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Avoiding and treating powdery mildew

Powdery mildew symptoms and treatments

Powdery mildew is a fungus that belongs to the Erysiphaceae family and frequently colonizes certain plants.

This mold appears in the form of a light velvety white layer or white spots on leaves, which is what makes it immediately recognizable.

What makes powdery mildew appear and spread?

Powdery mildew spreads most easily when warm weather and high relative humidity occur together.

It usually appears in Spring, in April or May, when temperatures rise and the soil and air are still full of moisture from the wet months of March and April.

It also makes a comeback at the beginning of fall, when nights grow longer and moisture once again increases.

  • While it’s difficult to control temperature, you can work towards reducing air moisture.

How to treat powdery mildew

Powdery mildew should be treated both through preventive and curative actions.

Preventive actions

These actions will keep powdery mildew from appearing, or at least delay its spread.

  • Ensure proper air circulation in your plant beds, to avoid stagnating moisture.
  • Spread sprouts apart or thin seedlings out if they sprout too densely. Powdery mildew spreads when plants are tightly packed together…
  • Remove infected portions immediately. Burn them or discard them, but don’t compost anything contaminated.
  • Avoid overwatering, increase soil drainage – excess soil moisture makes plant “perspire” more. They try to evacuate excess root water through leaves. This is far too welcoming to powdery mildew spores!

Curative actions

Once powdery mildew has appeared, it’s possible to contain and stop it.

  • Eventually, spray with fungicides.
  • When dealing with vegetables, favor organic treatments instead of chemical ones:
  • Milk. Mix ½ quart (½ liter) milk to 4½ quarts (4½ liter) water (total 5 quarts (5 liters)), spray every week until the disease is wiped out! This is a great stay-at-home solution that can help you garden during lockdown.

Powdery mildew agents are usually specific to the plant they infect: powdery mildew on grape vines will not contaminate your rose trees.

Plants vulnerable to powdery mildew

Trees and shrubs most often infected with powdery mildew are:
oak trees, maples, maule’s quince, apple trees, pear trees, rose bushes, peach trees, hawthorn, red currant bushes, and grapevines.

In the vegetable patch, powdery mildew often spreads on the following plants:
radish, leek, corn, strawberry plants, zucchini, pickles, carrots, eggplants, red beets, endives, cucumbers and potatoes.

There are even herb spices that can contract powdery mildew:


powdery mildewThis picture shows powdery mildew on grape leaves and fruits.

See also:

Fighting aphids

Organic caterpillar control

Fighting scale insects

Fighting fruit flies

Fighting cherry flies

Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Symptoms of this fungus by Scot Nelson under Public Domain
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