How To Get Rid Of Powdery Mildew (Organic Treatment)

You notice white spots on your zucchini leaves. A few days later, it’s spreading. Then the whole plant looks like a powdered donut. You have powdery mildew. Or more specifically, your squash plant has it. And your zucchini. And maybe your roses, peas, and every other poor sap in your garden.

Shouting and swearing is probably your first response when you see any disease on your plant's leaves but that isn't going to do anything to stop the problem.

Shouting and swearing will help get rid of an unwanted cat in your garden or spouse in your bed but it ain't gonna do anything to get rid of powdery mildew.

It's not just zucchini that's susceptible - a whole slew of plants and flowers can be killed by powdery mildew. And even though you THINK it's caused by wet weather - it isn't.

🍃 What is Powdery Mildew?

There are actually all different types of powdery mildew that affect different plants. Cucurbits have their own type, phlox its own and so on.

It's caused by different fungi spores that make their way to your plants through the air and from splashing up from the soil when it rains.

The fungi alone isn't  harmful, but once it gets onto your plants it germinates and starts feeding by sucking nutrients from the surface of the plant leaves. That's why the leaves from a plant with powdery mildew eventually start turning yellow, crispy and die. They've had all the nutrients sucked out of them.

Powdery Mildew likes low light and temperatures from 20°- 30°C  (68°- 86°F) with high humidity (over 95%.) However when the temperature gets above 32°C (90°C) some of the spores die.  So it likes hot weather but slightly hotter than hot weather will kill it.

Unlike most mold and mildew that you think of, powdery mildew actually thrives in DRY conditions. It doesn't like or reproduce well when wet.

Humidity makes powdery mildew worse but heavy rain or soaking with a hose makes it better!

🙅‍♀️ How to Prevent Powdery Mildew

So now that you  know the conditions that powdery mildew likes, try your best to avoid those.  How?  

1. Don't crowd your plants.  Plants that are close together will have a higher humidity and lower light. These are idea conditions for stupid, stupid mildew spores.
2. Keep your plants from being shaded. Shade = happy powdery mildew spores.
3. Clean up ALL plant debris at the end of the year to prevent spores from overwintering in your garden. At the end of the season remove your infected plants and any dead leaf debris around them, put them in a plastic bag and take them right out of the garden to the dump.
4. Ideally, get rid of any stakes or string you may have used as well that could be holding onto the spores. But I mean, you're never actually going to get rid of the spores. They're everywhere. So I'd personally just keep using the same stakes and string.

🌿 Plants Most Affected by Powdery Mildew

Powdery mildew doesn’t just show up on squash and zucchini. It can show up on vegetables, fruit, flowers — even trees.
If you’re seeing mildew across your garden, here are the usual targets:

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Since jumping up and down and screaming doesn't work to treat powdery mildew you're going to have to mix up a potion to spray on the leaves.  Like a witch.  Or a Cher.  Cher seems like a potion maker.

Because the disease only affects the very surface of the leaves, a foliar spray treatment works really well.

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✨ How to Get Rid of Powdery Mildew (That Actually Works)

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🚿 Powdery Mildew Treatments

This, by the way, would be a great time to use the battery operated spray nozzle I talk about.

Vinegar Spray

• 4 cups of water + ½ Tablespoon of vinegar
• Spray the top and bottom of leaves once a week
• Store spray bottle in the garden for easy reuse

Milk Spray

• 60% water + 40% milk (or whey)
• Spray the top and underside of leaves once a week
• Must be mixed fresh for each use (milk goes gross in the sun)

Why These Work

Powdery mildew can't grow in wet conditions. When you spray the leaves, you're making the surface hostile and washing spores away. Vinegar also lowers the pH slightly, which the spores hate.

Milk has preventative qualities too, but unless you enjoy the smell of warm curdled dairy, you'll want to use it immediately and not let it sit around in a bottle.

I use the vinegar solution because it’s easy, effective, and garden-bottle-friendly.

It takes one minute to spray an entire zucchini plant. That's less time than you spend cursing at your zucchini plant because it produces so many zucchini you've started to force yourself to eat zucchini cereal every morning.

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Zucchini Pruning & Staking

Keeping zucchini healthy means doing two things: removing the lower leaves and staking the plant. You can read my whole guide to growing zucchini  where I explain pinching and staking a zucchini plant in more detail but this is the gist of it.

Why Prune?

• Any leaves below the first fruit can be removed, even if they look healthy.
• These lower leaves aren't doing anything helpful. In fact, they often end up with powdery mildew.
• Removing them improves air circulation and reduces disease spread.

How to Prune

• Use sharp scissors or a knife.
• Cut leaf stems as close to the base of the plant as possible.
• Zucchini leaf stems are hollow. Cutting them mid-stem leaves them prone to rot or disease.

Why Stake?

• Staking keeps the plant upright and improves airflow, which mildew hates.
• It also keeps leaves off the soil (where spores splash up).
• I didn’t stake in the photos here, but I do now. Here’s how I stake zucchini like a tomato plant.

Do these things — the potion, the staking and the pruning — and you'll be picking all summer.

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Now of course, if your plant is getting powdery mildew but you're already so sick of zucchini that the thought of them is making you gaggy, you should go with your original inclination of shouting and swearing at the plant.  

The plant'll be dead from powdery mildew within a couple of weeks and you'll be able to move on to shouting and swearing at your tomatoes.