How to Get Rid of Powdery Mildew: Organic Treatment and Prevention

By Deanna Talerico updated Jun. 29th, 2026, published Apr. 29th, 2021

Come learn how to get rid of powdery mildew in your garden. I live in an area where powdery mildew is incredibly persistent, so I’ll share my top tips to prevent mildew, reduce its spread, and the organic treatment methods I use to keep my garden looking beautiful, healthy and productive.

I’ve also included how to identify powdery mildew, its favored conditions, and what plants are most susceptible (or resistant!) to help you better manage it. Or, skip straight to the prevention and treatment options here.

What is Powdery Mildew?

Powdery mildew (also known as “PM”) is a common fungal disease that can affect a wide variety of edible crops, flowers, and ornamental plants. Though it goes by one collective name, powdery mildew can be caused by several different species of fungi.

Powdery mildew appears as white powdery mold spots on plant leaves. As the fungus feeds and robs nutrients from the plant, it causes stunting and reduced vigor. This stress can also make the plant more vulnerable to other diseases or pest damage.

If powdery mildew coats a significant portion of leaves it can inhibit photosynthesis – slowly starving the plant. A change in photosynthesis can also negatively impact crop flavor as the plant produces less sugars.

A close up image of a squash plant with a heavy infestation of powdery mildew. The leaves are caked with a whitish silver coating that resemble spray paint. — A very severe case of powdery mildew on zucchini in my neighbor’s garden. Do NOT let mildew get this bad in yours! (I would treat or remove the plant far before this stage)

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Ideal conditions for PM and how it spreads

Powdery mildew can be found in virtually every growing zone, though it especially thrives in climates with prolonged periods of warm dry weather with a touch of humidity. The dampness of humid air (or evening fog/dew) encourages the fungi to grow, and the warm dry air during the day helps the spores spread.

Powdery mildew spores primarily live on plants, but can also survive or overwinter in soil, compost, mulch, or other plant debris. The spores spread from plant to plant (or, are initially introduced into your garden) by wind, insects, splashing water or direct contact from infected plants.

Crowding plants, lack of airflow, and shade also increase the risk for powdery mildew.

A watering can that isn't visible is watering the soil below the canopy of collard greens so the water isn't getting on the plant's leaves. The water resembles that of a rain shower spray. — Providing good airflow between plants and avoiding wetting plant leaves helps to reduce the spread of PM.

Identifying Powdery Mildew on Plants

Powdery mildew appears as light grey or white, dusty-looking spots or blotches. The spots are usually round, fuzzy, sometimes slightly raised, and typically start on leaves and stems before moving to the flowers or fruit themselves. The infected leaves may eventually turn yellow and dry out too. In severe cases, the plant looks like it’s been dusted in powdered sugar or flour.

Powdery mildew is sometimes confused with downy mildew, which causes darker yellow-brown spots on leaves instead.

Keep in mind that natural leaf patterns can sometimes look a lot like mildew too! Some varieties of zucchini, squash, and melon plants have natural white spots or variegation on their leaves. (See example photo below.) If you need help identifying the difference between powdery mildew vs natural white spots on leaves, see this post.

A small cucumber seedling is showing small splotches of powdery mildew on its leaves. Two small yellow flowers are emanating from the main stem below the leaves. Powdery mildew favors plants in the cucurbit family. — Powdery mildew spots on cucumber leaves

A two part image collage, the first image shows the top leaf of a PM resistant variety of squash. There are natural gray variegation on the leaves that are fairly symmetrical across the whole leaf. The second image shows DeannaCat turning the leaf over so you can see the underside which looks green and healthy where as plants inflicted with PM will usually have spots on the undersides of their leaves as well. — This is a perfectly healthy zucchini leaf, believe it or not. It just happens to have a natural variegated pattern that resembles PM at first glance.

What plants get powdery mildew?

Powdery mildew can inflict over 1000 different plant species including many common vegetables, flowers, and ornamental plants.

Plants that are especially susceptible to get powdery mildew include squash (both summer squash like zucchini and hard squash such as pumpkins or butternut), melons, cucumbers, tomatoes, eggplant, peppers, kale, peas, beans, lettuce, strawberries, grapes, mustard greens, carrots (the greens), apple trees, and many flowers including zinnia, calendula, roses, sunflowers, peonies and hydrangeas.

I’ve found that cabbage, cauliflower, broccoli, bok choy, and collards may get a little PM, but not nearly as bad as the aforementioned plants.

Some plants that are resistant or do not readily get powdery mildew include avocados, citrus trees, garlic, and many herbs – including basil, sage, lavender, rosemary, thyme, oregano, dill and more.

A large Dunja zucchini variety plant is featured. It's leaves are more than twice the width of a large hand. Many green fruit are growing amongst its base with a few flowers mixed in as well. Surrounding the squash are many calendula and borage with yellow and purple flowers. Beyond in other raised beds lie onions, collard greens, an array of calendula flowers, pole beans and zinnia. A wall of flowering salvia make up the background with pink flowers dotted amongst the green foliage. — Another perfectly healthy squash plant with natural leaf patterns that look similar to PM. In fact, this Dunja zucchini variety is resistant to powdery mildew – a prized cultivar in our summer garden.

7 Ways to Prevent Powdery Mildew

Here are several ways I’ve found help prevent powdery mildew in my garden. In fact, they’re often so effective at keeping it to minimum that I rarely need to treat for it!

Choose plants and varieties that are naturally resistant to powdery mildew. Reading plant descriptions or seed packets, you can find many varieties of mildew-resistant zucchini, melon, tomatoes, zinnia and more. They won’t be totally immune but are effected far less. For instance, Dunja is my go-to zucchini variety – it rarely gets mildew, while most squash in our garden does.
Practice good plant spacing. PM thrives in humid, crowded conditions. Prevent powdery mildew from spreading between plants by reducing overcrowding. Follow spacing recommendations for each type of plant, and prune plants as needed to increase airflow and reduce touching between them. Mildew also grows most readily in the shade, so provide susceptible plants plenty of sunshine.
Don’t compost diseased plants. Instead, put them in the trash or municipal green waste bin. Powdery mildew spores can survive in your compost and will spread to other areas of your garden when you use the compost later.
Clean your garden tools! It’s always a good idea to routinely sanitize your garden tools (e.g. pruning shears), especially when you’re working around diseased plants. To prevent powdery mildew from spreading, I always use rubbing alcohol, white vinegar, hydrogen peroxide, dilute bleach, or another sanitizing agent to wipe down tools before moving on to the next plant.
Wet the soil, not your plants! As much as possible, avoid watering plants overhead. Constantly damp leaves or splashing water from an already-infected plant encourages the growth and spread of powdery mildew. Instead, water the soil below the plant. Get my guide on how to install drip irrigation for raised garden beds here.
Use companion planting and crop rotation. If you know you struggle with powdery mildew, don’t plant a bunch of plants that are highly-prone to PM all together in one bed. Buffer and interplant them with resistant species. Learn more about garden companion planting here – printable chart included! It’s also important to practice crop rotation, especially after a bought of PM.
Promote overall healthy plants and immune systems. Healthy, well-nourished plants are more resilient to fend off disease – including mildew. To keep my garden happy and healthy, I routinely amend our garden soil with organic fertilizers and well-aged compost, and water with homemade compost tea and aloe vera extract. Develop a consistent watering schedule and avoid drought stress too.

Raised garden beds are set against a greenish blue house, the beds are lush with a variety of plants growing in them from chard, to calendula, to pole beans growing up a metal trellis. Zinnia and sunflower plants are growing up towards the setting sun while more calendula and borage is growing along the ground in front of the beds leading to a dazzling array of flowers that are purple, pink, orange, and yellow. Prevent powdery mildew by maximizing companion planting. — An example of wise companion planting: Swiss chard (usually resistant to powdery mildew, at least in our garden!) sandwiched between pole beans and calendula in back and front – two crops that are very prone to PM. Planting other susceptible crops like bush beans, kale, collard greens, or eggplant in the place of the Swiss chard would have been asking for trouble.

5 Ways to Get Rid of Powdery Mildew

Now, here are 5 organic ways to treat or get rid of powdery mildew. There are all sorts of other “hacks” out there, but these are the most effective options in my experience. (I’ve tried the suggestion of spraying plants with milk… and all it did was make my plants smell like rotten milk.)

Cut and remove infected leaves. If caught early enough (and as long as the plant can survive without the infected part) the simple act of pruning off a few infected leaves can often halt or drastically slow the spread of powdery mildew to the rest of the plant. Just be sure to clean your pruning shears well before and after!
Spray the plant with baking soda. Sodium bicarbonate (baking soda) changes the pH of the leaves, making them more alkaline and less hospitable for the fungus to thrive. Thoroughly mix 1 to 2 tablespoons of baking soda per 1 gallon of water plus 1 tablespoon of liquid castile soap or dawn dish soap (which helps the baking soda spread and stick to the leaves better) and then spray the plant down, saturating both the tops and bottoms of leaves.*
Use potassium bicarbonate. This is the most effective organic treatment for powdery mildew I’ve found! Potassium bicarbonate has a similar method of action to baking soda (raises pH to inhibit spore growth), but is even stronger and longer-lasting. Once I treated young seedlings that developed mildew very early on, and after just one application they stayed PM-free for the rest of growing season! Mix 1 Tbsp of potassium bicarbonate powder and 1 Tbsp of liquid soap in 1 gallon of water. Add it to your favorite sprayer, shake it all up, then spray everything down – coating all parts of the plant.*
Neem oil spray – In my experience, neem oil slows down the spread of powdery mildew, but doesn’t usually cure an established infection. I personally don’t love to use neem oil directly on tender foliage that I’m going to eat (like kale leaves) or veggies with a lot of nooks ‘n crannies (such as broccoli) because it can leave an oily residue that isn’t always easy to wash off. However, it’s great for for the leaves of squash plants! Neem oil must be diluted and applied carefully*. Learn exactly how to properly emulsify, mix, and use neem oil spray here.
Trash infected plants. If all else fails, it is best to completely remove significantly infected plants from your garden to stop the spread of disease. Use caution and common sense during removal: avoid shaking the plants about, dragging them over other plants or prime soil, or anything else that would cause the fungi spores spread even more. Remember, don’t add these to your compost heap.

*For any type of foliar spray treatment, I always recommend waiting to apply it until the evening hours – once the plant is out of direct sunlight. Bright sun on wet leaves can cause scorching. Also, beneficial insects are typically less active during the evening to dusk hours. Though all of these treatment options are considered safe and organic, it’s best not to directly spray beneficial insects with them.

A pump sprayer is sitting on the corner of a raised garden bed, Aaron's hand is reaching into the image holding the wand of the sprayer as he applies a foliar spray to prevent or treat powdery mildew onto bush beans that are growing in the raised bed. There are other plants in the bed including more bush beans and kale. In another garden bed next to it there are tomatoes, peppers, and onions growing. The evening sun is just about setting below the horizon as a yellow orange glow recedes amongst the shadows. — Spraying down mildewy bush beans with potassium bicarbonate.

Can you eat vegetables that have powdery mildew?

In general, powdery mildew isn’t harmful to people. Meaning, it is not toxic or poisonous. Although, some folks are sensitive or even allergic to mildews and mold, so it’s wise to proceed with caution.

Since mildew is quite common in my garden, I’ve definitely eaten plants with a few spots of mildew! (I hate the idea of wasting food). I simply wash the produce well before eating it, but avoid consuming severely infected parts.

DeannaCat is holding a leaf of lacinato kale that has be inflicted with powdery mildew. The raised white and fuzzy growth is stretching across the length of the leaf. — Here is a moderate case of powdery mildew on kale leaves. Also note the smaller white spots on the leaves in the background. I would personally not eat leaves with this much mildew on it.

And that concludes this lesson on organic powdery mildew management.

All in all, don’t worry if your plants get a few spots of mildew. It’s almost to be expected! We’ve learned to accept and peacefully co-exist with the relentless fungi in our garden, yet do try to be proactive about keeping it to a minimum. I hope this article gave you plenty of ideas of how to do just that. Feel free to ask any questions in the comments below.

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51 Comments

Sarah

April 17, 2025 at 10:22 pm Reply

Hi Aaron 🙂 I started my weekly EM-1 foliar sprays maybe 2-3 weeks ago? I started with it on my tomatoes and anything getting hardened off, but expanded to everything on the patio for prevention efforts. I have some calendula seedlings that are about 3-4″ tall that just started to present PM. It makes me uneasy because of my situation: we rent and we have grass and sprinklers. This creates a lovely micro-environment for fungal issues. If it was my house, there would be no grass problem solved! But since it’s not – I’m wondering if 2x/weekly em-1 foliar sprays would be an ok thing to do in this very particular time of year in 10b near the coast with the cold nights and AM/PM fog + warm sunny days? Is that overkill? Was thinking could go back to 1x/week when this more severe gloom/warm sun cycle breaks later in the summer. I’m trying v hard to prevent PM this year. Thanks for any guidance you can give!
- Aaron (Mr. DeannaCat)
  
  April 18, 2025 at 8:10 am Reply
  
  Hi Sarah, we are all to familiar with the climate you are growing in, while you can likely foliar spray EM-1 twice a week, once a week is the general recommendation. We typically end up spraying EM-1 on our entire garden as well. For your calendula plants, since they are still fairly small and are already showing PM, you may want to spray them with the potassium bicarbonate for a week or two in a row and see if that helps stave off the PM for now. Know that calendula are incredibly PM prone and we almost always get PM on our calendula at some point, no matter what we do. However, the plants will continue to grow and produce, even with PM, though they will look at tad more unsightly. Also, PM is typically specific to whatever plant it is growing on so even if you have PM on your calendula, it won’t necessarily be the same PM that could end up on your tomatoes or squash. Hope that helps and good luck!
  - Sarah
    
    April 18, 2025 at 9:34 am Reply
    
    Thank you!!! I read the same about the weekly foliar sprays, only doing max 3x/week if it’s raining heavily. I hit the calendula with some 3-in-1 and just decided this batch will have to stay out of the veggie bed, since I was already out spraying my sweet peas for PM… oh, the PM… do you have to reapply the potassium bicarbonate weekly like a typical fungicide?
    - Aaron (Mr. DeannaCat)
      
      April 18, 2025 at 9:46 am Reply
      
      Hi Sarah, potassium bicarbonate is sprayed only once a week, you could keep up with a weekly foliar for your more PM prone plants (calendula and peas).
Sarah

March 21, 2025 at 6:49 am Reply

Hello from 10b! Does the potassium bicarbonate work for PM on tomatoes as well? Thank you! Bought some with your link 😊
- Aaron (Mr. DeannaCat)
  
  March 21, 2025 at 7:26 am Reply
  
  Hi Sarah, yes it does! Last summer, we sprayed out tomatoes with EM-1 (a microbial inoculate) once a week as a preventative measure and it seemed to do a great job as well, although maybe a tad more work. Hope that helps and have fun growing!
  - Sarah
    
    March 21, 2025 at 8:06 am Reply
    
    Aaron! You read my mind. I’d prefer a preventative! What’s the dilution you used for it? And does it work for blight? Thank you!!!
    - Aaron (Mr. DeannaCat)
      
      March 21, 2025 at 9:13 am Reply
      
      Hi Sarah, we were surprised how well it seemed to help out the whole garden, potassium bicarbonate is good to still use on occasion once you see PM present on your plants. EM-1 is typically used at 1 ounce per gallon of water, you can use it to water your plants and/or as a foliar spray. Since our garden is fairly large, we find the foliar spray to be the easiest method as we can’t hand water everything but it could be useful to water your tomatoes with it on occasion as well.
      
      You can also “activate” EM-1 using molasses and water in a separate container which essentially ferments it where you can turn a small amount of EM-1 into a larger amount, I can’t remember the exact ratios but I would use 6 or 8 ounces of EM-1 along with the same amount of molasses in a one gallon container that I would then fill with water, essentially creating one gallon of EM-1 with only 6 ounces of the original. However, if you do this, the resulting EM-1 that you activated only lasts 1 to 2 months so you want to be able to use it all within that timeframe as it isn’t shelf stable like the original EM-1 bottle.
      
      Anyway, EM-1 is a whole other thing that we can likely talk about in an article itself, do some research and look into it yourself to see what you can do with it all. We were adding it to our donkey manure last year as well as it can also act as a compost accelerator. Hope that helps and maybe you will go down the EM-1 rabbit hole, good luck and have fun growing!
      - Sarah
        
        March 21, 2025 at 1:12 pm
        
        Aaron!!! I hugely appreciate the detailed reply. I bought some with your link. I will be going down the EM-1 rabbit hole 🕳️ I was listening to a podcast from a local gardener and she was saying she had used a fungi rich compost tea to use as a folier spray and she didn’t get any fugal diseases on her tomatoes that year! But then she never shared what she used… thanks again for the knowledge 😊
      - Aaron (Mr. DeannaCat)
        
        March 21, 2025 at 10:26 pm
        
        So great to hear Sarah and we hope you that you have success using EM-1 in your garden and it helps with any fungal diseases that you may normally see!
Dolores Madden

August 11, 2024 at 10:13 pm Reply

My Zucchini, Crookneck and Delicata Squash plants suddenly developed a moderate case of powdery mildew which led me to read about how to manage it . Oddly, shortly after noticing the mildew, I also noticed the presence of 10-20 very small beetles cruising around on the leaves of each plant. They are so smal it’s hard to photograph them so I couldn’t use a photo ID App to determine the species. Initially I was concerned that they were going to be like cucumber beetles and feed on the leaves and I started to consider what to spray on them. But, instead I did an online search of beetles in CA which led me to the Ten Spotted Ladybeetle which feeds on mildew. So, no need to spray and I hope they multiply sufficiently to make a dent in the powdery mildew! I’m curious to know if you or any of your readers have ever seen these tiny beetles in your garden.
- Aaron (Mr. DeannaCat)
  
  August 12, 2024 at 7:29 am Reply
  
  Hi Dolores, that’s great if you do have some mildew eating lady beetles in your garden! We haven’t really noticed any of those in our garden specifically but they would be more than welcome here, we don’t typically spray for pests much outside of a soap spray for aphids when necessary. Thanks for sharing your experience and have fun growing!
Luz

July 23, 2024 at 1:23 am Reply

Hi Aaron,
I come back every year to this useful article. Thanks ! May I ask how often should I apply the potassium bicarbonate treatment ?
Regards,
Luz
- Aaron (Mr. DeannaCat)
  
  July 23, 2024 at 7:23 am Reply
  
  Hi Luz, so great to hear you find our article so helpful! You can apply the spray weekly or once every two weeks if everything is looking good. Have fun growing!
JENNA C ALI

May 28, 2024 at 3:06 pm Reply

All of the Palo Verde trees in So Cal have PM this year. I never knew it affected trees until now!
- Luz
  
  July 24, 2024 at 2:27 pm Reply
  
  Hi and thanks for your prompt answer !
Douglas Shane

May 26, 2024 at 8:21 am Reply

As always, this article about powdery mildew – both the text and photos – are absolutely helpful!

You may well be the best gardening site on the Web!

Keep on keepin’ on!
- Aaron (Mr. DeannaCat)
  
  May 26, 2024 at 9:20 am Reply
  
  Thank you so much Douglas, glad you find our content so helpful and have fun growing!
Heather Koltko

August 2, 2023 at 5:18 pm Reply

Thank you for this great article and tips!!
Deborah

July 28, 2023 at 8:24 am Reply

How often should or can the potassium bicarbonate be applied?
- Aaron (Mr. DeannaCat)
  
  July 28, 2023 at 8:39 am Reply
  
  Hi Deborah, applying it weekly should be sufficient. Hope that helps and good luck!
Shefali Gupta

May 28, 2023 at 12:53 pm Reply

Thank you for this great article.

Would be great if you could talk about rust in the garden. I have been dealing with it for the past 3-4 years on my Fine Leaf Buckthorn and this year it surfaced on one of the roses. I’ve sprayed with neem oil but it doesn’t seem to work. I’ve also used copper fungicide by Bonide with no luck.
- Aaron (Mr. DeannaCat)
  
  May 29, 2023 at 7:50 am Reply
  
  Hi Shefali, we get some rust on occasion on our garlic and leeks while also seeing it on some of the grass/weeds on our property. I am surprised copper didn’t work for you but you could also try micronized sulfur, for the copper and sulfur sprays, when you apply the spray may also have a direct correlation on the spray working to control your rust issue. Some need to be used as a preventative versus using it to solve the problem. We have removed plants in the past that just don’t seem to do well in our climate, if a plant consistently gets rust or powdery mildew, we typically decide to move on from it and grow something else. Check out this response to treating the disease for fine line buckthorn, hope that helps and good luck!
Brenda

October 14, 2022 at 11:16 pm Reply

Hi, we planted a butterfly garden this year with new plants, including coreopsis which have bloomed and become covered in powdery mildew. We are in zone 7. Should we cut the plants to the ground and hope they will come back next year? Is it too late to spray the plants w/o cutting them? What would you suggest? TIA
Brenda in PA
- Aaron (Mr. DeannaCat)
  
  October 15, 2022 at 8:24 am Reply
  
  Hi Brenda, it really depends on the type of coreopsis you have as some can be annuals (they only live for one season) while others are perennials (will last for a number of years). Since you are in zone 7, I am sure you will be getting into some colder weather here shortly so if the coreopsis is a perennial, once frost hits, it is recommended to cut the plant back to about 6 inches above ground. Once spring and warmer weather hits, the plant will take off with new growth. Hope that helps and good luck!