What is Powdery Mildew

Have you noticed some white, powdery spots showing up on some of your plants? This could potentially be a fungal disease known as ‘Powdery Mildew’. This disease is a common problem in gardens and can affect a wide variety of plants, and if the infection is severe enough, can reduce the quality and quantity of flowers and fruit on the plant.

A variety of plants can be affected by powdery mildew, including, but not limited to:
Squash
Pumpkins
Cucumbers
Melons
Tomatoes
Eggplant
Peppers
Beans
Peas
Roses
Dahlias
Impatiens

Powdery mildew visible on these cucumber leaves.

As the fungus grows on the plant, a layer of mildew (made up of many spores) starts to form across the top of the leaves. These ‘powdery’ spores are carried to other plants by the wind, or by touch. If you’ve had Powdery Mildew in your garden before, spores can lie dormant in old plant material or weeds nearby. Powdery mildew spores require live plant tissue to grow and reproduce.

The powdery mildew fungus thrives in warm temperatures (15-27 degrees celsius), dry climates, but with high relative humidity to spread. Higher temperatures and cooler, rainy areas slow down the spread of the fungus.

To help control Powdery Mildew, remove old plant material in the fall to help remove any spores from the area. Increasing air flow and sunlight to the plants will also help prevent Powdery Mildew from spreading. Chemical control is not often required, but if you do choose to treat it, chemicals for Powdery Mildew containing sulphur, myclobutanil, chlorothalonil, tryfloxystrobin or thiophanate-methyl can be used. Be sure to check labels for specific species each chemical can be applied with as well as application instructions.

Information for this was obtained from the following sources: