HOW TO PREVENT AND CONTROL POWDERY MILDEW
By The
Editors
Photo by Pollinator: Wikimedia Commons
Wondering
about that white fungus on your plant? The fungal disease powdery
mildew is a common problem in gardens, infecting a wide variety of
plants and reducing the quality and quantity of flowers and fruit.
WHAT IS POWDERY MILDEW?
Powdery mildew is a fungal
disease that affects a wide variety of plants. There are many different species
of powdery mildew, and each species attacks a range of different plants.
In the garden, commonly affected plants include cucurbits (squash, pumpkins, cucumbers, melons),
nightshades (tomatoes, eggplants, peppers), roses,
and legumes (beans, peas).
When the fungus begins to
take over one of your plants, a layer of mildew made up of many spores forms
across the top of the leaves. These spores are then carried to other
plants by the wind. Powdery mildew can slow down the growth of your plant
and, if the infection is severe enough, will reduce fruit yield
and quality.
HOW DOES POWDERY MILDEW SPREAD?
Powdery mildew spores
typically drift into your garden with the wind, but if you’ve had powdery
mildew occur in the past, new outbreaks may also come from dormant spores in
old vegetative material or weeds nearby.
Unlike many other fungal
diseases, powdery mildew thrives in warm (60-80°F / 15-27°C), dry climates,
though it does require fairly high relative humidity (i.e., humidity around the
plant) to spread. In cooler, rainy areas, it does not spread as well, and it is
also slowed down by temperatures higher than 90°F (32°C). It tends to affect
plants in shady areas more than those in direct sun, too.
IDENTIFICATION
HOW TO IDENTIFY POWDERY
MILDEW DAMAGE
·
Plants infected with powdery mildew look as if they have
been dusted with flour.
·
Powdery mildew usually starts off as circular, powdery
white spots, which can appear on leaves, stems, and sometimes fruit.
·
Powdery mildew usually covers the upper part of the leaves,
but may grow on the undersides as well.
·
Young foliage is most susceptible to damage. Leaves turn yellow
and dry out.
·
The fungus might cause some leaves to twist, break, or
become disfigured.
·
The white spots of powdery mildew will spread to cover most of the
leaves or affected areas.
·
The leaves, buds, and growing tips will become disfigured as well.
These symptoms usually appear late in the growing season.
Powdery mildew first appears as small white spots on the upper part of the leaves. Photo Credit: The Regents of the University of California, UC Davis.
CONTROL
AND PREVENTION
HOW TO PREVENT POWDERY MILDEW
As with all pests and
diseases, the best means of controlling powdery mildew is
proactive prevention.
·
Choose plants for your garden that are resistant to powdery
mildew. Many mildew-resistant varieties of cucurbits (melons, cucumbers, squash, etc.) have been developed and can be
bought from major seed suppliers.
·
Plant in sunnier spots, as powdery mildew tends to develop more
often in shady areas.
·
Selectively prune overcrowded areas to increase air circulation
around your plants; this helps to reduce relative humidity.
·
Watering from overhead can help to wash spores off leaves.
Note, however, that wet foliage can often contribute to the development
of other common diseases, so it’s best not to
rely on this as a prevention tactic.
HOW TO CONTROL POWDERY MILDEW
·
Consider spraying infected plants with
protectant (preventative) fungicides. Effective organic fungicides for
treating powdery mildew include sulfur, lime-sulfur, neem oil, and
potassium bicarbonate. These are most effective when used prior to
infection or when you first see signs of the disease.
·
If you don’t want to use chemical fungicides, try spraying your
plants with a bicarbonate solution:
o Mix 1 teaspoon baking soda
in 1 quart of water. Spray plants thoroughly, as the solution will only kill
fungus that it comes into contact with.
·
Once plants are heavily infected, it’s very difficult to get rid
of the disease, so focus on preventing it from spreading to other plants.
Remove all infected foliage, stems, and fruit and destroy them,
either by throwing them in the trash or by burning. Remember, do not compost
any infected plant, as the disease can still be spread by the wind and persist
in the composted materials.
No comments:
Post a Comment