Powdery mildew is caused by a fungus. It can be airborne or remain dormant in garden beds until conditions are right. There are several varieties that attack different species of plants. Powdery mildew leeches nutrients and strength from your plants causing them to become weaker and produce fewer flowers. Eventually it will kill your plants. There are easy organic formulas to prevent and treat powdery mildew.

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Invariably I plant vegetables that are susceptible to powdery mildew. In past years applying commercial sprays met with little to no success. The past two years I have all but eliminated synthetics from my garden, opting instead for a healthier organic approach.

To create a less hospitable environment the trusty electric chainsaw on a pole was employed to lop and and trim trees along the back of the house. This allows more light to filter through to the garden and more air to circulate.


Aggressively prune plants in the garden to allow for sunlight and airflow throughout. Powdery mildew like many fungi prefers dark, humid conditions. Don’t go chopping and hacking your veges willy-nilly. Each plant species has a specific method of pruning. Over pruning causes plants to go into shock and affects growth.


An auto-timer on a soaker hose to water the main vegetable bed is a new addition this year. The bed gets watered every two days starting at 6am. Watering with a soaker hose keeps the water close to the roots of the plants, and diminishes water on the foliage. Water drops on top of foliage act like a magnifying glass. In direct sunlight water on foliage can cause leaf burn.


As soon as powdery mildew appeared on my butternut squash, I started searching the net for an organic solution. There are a lot of suggested home remedies. I eventually had to make an educated guess on what would work for me.

The formula I settled on was: 1TB baking soda, 1TB dish soap, 2TB vegetable oil added to 1 gallon water. Shake it up. Put it in a sprayer and liberally spray the top and bottom of your plants leaves. Make sure you spray in the evenings.

This is one time where watering in the evening is encouraged. The reason to spray in the evening is so the plant does not get burned by the sun. As mentioned before, water on a plant acts like a magnifying glass when the sun hits it, burning the plant.


The baking soda changes the ph. on the plant making it inhospitable to the fungus. The oil holds the baking soda, and the dish soap works as an emulsifier, evenly spreading the active ingredients. You will notice results as early as the next morning.

Repeat after 3 days if there is still powdery mildew growing. After that, repeat as needed, usually every 5-7 days. For me, this recipe worked wonders. I have only had to use this 3 times to keep my squash and cucumber healthy through active growing and production.

Plants are dying back now, now is the time to just let them go. These plants are not actively growing any longer, and the vegetables are just ripening by sun and warmth. As soon as motivation hits, the dying plants will go and winter plants will go in.


This recipe can be used to treat other plant ailments with slight tweaking. Effectively, this spray reduces the number of different chemicals and sprays that you would usually have to buy to treat separate pests and diseases.


At the end of the season DO NOT put the diseased plants in your compost or till back into the garden. Destroy the plants some other way. The fungus will spread if you mulch the plants back into your garden, or put them in the compost. The spores can remain inactive for a long time.

I had great success with this homemade solution to powdery mildew. Give it a try and let me know how it worked for you.

You may be amused to read about my total heirloom tomato failure this year.

Click here to download the free data sheet with organic recipe and spray calendar.

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