Powdery Mildew is caused by a fungus and, unlike many funguses; it can proliferate in hot dry conditions. It is recognizable by a white powdery growth of spores on leaf surface, followed by yellowing and dying of leaves.

Towards the end of a warm, dry spring you may start to see little dusty grey spots show up on leaves in your garden.  These dusty spots are a disease called Powdery Mildew.  This disease is caused by a fungus and, unlike many funguses; it tends to proliferate in hot dry conditions. It is recognizable by a white powdery growth of spores on leaf surface, followed by yellowing and dying of leaves.

This unsightly fungal disease affects a wide range of plants including ornamentals.  It stresses and weakens plants, which can affect the flavor and reduce yields of some fruits and vegetables. If enough of the plant surface is covered in the fungus photosynthesis can be inhibited and the plant can die prematurely. We find it most commonly occurring on cucumbers, peas, summer squash and winter squash, but can appear on almost any crop.

Fungal spores are spread by wind and overwinter on plants and in plant debris. Unlike mildews that appear in bathrooms or basements, powdery mildew does not need direct contact with water in order to grow. The warm days and cool nights of late summer create an ideal climate for spore growth and dispersal.

The fungi can overwinter in your garden on weeds or other debris.  Because of this, if your plant is heavily infected it is best to remove the entire plant from the garden.

Prevention:

• Rotate crops

• Plant varieties that are resistant to powdery mildew

• Allow for air flow by maintaining proper spacing between crops

• Clean up yellowing and dead foliage

• Work soil between plantings

Treatment:

• Remove affected leaves

• Baking soda spray: Spraying leaves with baking soda raises the pH, creating an inhospitable environment for powdery mildew.