Powdery Mildew – Prevention and Treatments for Your Vegetable Garden

Powdery mildew is an extremely common plant disease and can affect any vegetable garden, whether you have a small backyard operation or acres of crops. But don’t fret! It is also one of the most recognizable plant diseases so you can catch it at an early stage.

What is Powdery Mildew?

Powdery Mildew can be caused by a variety of fungi species, but is identified by the powdery appearance of the fungus growth on the leaves, stems, and flowers of the plant. All powdery mildews enjoy the same damp and humid climate but each fungi is host specific. Meaning, the fungi that affects your squash plants is not the same fungi that can spread to your fruit trees.

Powdery mildew is not typically fatal, but will leach nutrients from the plant and weaken it – leaving it susceptible to other disease and insects. If the leaves become covered with powdery mildew it will block photosynthesis, causing leaves to turn yellow, wilt, and prematurely drop. Inadequate photosynthesis will diminish the plant’s capability to produce flavorful fruit, if at all.

What Causes Powdery Mildew?

Powdery mildew fungi is everywhere and can be introduced to your garden via wind, insects, birds, or water. As mentioned above, powdery mildew thrives in damp, warm environments. Combine these conditions with crowded plants and poor air circulation and you get a fungi breeding ground.

We have personally dealt with powdery mildew as the air circulation is not great where our garden is located. It is very close to the house which blocks the breeze completely and we have sunken beds (rather than raised beds) so the air does not circulate near the base of the plants and lower leaves very well. Our garden also only gets approximately 6 hours of direct sunlight rather than the preferred 8 hours. I will talk about some prevention tips and remedies that I have found useful so that maybe it will save you all some research time.

How to Treat Powdery Mildew

First, remove any leaves that are too wilted and diseased to save. I found a couple remedies using food grade Potassium Bicarbonate which is safe to use (and consume if it does get on your veggies). The recipe I use is for a 32oz spray bottle:

• 1 teaspoon potassium bicarbonate
• 1 teaspoon vegetable oil
• 1/4 teaspoon of non-detergent liquid soap
• Fill the remainder of the bottle with water.

The simpler version of the recipe I use is 4 teaspoons of potassium bicarbonate into 1 gallon of water. Spray directly onto foliage to eliminate and prevent powdery mildew.

I have also seen recipes using baking soda instead of potassium bicarbonate but these recipes are more effective for prevention rather than eliminating an existing problem. If you have a history of powdery mildew in your garden in years prior, it’s not a bad idea to use this recipe as prevention:

• 1 tablespoon of baking soda
• 1/2 teaspoon of liquid, non-detergent soap
• 1 gallon of water

Preventing Powdery Mildew

• Pruning and thinning your plants will enhance air circulation.
• Clean your clippers after pruning.
• Try and find a cultivar that is powder mildew resistant.
• Do not crowd your plants. Leave some breathing room between your crops.
• Plant susceptible plants in full sun in order for the foliage to remain dry.
• Water your plants at soil level. Watering from above can spread fungi spores and damp foliage is a breeding ground for fungi.
• Never use infected leaves or stems in your compost. It will continue to re-infect your plants year after year.

Fruits and Vegetables Most Susceptible to Powdery Mildew: