a nice presentation of what Impatiens Downy Mildew looks like, along with a summary of the disease history, and biological info put together by Ball.