Powdery Mildew: Treatment and Control on Plants

Powdery mildew is one of the most common diseases to impact plants. While almost no type of plant is immune, certain species are more susceptible than others. Luckily, there are effective powdery mildew treatments that can help fight the disease.

Luckily, powdery mildew can be treated early on with fungicides including potassium bicarbonate, neem oil, sulfur, or copper. Home remedies like baking soda and milk can work as successful treatments when applied properly.

Below, learn more about identifying powdery mildew, treatment options, and how to prevent it from showing up in the first place.

What Is Powdery Mildew?

Powdery mildew is a fungal disease in plants that is commonly seen in warm, dry climates and causes a white-gray, powdery substance to appear on leaves. Several different species of fungi can cause powdery mildew.

Identification and Symptoms

As the name implies, powdery mildew presents itself as dusty splotches of white or gray powder on the leaves and stems of infected plants.

Although powdery mildew can impact a variety of different kinds of plants, each fungal infection is "host-specific," meaning the breed of fungi infecting that plant is specific to that varietal. Translation: the powdery mildew on your lilacs will not spread to different varieties of plants in your garden.

Symptoms of powdery mildew on your plants can include:

• Splotches on the surface of leaves: These are often the most obvious signs of powdery mildew. However, the disease typically starts on the undersides of leaves, often appearing on the stems, flower buds, and even fruit.
• Withering and yellow leaves: This happens because powdery mildew can leech important nutrients from the plant.
• Fallen leaves: If enough of the leaf surface becomes covered with powdery mildew, photosynthesis is impaired, and the infected leaves will drop from the plant prematurely.
• Impaired flavor: For edible plants, like fruits or vegetables, insufficient photosynthesis can diminish the amount of sugars produced, ultimately affecting flavor.
  

Powdery Mildew Causes

Powdery mildew fungi can be found anywhere, but conditions favoring it include high relative humidity at night, low relative humidity during the day, and temperatures of 70-80 degrees. These conditions prevail in spring and fall.

The spores are carried by air currents and insects such as woolly aphids and germinate on the leaf surfaces when there are extended periods of warm temperatures paired with dry conditions. The fungi spores reside in plant buds. They can also overwinter in plant debris and become transported to your plants via wind, insects, and splashing water.

Powdery Mildew Treatment

While removing and destroying all infected plants is the ideal solution, it's not very practical. Luckily, there are less drastic measures you can take to rid your garden of these pesky fungi. Learn more about these below.

Remove infected portions of plants

First, before using fungicides, you'll want to remove the infected parts of your plants. Below are the correct steps:

• First, remove or cut back the portions of your plants with visible powdery mildew: Use plant clippers to do so.
• Remove individual leaves from the affected plants: Do not compost them because this can allow the spores to spread.
• Wash your hands and clean your clippers with alcohol wipes: This will further prevent the spread of the disease.

Apply a Fungicide

Remove powdery mildew on plants by using fungicides that can specifically treat powdery mildew on plants. Look for one containing potassium bicarbonate, neem oil, sulfur, or copper. Homemade powdery mildew treatments are also an option such as:

• Vinegar: Vinegar can work as a fungicide because the acetic acid in the vinegar changes the fungus's pH, which will kill the disease. Mix four tablespoons of vinegar with one gallon of water to create a spray mixture. Reapply the vinegar fungicide every three days until the disease is gone.
• Milk: Milk can both treat and prevent powdery mildew. Simply create a spray bottle mixture of milk and water, with a 40/60 ratio of milk to water, and pour it into the spray bottle to spray on your plants.

For continuous protection, reapply fungicides every seven to 14 days, and follow the label instructions for both application and the waiting period before harvesting fruits and vegetables.

While fungicides won't cure powdery mildew, they can help stem the spread of the fungi to other leaves or plants.

Limit Spread With Baking Soda

You can use baking soda to limit the spread of powdery mildew. While baking soda alone isn't effective in controlling powdery mildew, it works well as a preventative when combined with liquid, non-detergent soap and water. Use the baking soda spray all over the plant.

It is less effective as a cure once the fungus has taken hold.

How to Prevent Powdery Mildew

The best defense against powdery mildew is to follow these best practices to maintain an environment that does not encourage mildew growth:

• Choose healthy plants and work to keep them that way: Stressed plants, whether from drought, overwatering, or other poor growing conditions, are an invitation to disease.
• Purchase powdery mildew-resistant cultivars: This is especially important if you garden is in an area that is known to be susceptible to powdery mildew.
• Avoid planting susceptible plant varieties in the shade: Plants that remain damp offer spores an ideal place to grow.
• Improve your garden's air circulation: Thin and prune each plant until they seem to have "room to breathe." This practice can help prevent the spread and growth of any fungi already present.
• Do not fertilize affected plants until the powdery mildew outbreak is under control: The spores favor young, succulent growth, so fertilizing a plant while an infection is still present can actually increase the spread.
• Avoid watering plants from above: Wet leaves might encourage more mildew growth. Some powdery mildew are inhibited by moisture on leaves while others are favored by wetness on leaf surfaces.
  

Plants Likely to Be Infected by Powdery Mildew

Plants that are notably susceptible include lilacs, flowering crab apple trees, tall garden phlox, bee balm, roses, squash, cucumbers, and zinnias.