Let’s Talk About Powdery Mildew

— Written By Bill Hanlin and last updated by JoAnne Gryder

powdery mildewLast week I did an article about early blight on tomatoes. Gardeners know there are a number of diseases that infect plants, including the one I am going to write about today. Powdery mildew is a disease that can infect a wide variety of plants including vegetables and ornamentals.

Powdery mildew starts off as a yellow spot on the leaf and, on most plants, will develop into a whitish powdery mass on plant leaves and stems. Powdery mildew can cause different symptoms depending on the infected plant. If left untreated, these symptoms can range from distorted growth on dogwoods to yellow or dead leaves on vegetables.

Unlike many other diseases, powdery mildew does not require wet conditions to infect the plant. This disease is favored by temperatures between 60 to 80 degrees F and high humidity. Shade also contributes to powdery mildew infections.

There are a number of ways that gardeners can minimize the impact of powdery mildew on their gardens. There are resistant varieties of ornamentals and vegetables that can be planted. For example, most oriental dogwoods are resistant to powdery mildew infections.

Plants should be grown in full sun. Space out your vegetable plants to encourage good air flow throughout the garden. Also, pick off and dispose of infected leaves

There are some fungicides that are effective in preventing powdery mildew infections. Most of these fungicides need to be applied before infection to protect the plant.

Horticultural oils have been shown to eradicate powdery mildew infections. Read the label before applying since some oils may damage the plant if applied when temperatures are above 90 degrees F.