I had a customer contact
me a couple weeks ago saying they noticed thier imaptiens were tall and leggy
with little or no blooms. I went out to inspect it and thought it looked like
they were suffering their normal end of season blues two MONTHS too
early.
Very concerned I
contacted our very trusted supplier Mindy Clesen at Ron Clesen's
Ornamental Plants Inc. and she informed me that last year we saw the
beginning of what is turning out to be a very significant epidemic for
impatiens.
She and a fellow
employee, Rachel Prescott, have given me the following useful
information.
- Downy mildew won’t occur until the conditions are perfect. Most people
think since they haven’t seen it yet this summer that everything will be fine,
however, the cold nights are really what trigger the disease to start taking its
toll on plants
- Downy mildew is characterized with leaving only the stalks of the
plants left in the bed: flowers and leaves will drop, and most of the time the
leaves will be covered in white spores on the underside
- The best thing to do when you identify the disease is to remove ALL
plants from the bed. The most important part of this step is to do it as soon as
you can! The mistake I saw a lot of landscapers make last year was they waited a
week until their crew was back at the house or jobsite to remove the plant
material. There are two very important reasons why you should remove the
material right away:
- There are two types of spores that are produced by Downy Mildew. The
oospores are the spores that overwinter in the soil, and can cause Downy Mildew
in the bed year after year once they’ve settled in. By removing material right
away you are trying to prevent the overwintering of these spores.
- The other type of spores are airborne spores. These airborne spores
will die if they do not find another host, and in this case they would have to
find another impatiens to infect. The quicker you remove the infected material,
the less likely the disease will spread to a neighboring
bed.
- Unfortunately there is no data about if throwing
infected material into your compost pile will affect the
integrity of the compost. Ball has said to just throw the material away in the
garbage if you can, that way you don’t have to worry about your compost being
compromised.
- Downy mildew of impatiens only infects Impatiens walleriana, the
standard impatiens. New Guinea impatiens, impatiens hawkerii are highly tolerant
of the disease. No other plants are infected by this pathogen. So choosing a
different species of annual in 2013 is a good idea.
- Plasmopara obducens produces tough survival spores called
oospores that can overwinter in soil and plant debris. As a result if downy
mildew was present in your garden last year, it is likely to show up again in
2013. Downy mildew can also move in on wind blown spores. Although it is not
known how far the downy mildew pathogen can travel by wind, a close relative,
downy mildew of cucurbits, has been shown to move over 600 miles in 48
hrs.
