Impatiens are one of the most common
and colorful bedding plants in the United States. If you've seen your
lush, full colorful impatiens fade and wither to scrawny stalks,
you've seen Downy Mildew (IDM) up close. It is a plant disease
(specifically a fungal-like pathogen) that is spreading. Downy mildew
was spotted on impatiens on both coasts last year.
Powdery or Downy?
Since downy and
powdery mildews are managed differently, it's really important to identify
the issue correctly.
Downy mildew:
Appears very rapidly and is
difficult to control.
Found on the underside of leaves
Causes the leaves and flower
petals to drop off, and begins with leaf stippling, downward
curling of leaves and leaf yellowing. After losing their petals and
leaves, infected plants will die and appear like they had heavy
frost damage.
Also affects basil, coleus,
snapdragon, salvia, alyssum, pansy, rose, rosemary, and ornamental
cabbage, and Perennials including aster, coreopsis, geranium, geum,
lamium, potentilla, veronica and viola.
Powdery mildew:
Can occur on either the upper or
lower surface.
Spreads slower than downy
mildew.
Causes minor long-term damage, stunting growth.
Different species affect different plants/crops.
Powdery mildews are most severe when the weather is warm and dry, and
they affect virtually all kinds of plants: cereals and grasses, vegetables,
flowers, weeds, shrubs, fruit trees, and broad-leaved shade and forest trees.
Many plants have been developed to be resistant to or tolerant of powdery
mildew.
GOOD NEWS: New Guinea Impatiens
(Impatiens hawkeri) are resistant. Next
year, you can plant them in rotation with susceptible
impatiens in fresh planting beds.
Largely considered a minor nuisance
since the 1940s, DMI has been known from scattered and minor
occurrences in the U.S. beginning in 2008 it began to spread in
eastern parts of the U.S. It is a type of “water mold” that is
weather dependent requiring humid, moist
conditions and spreads by both airborne and water spores.
Without a susceptible host the
pathogen will eventually die off in the planting bed.
To prevent the disease from living in
your soil over the winter and returning next year:
Remove and dispose of infected plants
(roots included) immediately.
Don't compost the infected plant
material.
Speaking of next year, plan to plant your impatiens in different flowerbeds to
avoid a re-occurrence of the disease.
It
is safe to plant other flowering or foliage plants in affected
beds next season.
Don't give up hope, with a few adjustments, common garden impatiens will continue to be a mainstay of our landscapes.
Sources:
Information compiled by Renee C. Brannigan
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