Powdery Mildew? Tips for Treating Molding Plants

August 14, 2015

Are your summer plants developing powdery mildew?  If so, come find out the causes of this common disease and how it can be prevented and treated!


What is Powdery Mildew, and How Does it Affect My Crops?

Powdery mildew is a fungus that can develop on a number of plants in the garden as late summer approaches.  It develops in spots that can eventually cover entire leaves of a plant in its powdery white veil.  While powdery mildew (PM) rarely kills its host plant, it does weaken it and can spread easily from one leaf to another, or even from plant to plant.

Which Plants are Most Affected?

PM most commonly affects squash, cucumber and strawberry leaves, but can also spread to peas, greens, or any other unlucky plants that happen to be near other infected plants.  There are several different species of PM, but they can all be treated and prevented the same way.

How Can I Prevent PM?

Powdery mildew often develops in the late summer.  Humid nights followed by dry, hot days create an environment where this fungus can thrive.  Overcrowded spaces and poor airflow are also breeding ground for PM.  Therefore, the best way to prevent it from developing is to plant your veggies with enough space to provide good airflow between plants.  For instance: Grown zucchini plants require 3-5 feet of space, winter squashes should be given plenty of space to trail outside of garden beds, and cucumbers can be trellised to maximize airflow between leaves!
Another great tip to prevent mildew is to use drip irrigation instead of overhead watering, and to water in the morning instead of the evening. This helps prevent PM by minimizing leaf dampness.


If powdery mildew has already affected your garden, here are a few ways you can treat it:

  • Baking Soda Solution: Mix 1 tablespoon baking soda with 1 tablespoon of biodegradable soap (we always use liquid Dr. Bronner’s castile soap – we recommend either peppermint or baby mild scent) into 1 gallon of water.  Mix/shake well and apply to affected leaves using a spray bottle.  Repeat twice a week.  (This method can also be used as a preventative measure.)
  • Compost tea: If you have access to compost tea from a worm bin, spray it on affected plants.  The good bacteria in the compost tea is anti-fungal!  Apply it twice a week.
  • Neem oil: Neem is a tree that is native to the Indian subcontinent.  Its oil can be used for several purposes in the garden: It has antifungal properties and can help control many garden pests including aphids and leaf miners.  1% neem oil sprays can be found at plant nurseries, as well as 70% neem oil concentrate that you can mix yourself with water.  Apply twice a week in the morning or evening – doing so at those times of the day will help to prevent oil burn on your leaves.
  • Milk: Like compost tea, milk also contains “good” bacteria that are antifungal.  We’ve never personally haven’t tried this method in our gardens, but we have heard of its ability to also clear PM organically.

If you’ve tried everything, and still find yourself frustrated with powdery mildew in your garden, reach out to us at StartOrganic and we will help you! Happy Summer planting!