Powdery
mildew, which looks like a dusting of gray-white
powder on leaves and is a particular plague of crape
myrtles and roses, hit some areas hard this year. The
good news: If the "powder" hasn't already
disappeared, it soon will. The bad news: It probably
will be back next spring.
Powdery
mildew (Erysiphe lagerstroemia) is a fungus that
thrives in spring, when there is lots of moisture and
days get warm. Young, growing shoots of plants can dry
up and shrivel, flower buds may drop, leaves may curl.
Mature growth also takes a hit, but less so. Once
summer arrives, the fungus struggles.
And
while powdery mildew badly disfigures crape myrtles
and roses, usually the fungus won't kill plants; it
just looks awful.
"Powdery
mildew is something you see every year," says Dr.
Raul Cabrera, an associate professor and project
leader in woody ornamental horticulture at Texas
AgriLife Research and Extension in Dallas. "It's
just unsightly. For most folks, they want to do
something."
The
best course of action, the experts agree, is
prevention.
"The
best weapon against the situation is to rely on plant
cultivars that are tolerant or resistant," says
Dr. Cabrera. New crape myrtle cultivars, for instance,
have greater resistance to powdery mildew than the
common varieties that have been grown for years and
invariably get powdery mildew. (Most of the newer
varieties have American Indian names, so they are easy
to recognize at nurseries.) Roses that have earned the
EarthKind designation also count disease-resistance
among their attributes.
Other
tricks in the homeowner's arsenal:
Location
- Plant ornamental plants where they will get good air
circulation.
Plant
roses and crape myrtles in full sun.
In
fall, remove affected leaves, to avoid spread of the
fungus.
Don't
overfertilize.
Prune
lightly, thinning out branches and removing broken or
rubbing branches to promote good air movement.
If you
can't stand the sight of powdery mildew in spring, get
on a regular program of spraying fungicides, natural
or chemical.
Dr.
Kevin Ong, assistant professor and AgriLife urban
plant pathologist, says there are a number of
fungicides to control powdery mildew.
Many
chemical fungicides can be sprayed on plants to keep
it in check. Organic remedies include Neem oil extract
and potassium bicarbonate, a cousin of baking soda.
You can even make your own potassium bicarbonate spray
by mixing it at a rate of 4 teaspoons per gallon of
water.
But
don't spray it or other fungicides on plants during
the hot part of the day, Ong warns, as this could burn
the leaves.
Even
though the fungus abates in hot weather, the pathogen
is still hanging around, waiting for better
environmental conditions. So put control of powdery
mildew on your to-do list - for spring.