My peony turned gray this year. It happened kind of
suddenly in September. I've never seen this before. Is it something
to be worried about? Should I do anything special to them this fall
or next year? The peonies were my mother's so I don't want to lose
them. - O.E. -
Powdery mildew can afflict a peony and this year in some regions
environmental conditions afforded that fungus the perfect
opportunity. We, too, saw it crop up where we've never seen it
We have cut or will cut all those peonies to the ground and put
the debris into a hot compost to destroy the fungal spores. Chances
are it won't be a regular occurrence but by reducing the amount of
material that harbors the spores, we hedge our bets.
Mildew, by the way, is often gray or white on a leaf but it can
simply turn a leaf yellow, brown or bronze.
The fungus first consumes some of the leaf's essence and then
"blooms" with the white or gray fuzz when conditions are right.
However, if the leaf dies before the fungi mature, or if the leaf
is partially damaged but has the power to resist the infection --
perhaps by producing chemicals that stall or stop the fungus --
then it may show these other colors.
Here are mildew-infected leaves we saw this year.
Please note that all of this damage happened as a result of
mildew fungi but numerous fungus species were involved. Some of
these fungi can infect many different species of plants, some have
a more limited host range. So when you see mildew on a number of
unrelated plants, it may not be spreading between them like a flu
spreads between people. It's more often the case that the
environment in the area simply favors fungal development and has
opened the door to each plant's own curse. In that situation a
change in that environment is a better solution than tackling each
plant's affliction. Improving light, air flow, irrigation patterns
or switching to resistant plant species may prevent infection,
which is the best method for handling fungal problems.
Not all peonies developed mildew, and some were not such hotbeds
of sporulation as the one at the top of this page. This level of
visible mildew was more common:
Flowering dogwood (Cornus florida)
There is a dusty look to the leaf surface, and some scorch where
mildew-ravaged tissues were more sensitive to heat than healthier
Tall phlox (Phlox paniculata)
Mildew usually infects a leaf long before we see its white or
gray stage. If the mildew takes enough out of the leaf before
conditions are right for the fungus to form its fuzzy,
spore-producing coating, the leaf will brown and die.
Pardon our dust - more photos to