As you peer over your zucchini or rose leaves you notice white spots. Hmm. Weird you think. A few days later the whole leaf looks white and more and more of them are covered in spots. You have powdery mildew. Well, your plant has it actually. Here's how to identify, treat and prevent powdery mildew.
I would like to draw your attention to the photo at the top of this post. There it is. The dreaded powdery mildew. Be GONE! Be GONE I say!
That didn't work at all. Although it might have worked on my favourite sunglasses because I can't find those.
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.
Table of Contents
🍃 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.
🙅♀️ How to Prevent Powdery Mildew
So now that you know the conditions that powdery mildew likes, try your best to avoid those. How?
- Don't crowd your plants. Plants that are close together will have a high humidity and low light. These are idea conditions for stupid, stupid mildew spores.
- Keep your plants from being shaded. Shade = happy powdery mildew spores.
- 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.
- Get rid of any stakes or string you may have used as well that could be holding onto the spores.
Powdery Mildew Treatment
A simple mixture of water and vinegar won't cure powdery mildew but it will keep it in check.
Materials
- Spray bottle
- Vinegar
- Water
Instructions
- Mix together 4 cups of water + ½ Tablespoon of Vinegar in a spray bottle.
- Spray the top and bottom of all the plant's leaves once a week.
Notes
This really does work. I'm not speaking anecdotally. All my gardening techniques and tips are 100% tested and experienced by me in my own garden.
Why it works:
The reason behind the effectiveness of this spray is pretty simple. Powdery mildew can’t grow in wet conditions, so when you spray the leaves with water you’re creating a cruddy environment for them to grow in plus washing some of them literally off of the leaf.
The vinegar alters the pH of the water and spore that it hits which it also hates.
These two things combined are what stop the powdery mildew in its tracks.
Plants prone to Powdery Mildew
🥒 Fruit & Vegetables
- Melons
- Pumpkins
- Squash
- Pepper
- Beans
- Peas
- Cucumber
- Fruit trees
- Parsley
- Zucchini
- Grapes
- Lettuce
- Tomatoes
- Potatoes
🌻 Ornamentals
- Begonias
- Phlox
- Sunflowers
- Dahlia
- Roses
- Zinnia
- Peony
- Lilacs
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.
🚰 Powdery Mildew Treatment
4 cups of water + ½ Tablespoon of Vinegar.
Would you like to save this stuff?
We'll email you this post, so you can refer to it later.
Spray the top and bottom of the leaves once a week.
That's it. It's a pretty simple potion.
WHY IT WORKS
The reason behind the effectiveness of this spray is pretty simple. Powdery mildew can't grow in wet conditions, so when you spray the leaves with water you're creating a cruddy environment for them to grow in plus washing some of them literally off of the leaf.
The vinegar alters the pH of the water and spore that it hits which it also hates.
These two things combined are what stop the powdery mildew in its tracks.
Just fill a spray bottle with the water and vinegar solution and leave it in your garden so it's always there ready and willing to perform its potion duties.
** Milk and water also works, (recipe below) but you don't want a stinked up bottle of milk-water sitting around for days - which is why I opt for the vinegar solution**
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.
The other thing you should do to keep your zucchini healthy is to take its blood pressure regularly. No, wait, that's elderly parents.
No, with zucchini you should remove all the leaves that are below the fruit and stake it. You can read my whole guide to growing zucchini where I explain that you do indeed need to pinch and stake your zucchini plants, just like you do a tomato plant.
The photos in this post are from before I discovered staking zucchini.
Pruning the zucchini leaves that are full of powdery mildew should be done by the base of the vine. Don't worry about cutting them off. Any leaves below that lowest fruit can and should be removed even if they're perfectly healthy. You don't need those stinkin' leaves. And neither does the plant. The only thing you should be a bit careful about is that you cut the leaves off with a sharp knife or scissors and cut stem as close to the base as possible.
Becauseeeeee .... zucchini leaf stems are hollow, until they get right to the base of the plant. If you cut leaf stems off at a point where they're still hollow it's more prone to disease.
Disease a potion might not fix.
The growing zucchini are only using the stems ABOVE it for energy. The ones below the growing fruit do nothing other than look ugly, wither up, die, get powdery mildew and spread disease.
So they're useless. Get rid of them.
Do these two things, the potion and the proper staking and pruning and you'll be picking all summer.
(I've experimented with a lot of ways to reduce powdery mildew and this is the most effective and easiest. A solution of milk and water also works and even has some preventative qualities to it, but you can't leave a spray bottle of milk out in your garden for weeks. You have to mix it up fresh every use)
🥛 Milk Solution for Powdery Mildew
Mix a container with 60% water and 40% milk (or whey). Apply on top and underside of leaves weekly.
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 within a couple of weeks and you will soon be able to move onto shouting and swearing at your tomatoes.
gloria
Then there's the dreaded squash vine borer. These are the little nasties that can destroy your zucchini almost over-night. This summer I finally caught one in the act, which sent me on a research mission to find the best way to annihilate their butts. This video was very helpful. https://www.youtube.com/watch?v=1TV2WXwmqUs Now my zucchini garden is full of yellow bowls.
Mary W
Something else that I didn't know - another wonderful reason to be following you. I'm entertained, enlightened, and enspired. (Yea, I know but wanted to continue with the e words.) I miss the old Organic Gardening magazine where people shared this useful but not-for-profit information. You and natgeo - great reasons for becoming a couch potato. Course Forensic files is another but you just don't fit that classification.
Kelly
I don't know Mary. Maybe Forensic Files can track down the missing jeans?
Diane amick
Karen...for the last two posts an ad covers all narrative so that I can't read anything...photos are good, just no narrative. It says "5 Tips for better photography". Never happened before. Help!
Karen
For anything like that you have to take a screen shot and send it to me Diane so I can forward it to my ad people. karen@theartofdoingstuff.com I also need to know what device you're reading the post on and what browser. :) Thanks! ~ karen
Darlene
I don't have room for a garden but if one day I do I will be sure to remember this. More importantly though, where did you get that cute spray bottle??
Karen
Dollar store. ~ karen!
Elizabeth
Great tip Karen but I'm confused. At the beginning of the post it says 1 Tablespoon vinegar to 4cups water but in the video it says 1/2 tablespoon vinegar. Which is the correct amount ?
Alice
My question, too! I suspect the amount is not that critical -- as long as the solution is not too strong.
Linda in Illinois
I was just getting ready to mention that same thing.
Karen
It does matter Alice! Even just a little bit too much vinegar can burn the plants. :) ~ karen!
Karen
Sorry! It's 1/2 a tablespoon. I"ll correct the graphic up top. :) ~ karen!
Ronda
would this also work on peonies? mine get SOMEthing all over the leaves every summer after the flowers have bloomed. Doesn't seem to affect the plants, as they come back every spring with no problem. They just look very sad during the summer.
Susan
I wonder if the same potion will work for Rosemary? I would love to bring some in for the winter but every time I've tried, the Rosemary gets a white powdery film on it and does not do well. (As in dead by Christmas) It is beautiful and happy growing in fabric pots on my deck. It always seems to be such a shame to abandon the Rosemary to winter every year, but all of my attempts to bring it inside have failed. I will try Karen's magic potion.
Miriam Mc Nally
Adding some drops of Tea Tree (Melaleuca Alternifolia) oil (20-30 drops in 100ml bottle)to the mix will make it even more effective. Tea tree is a great anti-fungal oil.
I use this for black spot on my rose bushes, and it's good.
Would also recommend spraying on the stump when you cut off the leaves!
dede
Did you check your suitcase for your jeans?
Andrea
According to Mary Louise Flint, University of California at Davis, Director of UC Integrated Pest Management Education & Publications says, “A simple fungicide can be made at home by combining 2-1/2 tablespoons of horticultural oil (Sunspray Ultra-Fine, Saf-T-Side, etc.) in a gallon of water and adding 4 teaspoons baking soda. This solution is sprayed on plants to prevent powdery mildew infections." Respray after heavy rain, only use on foliage not soil. Works even on lilacs in the heat of the damp hot summers in Iowa, as well as edible garden plants.
Karen
Yes, some people like using baking soda. But since I've never actually used it myself I didn't talk about it. :) I tend only to talk about and recommend things I've actually tried and used as opposed to things I've read about. ~ karen!
Nancy Blue Moon
Nice organic solution Karen...but it won't entertain the neighbors like the first one...
Kathleen
I wonder if this potion sprayed in the face of irritating colleagues will get rid of them too? Perhaps just "pruning" them might work. They are like the leaves below the zucchini! :)
Seriously though, thank you for the handy tip Karen.
Mindy
Have you tried this potion on any perennials?
Karen
No, but it would work the same. My phlox normally gets powdery mildew in the beginning of the summer and dies a slow death but this year it didn't. ~ karen!
dee
My phlox has darned near been done right in by mildew-the weather in Ontario's been awful for it this year. I have tremors, so have lots of difficulty spraying both tops and bottoms of all those leaves. Do you know of something systemic that's not too evil Karen?
Karen
HI Dee! If you have tremors you can get pump bottles at Dollarama. You pump the handle up and down and then just hit the trigger button once and it continually sprays. :) I wish I could help you but I don't use any chemicals so I really have no idea what's useful for powdery mildew. :/ I'm not all high and mighty about it, I just don't use any chemicals. :) ~ karen!
dee
I haven't seen those in mine, but will check them out. I'm OK usually with the spray bottle, but have more trouble handling the tops/bottoms of the leaves thing. I usually do the vinegar/soap thing on the bee balm, but all the leaves on the phlox are trying my patience...
Lyn Richards
And then there's Powdery mildew-elimination Potion #9: a tablespoon of baking soda in a litre/quart of water -- same application, just spray it on. Has to be reapplied after rain. Anything that messes with the pH will do the trick.
Mary from Barrie
Thanks Lyn, you beat me to it - I've used the baking soda spray to get rid of powdery mildew on a clump of bee balm (Monarda). Stuff worked instantly since it altered the pH. I was amazed. Good to know vinegar will do the same thing.
Mary from Barrie
Oh, and this reminds me I have to get to my community garden plot to check on my zucchini! Didn't know about cutting off the leaves under the fruit - thanks Karen!!!
nancy
good to know because I don't love the smell of vinegar.
Rita
Fabulous tips! Will this also stop Blossom End Rot on the fruit (and get rid of age spots off my hands)?
Thank you Karen xxx
Karen
Ha! No. Neither. Sadly Blossom end rot is because of uneven watering (not low calcium in the soil as most people think) and age spots are caused by being old. ;) ~ karen!
Melissa
I knew you were magical, with your potions and whatnot. I'm gonna have the healthiest garden thanks to you!
Cynthia Jones
Brilliant.
May I humbly suggest adding a drop or two of dishwashing liquid to made the liquid adhere to the leaf for a little longer?
PS. How much should I charge a stranger to look after her hyperactive poodle for three weeks?
I am thinking $500-600. As usual, I err on the side of being "kind" but I am already imagining him jumping up and down at me first thing in the morning. I need to learn how to be kind to myself. So any input provided will be appreciated.
I know its nothing to do with zucchini, but I need help here guys.
Laurinda
It depends on if the dog is staying with you, or if you have to travel to it. Call a few kennels, ask for quotes, & charge only a bit less
Cynthia Jones
Good thinking 99. (Maxwell Smart quote).
TucsonPatty
On the contrary, I think you charge *more* than the kennels do because you are providing a service they are unable to provide. You are traveling to the dog's home, using your time and your gas or else you are using your home as a playground for that (hyperactive-furniture-leg-clothing destroying) dog. I watch animals for a friend, and it is a real service for them to not have to place the animal in a kennel. Sorry, Karen. Do you have a forwarding service? ; )
Cynthia Jones
That's true too. I know I would provide the very best service for both the dog and the human, so I suppose my only questioning should be. What kind of gain/reward am I going to provide for myself.
This will be a 504 hour job.
That's a lot of hours. I need to look at it like that.
Laurinda
It's the old 'Cutting People a Break Maneuver 99'
I had a birdsitting business, & that's how I priced it. I closed the business for a steady paycheck, but still have one client left. She refuses to let me go :-D
Karen
LOL. I have no idea. ~ karen!
Pam'a
It sounds to me like you're dreading it already. That's not likely to change. This person is a stranger. So if you really want to be "kind to yourself," just don't do it!
Penny
A stranger? Who owns a hyperactive, yappy dog? And she wants to get away from the annoying ball of fluff for three whole weeks? And did she ASK you to look after it?
Unless she can PROVE that she has copies of that sex-tape you made, just laugh at her and walk away.
Shirleygail
Remember to use a SOAP, not a dishwashing detergent. Detergent will burn, soap will not.
Before you agree to look after the dog, please be sure you are up for the challenge. Otherwise, it's not fair to the dog, or yourself. And if you do agree,
please remember it was your choice, and the dog mustn't suffer because you experience regret (and exhaustion) for agreeing. There are people who earn their living caring for dogs, that may be able to do some training work with him and send him home better behaved than when he arrived.
Gayle''
I get it! I always had mildew on my zucchini, and it probably was because of all those stinkin' unnecessary leaves. Thanks for the tip.
TucsonPatty
I always wondered what that powdery mildew looked like. Vinegar is an awesome mold and mildew eradicator (how about that word!) in all parts of your home, but I never thought of using it on plants. We get a nasty looking fungus-y thing on cactus here. I think I'll try it! Thanks for the tip!
Paula
Good tip but I wish it had been sooner :( I planted some more but I don't know if there will be enough time for them to grow. Oh well, I have my sights set on experimenting with season extension techniques.
Kathy
Great info,
I was wondering if I could use Apple Cider Vinegar instead of white vinegar?
Thanks,
Kathy