As you peer over your zucchini 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 jeans 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.
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.
🥒 FRUIT & VEGETABLES PRONE TO POWDERY MILDEW
- Fruit trees
🌻 Ornamentals Prone to Powdery Mildew
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.
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.
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.
→Follow me on Instagram where I often make a fool of myself←
Now if only I could actually grow zucchini - I'm apparently the only person in the world who can't. One year, to everyone's horror, I had 21 plants. And I actually got 4 little zucchini! My farmers market vendor offered to hire me to control their crop!
Ha! My mom always says that she plants two and prays that one dies!
I learned the hard way that less is more. I had 4 plants in my 4' x 4' raised bed garden and got hit with mildew and harvested just 4 zukes!
Yes, yes, yes.. dreaded powder mildew... sorry, I can't concentrate because I am waiting for the stunning conclusion of the Restoration Hardware furniture hack! You are a total tease, Karen! You are killing meeeeeeee.
Vinegar?! Can you spray at any time or just when the sun doesn't hit? I've been spraying with the same epsom salt/ water solution I use on tomatoes and peppers and my zuke leaves are a gorgeous green still. I use 1 tbsp/gallon and spray at any time, even midday. Seems to help.
My hot peppers are not only in such an abundance, but are mighty hot, as well. The hot summer as well as the (I'm told) epsom mix makes them hotter. And bigger, as in 5" jalapenos.
Any ideas for hot peppers? Hot P jelly only uses about 1/2 cup worth and I have about 4 lbs...!
Cowboy Candy? It's really jalapeño slices processed with sugar. I really burned up my hands and face slicing 3 pounds of jalapeños that I lost any enthusiasm for them and gave them away! Didn't even taste them. Just Google Cowboy Candy, there are plenty of recipes.
It REALLY REALLY works, although I did put 1tbsp (did not kill the plant). Thanks a lot, and I will try the "potion" on bee balm and other mildew prone plants.
Great stuff! Vinegar is such a versatile, useful and eco friendly household item (window washing, cutting board cleaning etc.)
Summer of doing stuff indeed! Can't wait to see you finished outdoor bench à la RH.
Thanks for the tips. One year I lost my plants to bugs, the next year I let my garden rest, and the year after that, powdery mildew! So no garden this year but I will next year with the help of your tips. Thanks again, Karen!
Does the vinigar work on tomatoes also?
Hi Aaron. This solution works for powdery mildew on anything but remember it has to be mixed, not straight vinegar. And make sure what you have is actually powdery mildew and not blight on your tomatoes. If it's blight the best thing I've found for that is (removing all the affected tomato leaves) and them spraying it with Serenade Disease Control. ~ karen!
Tomatoes don’t normally get mildew, they suffer from early and late blight, also a fungal disease that is best PREVENTED by making a proper compost tea (takes ~24 hours with a tea brewer - see link below) from healthy vermicompost or a good correctly made thermophilic compost - brought to you by your friendly red wriggler earthworms - you can buy it most places - or make your own. You spray it on the leaves, top and bottom, as soon as the plants start to grow. This also works against powdery mildew. You spray it as soon as you make it as it won’t keep, but once sprayed, the microbes will continue to grow and cover new leaves as they are fed by the plant’s exudates on the leaves. I give mine a boost about once a month.
I thought vinegar was used to kill plants? Am I wrong?
It would kill plants if you sprayed it on full strength. But this minuscule amount only kills the mildew. ~ karen!
Please educate us on how to care for capsicums
Are there any videos further explaining the staking & pruning of zucchini?
There isn't a video yet Jim, just the photos and explanation in this post on How to Stake Zucchini.
I have a zucchini that was planted May 9. It is full of male blossoms but not one female blossom. According to the instructions that came with the plant, I was supposed to be able to harvest in 48 days. Any ideas as to what can be wrong?
HI Pat. It was just a little slow to start. Zucchini always start by putting out male blooms first. It will start to put out females very soon (maybe even already since your comment is a few days old). Once the female bloom is pollinated several day slater you'll have a full grown zucchini. :) ~ karen!
I was wondering if I could use Apple Cider Vinegar instead of white vinegar?
I haven't tried it so I can't say for sure, but I don't see any reason why it wouldn't work. :) ~ karen!
I will try the spray on my plants today but......”Ann with an E!!”
OMG-decided to try it last night....so wonderful! cried through most of the episode where Anne runs away....
thx for another addiction!
Thanks Karen. Only 1 of my phlox plants has it and yes it’s the only one in the shady part of the garden. I will try this mixture immediately in my empty (and clean) Febreze ONE air and fabric container. It’s the best for producing a perfect spray/mist. I don’t buy “fake” air fresheners, choosing instead natural bees wax and/or oils BUT when at a cottage a few years ago there was one there and I thought it would do in a pinch... the container is the best part. Anyhoo... thought I’d share that little tidbit ;)
Thanks! ~ karen
Hi! Just wondering what strength vinegar you use? Normal 5 or 6% cooking vinaigre or stronger? I have some 10% and some 14%.....
Just regular cooking vinegar. Not pickling or cleaning strength vinegar. ~ karen!
Better than vinegar.
I used the rak method and it immediately stopped the PwdMldw on the pumpkins and zucchini.
10 g Kosher Salt (1 TBS) per cup of water in a sprayer. Fine spray on leaves and mold is dead by morning. Keep a sprayer handy to prolong the freshness of purchased vegetables, plus a handy spritz of light seasoning for steamed vegetables.
This is the same brine used for cucumber lacto pickles and I was surprised that it did not harm the plants in the least. Must use a fine mist to avoid adding too much salt to the soil too rapidly. It really doesn't take much, just hit the mildew until wet.
I'll give it a shot for fun! ~ karen
Hi I was wondering what your suggestions are to prevent and get rid of Alphids!
A spray of ivory soap is for bugs.
Cut a little sliver off a bar, drop in spray bottle, add distilled (or cooled off boiled) water, shake, and your set!
Just remember to rinse anything you sprayed before eating! ;)
A strong brew of chamomile tea also works on fungus / mildew.
I usually brew 4-6 bags for 12-24 hours (boil 2 cups water, pour over tea bags in large glass cup/ jar, cover with foil, wrap with tea towel, & put some pot holders on top.)
Pour into spray bottle, add a pinch of baking soda - optional, and cut a small sliver of dad's ivory soap bar (lol;) & drop that in. Top off with more water to fill the spray bottle.
Works on bugs too, so an all round spray.
You do have to use it often however.
Powdery mildew… gone!
Now they die in a day… bore worms!
I trust your wisdom!!
You are my garden 🧙
I think that’s a witch or wizard … something magical! Not a gnome…they are a bit creepy. Why do people like them?
Hi Sue. Sorry about your vines! Yes, squash vine borer can seem to kill a squash plant almost overnight. If you have more you can use this method to deal with it. https://www.theartofdoingstuff.com/squash-vine-borer-control/ ~ karen!
Thank you, Karen! This (the vinegar potion) worked for me. Wish I’d seen it last year. Just about everything in my garden got PM last year: tomatoes, zucchini, cucumbers, beans, etc. We started calling it my Covid garden. I searched for treatments for tomatoes, and the only solution I could find was Bonide Organic Fungicide, a total oxymoron if you ask me. Nonetheless I used it, and what a pain on all those big plants, top and bottom of leaves. It took forever. The mildew didn’t affect my yields much, except I got sunscald on some tomatoes after cutting off too many sickly leaves. Anyway, this year I noticed it first on my zucchini, searched for that and found your post. I was so happy when it worked! I also trimmed the lower leaves like you said, and I’ve got tons of beautiful zukes. Thank you for sharing this potion!!!
Excellent, I'm happy to hear that! ~ karen
Does the vinegar and water solution have to be reaplied? Cut away all the mildew leaves and sprayed the remaining ones yesterday. Hoping to save my plants.
For years I have Black Eye Susan's that their leaves get brown spots. Those spots get larger and larger resulting in leave that are totally brown and crispy. This only happens on my Susan's. And, it doesn't matter where in my backyard they are. I have probably 6 areas both in the ground and in containers and they all get it. No other variety of any other plants have this. I cannot get a good diagnosis or help of any kind. Anyone have suggestions?