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Organic Ways to Kill and Prevent White Powdery Mildew

Veggie Gardener

Preventing Powdery Mildew On Cucumbers, Squash & Melons

Posted on May 13, 2010 by Admin in Vegetable Gardening Tips // 62 Comments

Powdery mildew can be a real problem in the vegetable garden, especially for cucurbits such as cucumbers, squash, melons and pumpkins. Powdery mildew is a fungus that forms as a white or gray powder on the leaves of plants causing the leaves to become deformed and die. It is far more probable in areas that are damp, are somewhat shady, and have higher levels of humidity.

It is difficult to control powdery mildew once it begins spreading on the plant leaves. This makes it very important to use proactive measures in your vegetable garden to prevent powdery mildew from forming if you’ve had powdery mildew issues in the past. Here are some ways to prevent powdery mildew from overtaking your cucurbits.

powdery mildew cucumbers
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Steps For Preventing Powdery Mildew On Cucurbits

Here are some general guidelines you should follow in your vegetable garden to help prevent powdery mildew.

    • Select curcubits that are powdery mildew resistant, like the ones listed below:
      • Cucumber: ‘Diva’
      • Yellow Summer Squash: ‘Success’, ‘Sunray’, ‘Sunglo’
      • Zucchini: ‘Ambassador’, ‘Wildcat’
      • Pumpkin: ’18 Karat Gold’, ‘Gladiator’

 

    • Plant cucurbits in full sunlight. The powdery mildew spores have a difficult time surviving in direct sunlight.
    • Provide plants with sufficient spacing. Cucurbits need proper spacing to increase air circulation and to help prevent powdery mildew spores from spreading from one plant to the next.
    • Disinfect any tools after working around cucurbits. If you use a tool around summer squash, for instance, disinfect the tool before working around cucumbers. If the tool isn’t disinfected properly the powdery mildew spores could mistakenly be passed from one plant to the other. Disinfect tools with full strength vinegar or a solution of one part bleach to nine parts water.
    • Avoid watering cucurbits in the evening. Allowing the leaves to remain damp over night can increase the likelihood of powdery mildew. Water plants in the morning so the leaves have a chance to dry out before dusk. It is better to water the soil around the plants and avoid getting the leaves wet.
    • If leaves begin showing signs of powdery mildew ( small white or gray spots on leaves) remove the infected leaves from the plant and discard in trash. It is not recommended to place infected leaves in a compost pile.

Homemade Sprays Containing Milk and Baking Soda

One of the simplest and most cost effective ways of preventing and controlling powdery mildew is using a spray of milk and baking soda, applied directly to the top and bottom sides of the plant leaves. The baking soda will increase the pH levels on the leaf surface which will make it difficult for the fungi spores to survive.

It is unclear how the milk actually affects the powdery mildew spores, but spraying milk on infected plant leaves with a solution of nine parts water to one part milk has shown to decrease powdery mildew by 90% . It has been reported that milk can boost the plant’s immune system, which also helps to fight powdery mildew and other diseases.

I have used a solution of milk, baking soda, and liquid dish detergent to effectively control powdery mildew in my own vegetable garden. Here is the spray recipe I use:

    • Using a hose end sprayer , remove the bottle from the sprayer.
    • Fill the bottle with 1/2 quart of milk (I typically use skim milk, but any milk will work)
    • Add 3 teaspoons of baking soda
    • Add one drop of liquid dish detergent
    • Mix contents well
    • Reattach bottle to sprayer. Attach sprayer to water hose and spray the top and bottom sides of infected leaves
    • Reapply solution once a week

If you typically have issues with powdery mildew on your cucurbits, I think it is important to begin treatments using the milk and baking soda sprays before the powdery mildew sets in. Using the spray before the symptoms of powdery mildew are seen is critical in preventing it from forming in your vegetable garden.

How do you prevent powdery mildew on your cucumbers, squash and melons? Please share your powdery mildew controls with us!






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58 Comments on Preventing Powdery Mildew On Cucumbers, Squash & Melons

  1. JohnI Schooler //

    March 28, 2011 at 6:58 pm // Reply

    I volunteer at Leu Gardens here in Orlando. We have a demonstration vegetable garden. Powdery mildew is really tough to control here due to the frequent rain and high humidity. Today I noticed that the horticulturalists have taken a large piece of aluminum foil and cut a slice into it from the center to the outside edge. They then placed this under the plant with the center at the base stem of the squash plant. I’m going to try this in my own garden and I may also try the milk “potion” suggested y. Happy gardening!

    • Tee //

      March 28, 2011 at 7:02 pm // Reply

      Hi John, thanks so much for sharing the trick with the aluminum foil. That’s very interesting. How does the foil prevent powdery mildew? I guess the mildew has some type of reaction with the aluminum?

      Let me know how the milk and baking soda works for you! It does wonders for preventing and control powdery mildew here.

      Thanks for your comment and have a great day!

      • Benji //

        May 26, 2012 at 4:39 pm // Reply

        I’ve heard of this as a control for squash bugs. The light reflected from the aluminum foil disorients the bugs and makes the plants undesirable places to live. I don’t think it’s a fungus control.

  2. Will Metcalf //

    May 30, 2011 at 2:00 pm // Reply

    Going to try the milky spray on my pumpkins and will report back on it’s efficacy.

  3. Brad in Michigan //

    June 17, 2011 at 11:35 pm // Reply

    First time veggie gardener here….I started to notice some powdery mildew on our pickling cucumber plants and have found many internet success stories from using just the 9:1 water to milk ratio so I am going to give it a try and see how it works. We also have lots of squash and zucchini plants so I want to keep it from spreading to those as well! Thanks so much Tee for an awesome and informative site!

    • Tee //

      June 18, 2011 at 9:37 am // Reply

      Hi Brad – Sorry to hear about the powdery mildew. The milk & baking soda spray has worked well in my garden. Just make sure you apply it in the early morning over in the afternoon or evening. Let me know how it works for you!

      • Teresa //

        June 10, 2014 at 10:00 am // Reply

        What should the sprayer be set on 1 tsp.?

  4. Emily //

    June 19, 2011 at 3:47 pm // Reply

    How often should this be sprayed? Thanks.

    • Tee //

      July 1, 2011 at 10:08 am // Reply

      Hi Emily – Once per week at the most. Seven to ten days is best 🙂

  5. Charlie Crab //

    June 30, 2011 at 7:23 pm // Reply

    Hi I have Powdery mildew on my Cucumbers, I live in the tropics of North Qld Australia, I will try the milk and report back

  6. Brad in Michigan //

    July 1, 2011 at 9:35 am // Reply

    Hi Tee! It has been a couple of weeks now and I have done a few applications using just milk and water at about a 25% milk concentration and it seems to be working. The mildew does not seem to be spreading any further and some of the leaves that only had a little mildew on them seem to have cleared up. A few of the leaves that were pretty far gone ended up shrivelling up so I just trimmed them off. I’ll keep ya posted…. thank you for all of your work on your sites to help us amateurs out! Much appreciated!

    • Tee //

      July 1, 2011 at 10:13 am // Reply

      Hi Brad – I’m glad the spray has helped your plants! Yes, the leaves that have a high concentration of mildew should be trimmed. The spray, or anything else, will not help them once they get to a certain point.

      Good luck and have a great day!

  7. Norma //

    July 20, 2011 at 3:46 pm // Reply

    Last year it was squash bugs, this year it’s mildew. I’m gonna’ try this.

    Norma from Idaho

    • Tee //

      July 20, 2011 at 3:59 pm // Reply

      Hi Norma – This spray has helped quite a bit for powdery mildew in my garden. Make sure you only apply the spray in the early morning before the sun rises.

      Good luck and let me know how it works for you!

  8. Wally //

    July 25, 2011 at 4:08 pm // Reply

    Is the fungus dangerous to other things. Can I feed the infected vegetation to my chickens?

    • Tee //

      July 25, 2011 at 5:04 pm // Reply

      Hi Wally – Very good question. The short answer is ….. I have no clue. I don’t think the mildew would hurt the chickens, but if given a large amount, I’m not sure. A little here and there might be OK, but I’d be hesitant about giving them leaves that are covered in it.

      • Fungidude //

        August 26, 2011 at 11:00 am // Reply

        Parasitic fungi are very host specific if it is a plant pathogen it will not harm your chickens. Thanks for the milk tips guys I’m going to try it out this week.

  9. TJ //

    July 29, 2011 at 7:03 pm // Reply

    I have had mildew and squash bug issues for years inspite of rotation as far away as 100 feet. This year I used this mixture but got it wrong with the portion of baking soda. I burned the leaves badly. Since then I corrected the formula and the plants have shed or I have removed all the leaves over time. The plants didn’t start producing until recently but they are doing great now. I treat them weekly, no sign of mildew. As far as squash bugs, without DAILY egg and bug searching, it seems hopeless. Still waiting for someone to post the magic bullet for these pests. I am going to try to put at least a teaspoon of b.soda in my compost tea foliar application to keep the ph to alakline.

    • Tee //

      July 30, 2011 at 2:17 pm // Reply

      Hi TJ – Squash bugs are very difficult to treat. The best thing I can offer is to diligently check the bottom of the leaves for squash bug eggs and to use a spray called Pyrethrin. Pyrethrin is derived from a plant and safe to use on veggies.

      Did the formula I gave above cause your leaves to burn, or was it some other formula? It is also a good idea to only apply it during the cooler morning hours. Never apply it in the heat of the day. Early morning on a cloudy day is ideal.

  10. Norma //

    August 2, 2011 at 10:40 pm // Reply

    Hi Tee – It’s been a little over a week since I tried the milk solution. I’m happy to report that the one squash plant that I was ready to pull has lots of green leaves and two little crooknecked squash. I’ll be armed for next year.

    New problem…the winter squash I plated has lots of flowers each day but has yet to produce any fruit. I haven’t seen any bees around since the first part of the summer. Do you suppose that’s the problem? I’ve taken it upon myself to transfer pollen via a plant brush. Any suggestions?

    • Tee //

      August 3, 2011 at 11:08 am // Reply

      Hi Norma – I’m very glad to hear your squash are doing better! I hope you enjoy your upcoming crookneck squash.

      It definitely sounds like a pollination issue with your winter squash. If there are no pollinators visiting your blooms you may need to resort to hand pollinating them.

  11. Ray //

    August 6, 2011 at 10:44 am // Reply

    Tee, When using hose end sprayer, are you filling the rest of the jar with water or just using that concentrate and letting the sprayer mix the water? Thanks for all your work.

    Ray

    • Tee //

      August 6, 2011 at 12:56 pm // Reply

      Hi Ray – I fill the jar with the milk (plus baking soda and a drop of dish detergent) and ley the sprayer mix in the water. There are many different hose end sprayers and the settings can be different on different models. I usually start out with the sprayer set to the middle setting. There are some that give the option to set ounces per gallon. If you have one of those then I start with the 2 ounces per gallon then adjust as needed. You can set it to the max setting (usually 8 ounces per gallon), but you need to reduce the amount of baking soda by about half. This has worked well for me in the past.

  12. Norma //

    August 6, 2011 at 1:36 pm // Reply

    Forgot to mention that I painted the solution on the leaves. I only have three squash plants and it was easy to do.

    I’ve bookmarked your site and have referred to it for several other plants and plant issues. Thanks!

    • Tee //

      August 7, 2011 at 12:15 pm // Reply

      Hi Norma – That’s a very interesting way of applying the solution. I’ve never tried that before. I’m glad it had worked well for you. Thanks for sharing your experience!

  13. Scott Estell //

    August 19, 2011 at 4:29 am // Reply

    I have used the Copper Sulfate solution in the past. It is sooo expensive but it works. Especially when it rains & you have to re-apply. Our Squash,Pumps & Cukes have it now real bad. I will give your Milk/soda solution a try. I’ll report back in a few weeks. Wish us luck

  14. Barry //

    August 19, 2011 at 11:01 pm // Reply

    Just discouvered your site while looking for powdery mildew solutions on my squash and cucumbers, first application was today. I will keep you posted.

    Thanks for the info and a great site

    British Columbia

  15. Mary //

    August 22, 2011 at 7:44 pm // Reply

    Hi – I have a terrible problem with powdery mildew on my summer squash and pumpkins. Glad I found your site! I will try the milk solution. I removed a LOT of leaves last night. There were new little leaves coming up beneath them, so hopefully those will take over soon and the plant won’t be too stressed from all the pruning. It seemed like a LOT of pruning! Mary in Los Angeles.

    • Tee //

      August 22, 2011 at 9:50 pm // Reply

      Hi Mary – Removing the infected leaves is an excellent idea. They need to be removed to decrease the rate of spreading. Let me know how the milk/baking soda spray works for you!

  16. T.J. //

    August 27, 2011 at 8:19 am // Reply

    When removing squash leaves, how much,if any, of the long stem should be removed?

    • Tee //

      August 27, 2011 at 9:07 am // Reply

      Hi T.J. – If you are removing some leaves from the squash plant you can remove the stem all the way to the main stem it branches off of. It will not re-grow a new leaf so you can remove it.

  17. Helen //

    September 4, 2011 at 2:41 am // Reply

    I just found powdery mildew on my crooked neck squash. I am in NW Oregon. I will try your treatment and remove the existing disease leaves. I planted my pumpkin, summer & winter squashes too close together! Should I pretreat the whole bunch of it or just the ones showing powdery mildew? Will my zucchini get this too? Thanks and I will let youknow how it works.

    • Tee //

      September 4, 2011 at 7:30 am // Reply

      Hi Helen – Yes, you can pre-treat your other plants to prevent them from getting powdery mildew, but I would reduce the amount of baking soda by half for those plants. Zucchini can get powdery mildew too.

  18. Jesse //

    September 11, 2011 at 4:16 am // Reply

    Got powdery mildew on my pepper and tomato plant. Removed quite a few leaves, but I’m going to try the 9:1 (water/milk) milk, today.

    Heat, snails, and now powdery mildew are crushing my vegetables.

  19. Carrie //

    September 11, 2011 at 2:33 pm // Reply

    I am a first time gardener in Souther Californina and I have powdery mildew on my pumpkins and yellow crockneck squash. I will be trying the milk solution and trimming the infected leaves. In the meantime, is the fruit that is ripening now still edible?

    • Tee //

      September 12, 2011 at 11:57 am // Reply

      Hi Carrie – Good luck with treating the powdery mildew. Let me know if you have any issues and also your successes. The fruit are still very edible. The mildew affects the plant itself and not the fruit. Keep in mind there are mildews that can affect the fruit but not powdery mildew.

  20. Alfred //

    September 12, 2011 at 10:22 pm // Reply

    Does the powdery mildew on my Lil’Pump-Ke-Mon winter over? Are there things I should do to prevent a reoccurrence next year?

    Thanks if anyone has the answers.

  21. Becky //

    September 14, 2011 at 9:00 pm // Reply

    Hi Tee,

    Just to let you know – we had this problem in mid August and used your solution – – of course we put it on at the end of the day (ooops!) and we did cut back the infected leaves – worked like a charm. Now I am going to reapply (in the morning tomorrow!) as I see today some spots coming back on the one squash that was infected. It never spread to anything else, but I guess that is because we removed the worst leaves and sprayed the whole plant and the other plants as well. THANKS! This WORKS!

  22. Dana //

    September 24, 2011 at 11:54 pm // Reply

    Hi Tee,
    Despite my best attempts, powdery mildew has taken over my entire pumpkin plants. However, I do have 3 fairly good sized pumpkins. One is mostly orange but the other two are quite green. Should I pick them now even though it is a month before Halloween? The pumpkin vines look quite shriveled and I don’t think they are getting much nutrients. I have read on some other sites about treating them with a 10% bleach solution and putting them in the sun so they will hopefully turn orange and not rot. What do you suggest? We live in Denver, CO so the climate is fairly dry. I was also wondering if I should treat the soil over the winter to avoid getting PM and if so with what?
    Thanks so much for taking the time to make this great website,
    Dana

  23. Mehr //

    March 25, 2012 at 10:24 am // Reply

    Hi Tee, My garden was taken over by the powdery mildew last yea. I wish I had know about milk remedy. Now I am ready to start the garden for this year but I am afraid that the soil is contaminated with the left over infected cucumber plants from last year. Is there any way for me to treat the soil before bringing the new plants in?

    • L //

      July 22, 2012 at 5:30 pm // Reply

      I was hoping for an answer to your question about the soil because I’ve been worrying about that, too! I just moved to the running up Rain City in the country, and didn’t know what was happening (this mildew) until it was way too late. I am digging up many flowers and throwing them away, but am very paranoid now about my tools and soil. I’m also wondering if I can rescue some root systems of plants that were so moldy. I tried digging up a few, washed them in the home-made fungicide (using a different recipe-just found this site), base (threw entire stem system away) and roots, rinsed with water, and then re-potted in loose soil. I did not put them back in the ground yet, since I don’t know what to do about all that dirt. Well, I suspect I should just throw it away anyway, because my guess is that it’s too clayish for this climate, and I need to replace it all with some sand/soil combo for great drainage (?). But the contamination thing has me paranoid, too. Thoughts?

  24. Renee //

    May 16, 2012 at 8:18 am // Reply

    I am going to try the milk and baking soda solution…..I lost my first crop of yellow squash and zuccini and cucumbers to this molding on the leaves, everything was fine then BAM the veggies started and fell off and the plant died. Re-planted soon after but in a different spot, thanks for the tip i will try it and let you know how it worked. Thanks again.

  25. Anonymous //

    June 15, 2012 at 8:12 am // Reply

    Be careful about the baking soda. It helped the first couple of times, then somehow my winter squash plants started “burning” with a reddish splatter pattern even though the concentration was similar. I rinsed the plants as soon as I observed damage, but the spots turned white over the next few days as soon as bright sun came out. I am trying the milk solution instead. I have used a 1:4 milk spray twice in the last week but it rains every day, and the mildew is getting worse. I have not had issues with powdery mildew on these plants except when it rains multiple days and the temperature hovers in the 80s, it seems to have a hard time surviving multiple full sun days of 90 degrees with only water to the roots of the plant. It is getting to the point where there are so many slightly infected leaves it would hurt the plant to remove them.

  26. Mew //

    July 1, 2012 at 7:55 pm // Reply

    Hello Tee,

    I used only baking soda on my plants and they starts burn right away. I want to try your recipe, but I have a very small garden. I am wondering if I can use spray bottle instead of using sprayer.

  27. SueD //

    July 25, 2012 at 9:04 pm // Reply

    I tried this remedy on my pickling cukes and it worked like a charm! Thank you, Thank you! I thought I was going to lose the whole crop.

    I do not have a hose end sprayer as mentioned above so I used this recipe: In a 32 oz container, mix 2/3 cup milk (I used 1%), 1 tsp of baking soda and 1 drop dish detergent. I topped the container off with water and applied to the leaves using a spray bottle. I removed the most badly affected leaves and sprayed all the rest with the solution and it cleaned it right up. I reapplied after a rainstorm a few days later.

  28. Brandie //

    July 26, 2012 at 12:25 pm // Reply

    Thank you all so much for your comments. Just finished pruning newly infected leaves and I plan on applying the baking soda/milk/dishsoap potion tomorrow am. I used milk only last year with so-so results. I’m guessing the baking soda is the magic ingredient. I also read that crushed garlic in the solution helps. Any thoughts?

    Any idea if it’s ok to mix the potion in with my fish emulsion foliar spray? I have one that is plain fish oil and one that has sesame oil in it, which I was guessing might help everything to coat the leaves longer.

    We’re expecting on heck of a storm today, so hopefully I’ll have plants left to tend!

  29. CS Zheng //

    July 27, 2012 at 3:51 pm // Reply

    Hi Tee,

    According to your recipe, how much water needed if I use a Chapin RB2000 pressure sprayer to spray?

    Regards.

  30. Barbara //

    August 3, 2012 at 12:53 pm // Reply

    Two questions:
    1. is the fruit from the squash that is infected with powdery mildew still edible?
    2. is this a problem that lives in the soil, or can I try again in the same spot next year?

    • jean //

      January 10, 2015 at 5:51 pm // Reply

      It’s best not to plant the same crop in the same spot for at least three years. Crop rotation helps prevent pests and disease.

  31. ann //

    August 6, 2012 at 6:58 pm // Reply

    I want to try the milk and baking soda treatment as a last resort for zuchini and summer squash plants that are heavily infected with powdery mildew. Can this be done during extreme high temperatures? Our daytime highs are and will be around 100 for the near future.

    Thanks, ann

  32. Kristy //

    June 14, 2014 at 8:54 am // Reply

    Hello there. I’m growing my very first pumpkin plant and I was having some problems. After visiting your site, I now believe it’s powdery mildew. So, I made the mixture and sprayed it on my plant… and then I realized that I didn’t put any water in the mix. Did I just unknowingly damage my plant?

  33. Rocky //

    August 8, 2014 at 4:46 pm // Reply

    HI Fellow gardners.
    I had powdery mildew on my zucs pumpkins and all my mellons. Mixed 2 table spoons of dish detergent 4 Tbls baking soda and 1 gallon of water. first three days of treatment spors and white marks went away. now its only spotty. Some leaves were burning so now I use this next mixture. I now mix 2 drops of dish detergent 2 table spoons of baking soda and a gallon of water and sprayed everything for the next 7 days early in the day. a few leaves died 80% of my leaves were saved. As stuff burned up or died I trimmed it off thru it in the out bound garbage can sealed away from the garden. I am now using the above mixture and I add the
    25% milk spraying the melon garden down once a week. and its saved my crop. everything is green. Thanks so much to all of you. It saved my season. Plus those little yellow lady bugs with black spots hate the mix and left. So far.
    So thanks a ton i am very grateful.

  34. daver //

    August 8, 2014 at 6:42 pm // Reply

    I have the powder problem with my squash and mellons. Will try your solution.
    I have a comment on John SSchoolers comment about aluminum foil. Couple years ago I read in Mother Earth to put foil under plants – the reflected sunlight frightens off the little white butter flies that lay eggs at the base of the plants. This is to prevent the larva that bores into the root and cases the plant to collapse overnight.

  35. Taunya //

    November 1, 2014 at 9:58 pm // Reply

    How much milk for a 2gallon sprayer? I have a problem with the powdery mildew here in central Missouri

  36. jean //

    January 10, 2015 at 5:53 pm // Reply

    I don’t understand why people are mixing baking soda in with the milk and water and risking burning their plants when the published study showed that milk and water alone were effective. To each his or her own, but it doesn’t make a lot of sense to me.

  37. Denise //

    April 13, 2015 at 9:52 am // Reply

    I sprinkle Epson salt around the cuc plants before it rains to get into the root system before any evidence of mildew – someone’s grandma said it worked, and it does. Reapply after 3-4 weeks.
    No one gave any suggestions for what to put into the soil prior to tilling and planting. Anyone try lime?

  38. Carol //

    May 4, 2015 at 5:05 pm // Reply

    Last fall it was squash bugs, this spring it is fungus-mildew. have it on my squash plants and gourds. Can not wait to try this solution starting in the morning. I live in the south and my plants were doing wonderful until we had 3 straight days non stop rain, day and night. I knew my plants were in trouble. I try to water them using a soaker hose so the leaves don’t get wet. But knock on wood so far no squash bugs on anything, Will let you know how it turns out. Thanks again.

  39. Kim Kosin //

    June 13, 2015 at 8:26 pm // Reply

    Hi John,

    I recently transplanted two summer squash plants. They have developed what I believe is powdery mildew. They are very small with only a couple of leaves. You mentioned to trim off the affected leaves, but if I do that I may not have any leaves left. Does this mean I should discard the plants? The leaves seem affected everywhere. Thanks!

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Organic Ways to Kill and Prevent White Powdery Mildew

Updated on July 23, 2018

Gcrhoads64 profile image
Gable Rhoads

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Gable loves to surround herself with plants year round, and as a former landscaper, she has seen a lot of plant diseases.

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What Is This Powdery Mildew on My Plants’ Leaves?

As a former landscaper, I have seen a lot of plant diseases. One of the easiest ones to recognize is powdery mildew; it looks just like its name. The mildew will form a white or gray powdery film on a plant’s leaves, stems, and fruit.

Powdery mildew is a fungal disease caused by the many varieties of the fungi that belong to the order Erysiphales. The fungus thrives in warm, humid environments, and overwinters in the soil. The mildew forms spores that spread through wind, insects, and water run-off, which carries the disease to other plants. According to the Arizona Cooperative Extension, “Unlike most fungi, spores germinate on the surface of plant parts without the presence of free water.”

Note

•When treating your plants, make sure the leaves are coated liberally with the solution.

•Reapply weekly unless otherwise specified on a product’s label.

8 Organic Treatments to Get Rid of Powdery Mildew

  1. Potassium bicarbonate
  2. Milk
  3. Neem oil
  4. Vingar
  5. Baking soda
  6. Garlic
  7. Sulfer
  8. Copper fungicides

1. Potassium Bicarbonate

Potassium bicarbonate is a safe, effective fungicide that kills spores on contact. Like baking soda, it is also a great preventative treatment because it raises the pH level above 8.3—an alkaline environment that is not ideal for fungal growth.

How to Use:

Mix 3 tbsp. of potassium bicarbonate, 3 tbsp. vegetable oil, and 1/2 tsp. soap into a gallon of water. Spray onto affected plants.

2. Milk

Numerous studies have shown milk and/or whey to be even more effective at killing powdery mildew than chemical fungicides. In a 2009 study by the University of Connecticut , which tested a milk treatment of 40% milk and 60% water on plants infected with powdery mildew, “the milk treatment provided significantly less disease than the untreated control, and the chemical treatment had equal or significantly less disease than the milk.” Scientists are not sure why milk is so effective, but they believe that when milk interacts with the sun, it produces free radicals that are toxic to the fungus .

2 Ways to Use:

  • Mix 60 parts water with 40 parts milk or whey, and spray onto the affected plants bi-weekly. You can even use whole milk without dilution for a strong effect.
  • Mix 1 oz. powdered milk to 2 liters of water, and spray onto affected plants bi-weekly.
Milk may be more effective at killing powdery mildew than even chemical products.
Milk may be more effective at killing powdery mildew than even chemical products.

3. Neem Oil

Neem oil is made from the seeds and fruit of the evergreen neem tree, and it is powerful enough to kill powdery mildew in less than 24 hours. The oil works by disrupting the plant’s metabolism and stopping spore production. Neem oil is also a great insecticide and since spores can be carried by bugs, this oil is a great preventative treatment as well.

How to Use:

Mix 3 tbsp. of neem oil to one gallon of water, and spray onto affected plants every 7-14 days. Take precautions to avoid sunburning the leaves, and avoid spraying the plant’s buds and flowers.

4. Vinegar

The acetic acid in apple cider vinegar is very effective in killing powdery mildew. Take care to not make the mixture too strong as the acidity of the vinegar can burn plant leaves.

Mix 4 tbsp. of vinegar (5% solution) with 1 gallon of water. Reapply every three days.

5. Baking Soda

Baking soda has a pH of 9, which is very high! Treating with baking soda raises the pH level on the plants and creates a very alkaline environment that kills fungus. There have been mixed reports of success when using baking soda to treat severe cases, so it may be better as a preventative treatment than a fungicide.

How to Use:

  1. Mix 1 tbsp. of baking soda and 1/2 tsp. liquid hand soap with one gallon of water.
  2. Spray solution on affected leaves, and dispose of any remaining solution.
  3. Do not apply during daylight hours. It may be best to test one or two leaves to see if the solution will cause the plant to suffer sunburn.
Baking soda's high pH creates a high alkaline environment that is unsuitable for fungi.
Baking soda’s high pH creates a high alkaline environment that is unsuitable for fungi.

6. Garlic

Garlic has a high sulfur content and is an effective anti-fungicide. Garlic oil can be bought commercially if you do not wish to make the solution at home. It works best when added to organic oil mixtures.

How to Use:

  1. Crush six cloves of garlic and add to one ounce of an organic oil such as neem oil and one ounce of rubbing alcohol. Let set for two days
  2. Strain and retain the liquid and crushed garlic.
  3. Soak the garlic again (this time in one cup of water for a day). Strain out and dispose of the crushed garlic.
  4. Add the oil and alcohol mixture and garlic water to one gallon of water.
  5. Spray your plants, coating only the leaves.

7. Sulfur

Sulfur is a natural product that is very effective at preventing and controlling powdery mildew. Sulfur can be bought as a dust or as a liquid and can be added to sulfur vaporizers.

How to Use:

Follow the dosing instructions closely and wear gloves, eye protection, and a face mask. Avoid inhaling or coming into contact with the sulfur.

8. Copper Fungicides

Copper is a very effective fungicide, but it is very important to follow label directions closely. Too much copper will be detrimental to the plant and the soil.

Warning

Some ingredients, such as vinegar and baking soda, can cause sunburn to your plants. Ensure that plants are well-watered before applying and don’t apply during daylight hours.

Powdery mildew on poinsettia plant.
Powdery mildew on poinsettia plant. | Source

How Can I Prevent Powdery Mildew?

Preventing the spread and/or severity of powdery mildew is the most cost-effective way of dealing with the fungus. Powdery mildew thrives in temperatures 50-65 degrees Fahrenheit with humidity levels of 80-90 percent. To prevent powdery mildew from forming in the first place, avoid low-temperature, high-humidity environments.

Do Not Crowd Plants

Good air circulation ensures lower humidity levels, inhibiting the growth of powdery mildew. Crowded plants also provides too much shade for the lower leaves, which encourages fungi growth.

Do Not Grow Susceptible Plants in the Shade

Powdery mildew does not tolerate high temperatures. Direct sunlight helps stem the growth of mildew because the sun’s strong rays kill spores before they can spread. Plants that are shaded much of the day will stay cooler, thus encouraging the growth of mildew.

Dispose of Infected Leaves and Stems

Never use infected plant leaves or fruit as mulch or compost. Trim off infected leaves and stems and dispose of them properly. If your municipality allows backyard fires, then burn the debris. If not, dispose of the debris according to your local plant disposal regulations.

Water the Soil, Not the Plants

While water itself will not encourage mildew growth, splashing the leaves with water will spread the spores. Run a hose to the base of your plants instead of using a sprinkler system.

Buy Mildew-Resistant Varieties

There are a large variety of hybrid plants that are resistant or tolerant to the growth of powdery mildew. The resistant plants will be less likely to develop the mildew. The tolerant plants will show fewer ill-effects of an infestation of the fungi.

Powdery mildew on pumpkin leaves,
Powdery mildew on pumpkin leaves, | Source

Plants and Vegetables Most Susceptible to Powdery Mildew

Lilacs
Phlox
Roses
Begonias
Sunflowers
Dahlias
Zinnias
Chrysanthemums
Cucumbers
Grapes
Squash
Apples
Melons
Lettuce
Parsley
Tomatos
Peppers
Zucchinis

Are All Forms of This Fungus the Same?

There are many forms of powdery mildew, and each is species specific. Grapes will suffer from the powdery mildew that affects only grapes, roses suffer from rose powdery mildew, and so on.

Although all plants can get the fungus, certain species are more susceptible to it. If your plant has a black sooty substance on its leaves, it may be sooty mold .

Where Does Powdery Mildew Start?

The mildew usually starts on a plant’s lower leaves, and if the fungus is not treated it will spread over the entire plant. When the leaves become severely covered with the fungus, photosynthesis will be affected and leaves will yellow and drop off. As a result, the plant may become so stressed it will not flower and/or fruit with any vigor.

For More Information

  • Powdery Mildew
    Most powdery mildews are recognized by the white to gray,
    powdery spots or large blotches on the surface of leaves,
    stems and fruits of host plants. T

Questions & Answers

  • I discovered powdery mold on my cucumber plants today. I’ve already picked seven of them. Many have already started. Will this kill the ones that are started?

    No, but powdery mildew can affect the growth and vigor of the cucumber plant. Treat the powdery mildew now, and then weekly until the fungus is gone.

    Helpful 26
  • Can I still wash and use the cucumbers if a plant has signs of Powdery mildew?

    Unless you have an allergy to the fungal spores, washing it would make it safe to eat, although if the cucumbers themselves are heavily mildewed, they may taste moldy.

    If there is any doubt, DO NOT eat the fruit as a severe allergic reaction could be fatal.

    Helpful 23
  • What plants (shrubs) are resistant to powdery mildew fungus?

    There are many varieties of shrubs bred to be resistant to powdery mildew. If you know what shrubs you want, research which varieties are available, or ask your local nursery or local county extension agent which varieties are good for your climate.

    Helpful 4
  • Can I treat the soil before I replace the current plant with a new shrub?

    You can, but the mildew spores do not reside in the soil. Remove any plant debris from an infected plant from the area and dispose of. If you are having a chronic problem with mildew, ensure you have adequate circulation between plants, and water plants at ground level to avoid spreading the spores. Also look to see if there is enough natural sunlight, which helps control the growth of the mildew.

    Helpful 19
  • How often should I apply baking soda spray to kill mildew?

    Reapply once a week, or after a heavy rain.

    Helpful 16
show more
  • Will a weak solution of bleach and water kill powdery mildew on lilac leaves?

    Yes, it will, but I would make the solution very diluted and test it on one leaf first. Do not drench the leaves or soil with the mixture.

    Helpful 14
  • I’m effectively using the baking soda solution in my vineyard this year to prevent white powdery mildew, though I am a bit concerned. Will it have a negative effect in making the wine? There is a slight film on the grapes now. We will harvest within the next 30 days.

    Just wash the grapes well before making wine. The baking soda film will easily wash off the grapes, and will not penetrate the thick skin of the fruit.

    Helpful 8
  • I have kale with powdery mildew. Is it safe to eat the leaves if I wash them well?

    Most people have no problem…
    Helpful
  • Can I reuse the soil after it has been treated for powdery mildew?

    Yes, but I would either pretreat the soil or otherwise sterilize it.

    Helpful 3
  • We grow vine leaves for making dolma to eat. Which treatment would be most effective?

    I would use the neem oil on your leaves. Remember to wash leaves well before consuming.

    Helpful 3
  • Can I treat the soil prior to planting to prohibit the mildew from growing?

    Yes, you can. There are several ways to do this.

    Terraclor, Iprodione, and Mefenoxam are examples of chemicals that can treat the soil. Check the labels to see what fungi it controls and how to apply.

    Some organic gardeners pretreat large gardens areas by heavily soaking the ground with water, then covering the garden area for 4-6 months. The heat and humidity kill spores as well as weeds.

    Helpful 2
  • Do you treat small houseplants the same way?

    Yes, houseplants can be treated the same way. I would suggest treating the plant and changing the soil.

    Helpful 2
  • My mango tree is a sapling and has powdery mold. How should I treat it?

    Cut off the affected leaves and remove any diseased fruit or blossoms. Remove the infected plant parts as the fungus can still be carried to healthy parts of the plant.

    Spray with any of the products mentioned in my article, concentrating on the leaves and their undersides; repeat every two weeks. In the spring, a preventive spraying will reduce fruit loss.

    Helpful 2

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Comments


  • profile image

    Suzie HQ 

    3 weeks ago

    Thanks for a really interesting article and I am all for organic solutions. At present I find a number of plants in your list in need of some treatment. I am living in Southern Italy where high summer temps and high humidity play havoc with plants on one hand and give amazing growth on the other. I have a big sunflower plant in a container with about 80 flowers quite a showpiece but it does seem to have alot of mildew . I have tried your vinegar recipe so fingers crossed! Many thanks again I will be saving and using it again.

  • profile image

    Paula 

    2 months ago

    …ive had this powdery on my houseplants…ive been

    using…an organic purchased product..doesnt seem to do the job..i love baking soda/vinegar..gt products 4 many uses..i will try this..and also milk..thanku

  • chris nddie profile image

    Chris Nddie 

    2 months ago from Dana Point

    Organic is Natural else all are Chemicalize. Great post

  • profile image

    Doug 

    3 months ago

    Thanks for this article, Gable. Great information! I am testing some of the treatments you suggest in my garden.

    As regards using milk to combat powdery mildew, it may be true, as you write, that "Numerous studies have shown milk and/or whey to be even more effective at killing powdery mildew than chemical fungicides." That is not true of the study you cite, however.

    That paper compared milk treatment to chemical treatment at two outdoor locations (Storrs field and Windsor) and concluded that "Storrs field showed milk was as effective as the chemical control [chlorothalonil)]….At the Windsor location, however, the milk treatment was not as effective as the chemical control."

    The study also compared milk to chlorothalonil in a greenhouse environment and found that "the milk and chemical treatments… did not differ from one another…in their effectiveness."

    The very good news for organic gardeners is that this study found milk to be very effective: just as good as the chemical fungicide at two out of three test sites! It did not find, however, that milk is "even more effective…than chemical fungicides."

  • Gcrhoads64 profile imageAUTHOR

    Gable Rhoads 

    4 months ago from North Dakota

    Typically the leaves do die because of the infection. Remove them to stop the spread of any spores which may still be living. As to the entire plant dying, it could be the result of a very bad case of powdery mildew or many other causes. It may be best to start over with new plants and soil.

  • profile image

    Alex tesfaye 

    4 months ago

    The powdery mildew reduced. But now i have much problem the leaf of the sage curl upward and turn in to brown and the plants are dying

  • Gcrhoads64 profile imageAUTHOR

    Gable Rhoads 

    5 months ago from North Dakota

    Alex, neem oil is an organic substance. Do you continue to have powdery mildew after spraying?

  • profile image

    Alex tesfaye 

    5 months ago

    I am interested in agriculture field in Production of vegetables, fruit and herb. And i have problems with powdery mildew my sage plant. I am growing them organic. I spray neem oil but it is the same?

  • profile image

    Anne H 

    8 months ago

    What is this “Mitey sauce “you speak of? Coconut oil?

  • profile image

    Patricia Bagshaw 

    12 months ago

    Wonderful article. My plants have stunted growth. No blossoms. Geraniums have very small leaves and no flowers. I water and fertilize so I am not sure what my

    Problem is. Thank you.

  • profile image

    Jasmine Flower 

    13 months ago

    That is a really good idea John.

  • profile image

    John 

    15 months ago

    Try "mitey sauce" a local company- the coconut oil in it works on Powdery mildew but does not block the stomata like neem oil does.

  • Gcrhoads64 profile imageAUTHOR

    Gable Rhoads 

    15 months ago from North Dakota

    Liz, according to this website, the rosemary is safe to eat: https://extension.umd.edu/growit/downy-mildew-basi…

    Other sites say it may affect the flavor. If you are treating the plants, wash the leaves thoroughly.

  • profile image

    Liz 

    15 months ago

    I have some on my rosemary plant, what happens if I eat it?

  • profile image

    Carmine 

    15 months ago

    I think if powdery mildew on grapes turns the skin dark color and some skins crack it is too late those clusters should be cut off and discarded i trash bin. Then the infected vines should be sprayed with one of the articles recommended materials

  • profile image

    Vishal 

    18 months ago

    In India Maharashtra the powdery mildew have largely affected grapes…

  • profile image

    Mike 

    2 years ago

    Fist site I found that gave the when to reapply info. Thanks.

  • Gcrhoads64 profile imageAUTHOR

    Gable Rhoads 

    2 years ago from North Dakota

    Thanks for the comments Kristen and breathing. It is encouraging to get positive feedback. 🙂

  • breathing profile image

    Sajib 

    2 years ago from Bangladesh

    Plant lovers will be greatly benefited from this post. Indeed plants are subjected to many diseases. Powdery mildew is a very common disease among the plants. Many people who have their own plants don’t know how to treat powdery mildew. This post can be the cornerstone for them. The steps described in this hub are really worthwhile. I’ve tried a few ones myself and find them to be really effective. The organic ways are very much helpful. That’s why I advise the plant lovers to use the teachings of this post to exterminate powdery mildew. Also none of the processes are costly.

  • Kristen Howe profile image

    Kristen Howe 

    3 years ago from Northeast Ohio

    Great hub, Gable. This is so useful to know for next season, when I watch over my container garden. I’ll keep it in mind to use milk or baking soda, if I do have that powdery mildew on my plants. Two green thumbs up!

  • profile image

    JANARDHAN N 

    4 years ago

    this as given me some assistance to fight against powdery mildew

    thanks to rentokil

  • Gcrhoads64 profile imageAUTHOR

    Gable Rhoads 

    5 years ago from North Dakota

    I’m glad I could help. 🙂

  • RTalloni profile image

    RTalloni 

    5 years ago from the short journey

    Thanks for this helpful look at eliminating powdery mildew from plants. I have one that needs attention…

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