Powdery mildew is one of the most commonly occurring plant problems. It is a fungal disease that affects plant leaves and stems, coating them in what looks like a white or gray powder-like substance. In severe cases, powdery mildew can even spread to the buds, flowers, and fruits of plants. Although any plant can get powdery mildew, some are very susceptible—such as crab apples, cucumbers and all types of squash, lilacs, phlox, and roses.
The white coating greatly diminishes the appearance of the plant, but it is not fatal unless left uncontrolled. However, as it spreads, it stresses and weakens the plant and makes it hard for photosynthesis to occur.
Controlling Powdery Mildew With Baking Soda
Baking soda has long been used as an inexpensive control for powdery mildew on plants. Unfortunately, baking soda fungicide is most effective as a preventative, offering only minimal benefits after your plants have become infected. If you know which plants are susceptible, spraying them weekly with the baking soda recipe, during humid or damp weather, can greatly reduce the incidence of powdery mildew in your garden.
To control powdery mildew on plants, mix together the following:
- 1 tablespoon of baking soda
- 1/2 teaspoon of liquid soap
- 1 gallon of water
Do not store unused mixture. While this recipe has been known to be effective, it can burn the leaves of some plants. It is recommended that you water your infected plants well a couple of days before applying this mixture, and don’t apply it in full sun. Try on a small area first, to test the plant’s response before spraying the entire plant.
Some recipes also recommend applying one tablespoon of ultralight horticultural oil to the mixture. The oil coats and smothers the fungi. The soap is added to help the mix spread and cling to the leaf surface. Be sure to apply to lower leaf surfaces as well.
Control Versus Cure
Unfortunately, this baking soda mixture works best as a preventative, applied before powdery mildew has a chance to spread on your plant. It is less effective as a cure once the fungus has taken hold. If you know a plant is affected by powdery mildew year after year, as is the case with many monarda, phlox, and lilacs, then spraying early in the season may prevent any occurrence that year. It is still worth trying after signs of powdery mildew appear, but it might not get rid of all the fungus.
Spraying plants with a milk mixture, after they have been infected with powdery mildew, is showing a lot of promise for actually killing the fungus. While so far no one is really sure why the milk mixture works it's worth a shot if preventative measures have failed.
Researchers are still studying the effects of using a baking soda mixture on other fungal diseases such as black spot, rust, and anthracnose.