Downy mildew is sometimes
confused with another fungal disease called
powdery mildew.
The main difference in the two is the location of the
symptoms.
Powdery mildew appears as
a grayish, fine wood ash colored covering on the TOP of
the leaf.
Downy mildew appears on
the BOTTOM of the leaf where it forms irregular yellow
to dark brown lesions. In the presence of high humidity,
it will produce spores of white, tan, gray or purple
which gives it a "downy" appearance.
There are several species
of fungi that cause downy mildew and there appears to be
a different species for each host plant species. Also,
some species of this organism can persist in the soil
for long periods of time.
In recent years,
outbreaks of downy mildew have been found in impatiens,
coleus, basil and several other ornamental plants not
previously known to be bothered.
