Controlling or Eliminating Powdery Mildew

Providing adequate air circulation will help avoid powdery  mildew in your garden

Judging from the number of questions I get every summer about the plant fungus known as powdery mildew, I’ve learned three things over the years; it’s everywhere, you don’t like it and you want to know how to get rid of it. So, here’s what you need to know to prevent, control and even eliminate it after it appears.

You’re not alone

Powdery mildew is one of the most widespread and easily identifiable plant fungal diseases. From vegetable gardens to rose gardens, ornamental trees and shrubs, almost no type of plant is immune.

If you find that some of your plants or trees have powdery mildew, don’t worry. This fungus is host specific, meaning just because you find it on one plant species, does not make it a threat to other type plants in your landscape. Although there are many different species of powdery mildew, the symptoms all look about the same from one to another.

What to look for

You’ve likely seen it many times. White or gray powdery spots appear, often times covering most if not the entire leaf surface. It’s also found on plant stems, flowers and even fruit. Fortunately, the symptoms of powdery mildew are usually worse than the actual damage. Rarely is it fatal to the plant.

Advanced stages can cause plant foliage to yellow, curl or turn brown and eventually cause the plant to defoliate prematurely. On flowering plants and trees, the fungus can lead to early bud drop or reduce the flower quality.

So Now What?

Conditions that favor mildew formation include dry foliage, high humidity, low light and moderate temperatures. Proactive steps to avoid or minimize this risk include:

· Look for disease resistant varieties. Contact your local county extension service for named varieties and cultivars.

· Provide adequate air circulation by not crowding plants.

· Site plants where they will get sufficient light of six hours or more each day. Minimize shade and trim trees and shrubs that block the light.

· Avoid over fertilization. New growth is more susceptible. Instead, apply a slow-release fertilizer that provides more controlled growth.

Controlling an existing problem

Should you find the need to react to an existing condition of powdery mildew, early detection provides the best way to contain and potentially eliminate the problem. There are many commercial products that are effective at containing the spread. However, eliminating an existing problem is not a given.

Most conventional products are made for prevention and control, not elimination of an existing infection. That’s why it’s important to start a control program before powdery mildew occurs or at least at the earliest sign of detection.

There are many retail, off-the-shelf fungicide products that are effective at treating mildew. One of the most common active ingredients used for control is “chlorothalonil”. Although effective, it coats the leaf surface with a white milky film that is quite noticeable.

Lesser know options include:

Baking Soda (sodium bicarbonate) -This is possibly the best known of the home-made, organic solutions for powdery mildew. Although studies indicate that baking soda alone is not all that effective, when combined with horticultural grade or dormant oil and liquid soap, efficacy is very good if applied in the early stages or before an outbreak occurs.

Use this recipe to make your own solution—mix one tablespoon of baking soda with a teaspoon of dormant oil and one teaspoon of insecticidal or liquid soap (not detergent) to a gallon of water. Spray on plants every one to two weeks.

Potassium bicarbonate– Similar to baking soda, this has the unique advantage of actually eliminating powdery mildew once it’s there. Potassium bicarbonate is a contact fungicide which kills the powdery mildew spores quickly. In addition, it’s approved for use in organic growing.

Mouthwash – If it can kill the germs in your mouth, certainly the fungal spores of powdery mildew are no match. And that’s the premise. Generic, ethanol based mouthwash can be very effective at control. Tests using one part mouthwash to three parts water worked for well for Jeff Gillman, Ph.D and Associate Professor at the University of Minnesota, Department of Horticulture. Just be careful when mixing and applying mouthwash as new foliage can be damaged.

Vinegar – Similar to mouthwash, the acetic acid of vinegar can control powdery mildew. A mixture of 2-3 tablespoons of common apple cider vinegar, containing 5% acetic acid mixed with a gallon of water does job. However, too much vinegar can burn plants but at the same time, higher concentrations (above 5%) are more effective.

Sulfur and Lime/Sulfur – Direct contact by sulfur prevents disease spores from developing. When mixed with hydrated lime, the solution will penetrate leaves for even greater effectiveness. A widely available version of this combination includes copper sulphate and hydrated lime, known as Bordeaux mix. However, all of these solutions can burn plant tissue and is damaging to microorganisms in the soil and harmful to beneficial insects. It is also considered moderately toxic to mammals and humans. Use sparingly and with caution if at all.

Milk – The latest player in the fight against powdery mildew is milk. It’s not clear yet why it works so well, but it is believed that naturally occurring compounds in the milk are at work to combat the disease while also boosting the plant’s immune system. One experiment showed good results by applying a weekly dose of one part milk to two parts water.

Water – Ironically, dry conditions and high humidity are the most favorable conditions for powdery mildew to form. But straight water is its enemy because it washes off the spores before they have time to embed. However, water isn’t something that I promote for control because wet foliage is friend to many other plant diseases. If you’re going to try this option, do so early in the day so foliage has time to dry out quickly.

Neem oil – This is a readily available organic option to disease and pest control. Neem oil is extracted from the neem tree, native to India. This is an effective disease control and a broad spectrum, natural insecticide that is kinder to beneficial insects and mammals. As for controlling powdery mildew, results vary but it is not the best option. Results are usually moderate at best.

Even with many choices for control, prevention is still the best medicine, not only with powdery mildew, but with other diseases as well.

6/29/15 Update: Comments are currently turned off for this post due to the volume of questions and answers already included. Please scroll down and you will likely find your question and answer listed below. Thanks!


Joe Lamp'l is the Host and Executive Producer of the award winning PBS television series Growing A Greener World. Off camera, Joe dedicates his time to promoting sustainability through his popular books, Compost Confidential blog, podcast series, and nationally syndicated newspaper columns. Follow Joe on Twitter

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  1. Tim says

    I just wanted to thank you for posting this information. I NEEDED it!

    I’m going to give your suggestions a try. Fortunately, I have access to things like Potassium Carbonate and lime (CaCO3), but I know very little about gardening. Your advice is very helpful. Thank you.

  2. says

    I have a luscious honeysuckle that is a perfect breeding ground for aphids but also ladybugs. It is also a favorite of the hummingbirds.
    Every year the honeysuckle succumbs to powdery mildew.
    My concern with treating the plant is that I will kill the ladybugs (eggs) and harm the hummingbirds.
    Are any of these treatments safe for the ladybugs and hummingbirds?

    • says

      The recipe in this article that mentions milk and water will not harm hummingbirds or beneficial insects. But glad you are concerned about that. I wish more people were.

  3. says

    Hi Joe,
    I’m so happy I finally found the answer to my problem. One question, should I apply for he solution in the morning or afternoon after the heat has cool down? One more thing, I have read somewhere that said mix baking soda and milk. Have you ever try this yet? I just don’t know how much milk and baking soda to mix

    • says

      Kris, I haven’t tried just milk with baking soda. You should try and let us know. As for the time to apply, I think early in the day would be best. That way the leaves get the appropriate coating but the leaves have a chance to dry out quickly from any moisture.

  4. Marsha says

    HELP! You recommend Potassium Bicarbonate for fungus already existing on my garden phlox plants. However, I am having a heck of a time finding it!! Some guy sold me a product called Potash 0-0-60 Soluble Potash (K2O), he said it is the same thing as Potassium Bicarbonate. Is that correct???

    • says

      The formula for Potassium bicarbonate is CHK03, not K20. You can find products that include potassium bicarbonate by typing “potassium bicarbonate fungicide” into your browser. GreenCure was the product I have used with success that is uses this formula.

  5. ali says

    hello joe
    i want to know which ph is perfect for living powdery mildew one of my freinds used sulfuric acid and H2SO4 to control apple powdery mildew is it corect??

    • says

      Hi Ali. I did not know the answer to your question so I asked my “go-to” guy, Jeff Gillman (author, professor, PhD, Horticulturist, etc. etc! Anyway, here’s his reply, and I quote;
      “Run for the hills! This is insane! Sulfuric acid will kill the plant, the powdery mildew, and will scar you if it gets on you. By the way, H2SO4 is sulfuric acid. Use commercial sulfur products to control powdery mildew, not mix it yourself acids.”

      So there you go Ali. Hope this helps.

    • Tim says

      Hi Ali,

      I thought I’d add to what Joe said. I’m a scientist and my second degree is in chemistry. My PhD is in Bio-engineering. I say this only so you’ll know I know what I’m talking about. H2SO4 IS sulfuric acid. It absolutely will kill your plants AND if it touches your skin or clothing, it will burn them. Of course, it could be very dilute so it would only hurt a little but…. Suffice it to say, THAT is not what you want. Potassium Carbonate would be K2(CO3), which you’d have to buy from suppliers of chemical and biological reagents (i.e. Fisher Scientific). It would be expensive to purchase that way. You probably want something like I hope the link shows. Green Cure Fungicide… Good luck with it. I’m having the same problem and it’s killing my Zuchinni and Squash.

  6. Lauren says

    I just found mildew on ever leaf of the zucchini I planted two weeks ago. I realize now, as this is my first garden, that I caused it by watering too much.
    I treated the plants with an over the counter solution and cut away the infected leaves at the base. Now my plants look like stubs with a few new leaves coming in. Was this the right thing to do? Or should I just dig them up and replant?

    • says

      You did fine Lauren. Keep in mind zucchini and squash will commonly show signs of mildew on the leaves. Once it’s there, you can’t reverse it–just try to keep it from spreading. Removing the culprit is typically a good choice. But with zucchini and squash, most leaves will show this so removing them all will leave your plants looking pretty bare. As long as you have new growth coming on, you should be fine. Just try to stay on top of the problem. I like the milk and water option. Good luck.

  7. Paul Marshall says

    have had a terrible problem with pm in my community garden in Salem Oregon with any squash.Would Korean squash be the answer… ? How do I get starts or seeds?

  8. candy says

    Hi Joe,
    Just read this article and glad I did.
    I’m new to gardening and this morning I found PM on most of my potted plants and flowers. I treated all the plants and cut away the really bad foliage. While I was washing the dishes I noticed the palm trees in the back yard have what appears to be PM and some black spots. Could my plants have gotten it from the trees? My tomato and basil sit under one tree. How do I treat the trees? Do I treat everything back there?
    Thank you,

    • says

      Candy, you don’t need to worry about treating everything. Only certain plants are susceptible. And black spots are unrelated. I would treat what you know to be PM where you can and let nature take its course with the rest. While PM is unsightly and does influence the natural growth cycle, it’s rarely so serious that you need to worry beyond what you can reasonably do to treat it.

  9. Pam says

    Hi Joe,
    Can powdery mildew be treated with neem oil?? Someone told me to use this but from what I read it Is for pest not fungus.

    • says

      Pam, while neem oil is great, it’s not used as a fungus control to my knowledge. While it can help with certain diseases such as black spot on roses and as a deterrent to some pests, mildew is not one of them.

      • Tony says

        Joe, you recommend Neem Oil. I went back and checked, and sure enough you do. What do I make of this?

        • says

          Hey Tony. Thanks for calling me on this. I am going back to clarify my position on Neem Oil as a control against powdery mildew. While it does give some control, it just doesn’t compare to the results of baking soda recipes and even milk and water. I always opt for organic or natural solutions if possible. Neem is a great product for some things but when it comes to controlling PM, it’s just OK but not high on my list.

  10. Robin Cooley says

    Thank you for all those great suggestions. My question is, if I had an outbreak in my garden last year, do I need to treat the soil, prior to planting this year. I lost a lot of plants last year.

    Thank you

    • says

      You don’t need to treat the soil Robin. The best treatment for powdery mildew is stay proactive and start treating the foliage at the first signs of problems (or even before it happens is best). Once you have it, all you can do is try to prevent it from spreading. So the earlier you catch it, the better chance you have of keeping it in check.

  11. Julia Brode says

    Have you tried Korean squash? I figured that since it was humid there, it would grow here. It also gets the powdery mildew but continues to produce wonderful crops. It is a type of ball squash and is sweeter than zucchini which I have given up on due to the powdery mildew. I did have some success with some zucchini seeds from a website that is resistant to powdery mildew but it costs so much to mail I decided to get the Korean squash instead. Make sure you trellis it as it likes to climb. You won’t be disappointed. My Korean friend brings it to me from Koreatown, Los Angeles.

  12. Bunty says

    any ideas about the ratio of water to milk when using Evaporates milk? This milk is concentrated .

  13. Dionne says

    Hi, I’m a complete newbie, trying my hand at growing spaghetti squash, and am now battling with the PM. Do you apply the neem oil directly to all the affected leaves or just on the new ones to stop them from getting the PM? Also, do you need to mix the neem oil with anything, or just use as is?

    • says

      Hi Dionne. Mix the neem oil with water as directed and spray to the entire leaf surface. You won’t hurt anything this way but it should help as a deterrent to preventing its spread. Neem is one of the best organic controls I know of for controlling disease and acting as a repellent to some insect pests.

      • Dionne says

        Thanks for the info, so far I’ve been trying the milk method and it seems to be slowing down the inevitable. I was looking through the entire thread, but I don’t see anywhere about the ratio of neem oil to water, so I’ve been hesitant to try it. Could you give me an idea?

  14. Robert says

    Lots of good information, but I grow peas to eat and then turn the leaves and stems into the soil. If the peas get PW should I discard them rather than take the chance of infecting the soil? Can the spores live in the soil and infect the next crop?

  15. Dane says

    I think the milk and baking soda up the ph of the water and powdery mildew likes a more acidic surface.I found using ph up to up the ph of your water to 9.5 and spraying plants works well without leaving any white spots like milk or baking soda.Do not water plants with ph that high just spray the plant.

  16. Nancy Varner says

    Would like to know what plants you can plant (next year) in the area where P.M. was on my squash plants this year?

    • says

      Hi Nancy. Powdery Mildew is most common on certain plants, while others rarely or never get it, even when planted in the same location where your squash for example was ravaged by it the previous year. So by avoiding the most susceptible edible plants of powdery mildew, you will likely dodge the problem all together, even if planting in the same location the following season. In my garden, the plants most often affected are squash, cucumbers, and cool-season peas.

  17. Eva K says

    Wow! Lots of great ideas on handling PM. I purchased a home with an amazing garden 3 years ago. I haven’t made too many changes, last year I started thinning some of the plants. I noticed PM on my peonies, but didn’t think much about it. This year has been a HUGE struggle. Between PM, black spot, and some insane insect activity I have spent more time trying to save my plants than anything else. I have come to terms with the loss of most of my new additions and the fact that i got only a few blooms from each plant this season. My question is what can I do to help save next year’s garden? Massive cut backs seem to have helped my roses, but the PM persists. I would prefer natural or organic methods, but will resort to chemicals if it means saving the plants. I have such a large area that spraying every plant on a regular basis seems unrealistic. Its also the end of the season. I plant to cut down as much as possible and remove every last bit of mulch. But what next? Is their a systemic treatment i can douse the soil with? should i use compost to protect the flower beds instead of mulch? is there any point in spraying this late in the game when everything is dying or will be cut back? What should I do in the spring? This property lured me in with the beautiful garden, but I am definitely in over my head and need all the help I can get.

    • says

      Hi Eve. My best advise is to stay ahead of the problem. Here in Atlanta where it’s hot and humid, blackspot and powdery mildew is a huge problem. One of the very best rose growers I know is religious about spraying her plants with Neem Oil mixed with water. She coats her plants with it every week or two. It keeps her roses looking beautiful and disease free, and all organically.
      To target the powdery mildew specifically, I would stay ahead of the problem by using the 2 parts water to one part milk spray solution.
      Again, the key is being proactive with this and treating your plants before symptoms become visible.

    • Suzanne Hodgkins says

      Hi! I read that you can eat the fruit of plants that have PM, but can you wash off the kale and eat that? …i washed it, tossed it in olive oil and baked it into chips… it didn’t SEEM to bother me!

  18. Andrea says

    Hi Joe,
    Back in August you wrote, “The fats in the milk are what makes the difference”. With that in mind, will whole milk work better than 2%, 1% or skim, fat free milk? I pulled up my entire raised bed this morning, which contained a lot of moldy zucchini leaves, and I found this site while looking for a way to treat the soil now in preparation for next spring. However, from what I’m reading, it doesn’t make any difference if you treat the soil for powdery mildew. Nothing winters over. Am I correct? Is there a treatment? (I think it’s a psychological thing…I feel like the soil must harbor some residual nastiness)…
    Thanks for this site. It’s a very helpful resource for novices like me!

    • says

      Hi Andrea. I checked on your question with Dr. Jeff Gillman who conducted the study. Here is his reply:
      “it’s actually the lactoferrin that seems to be the active ingredient against disease. It is possible that the fats help this compound to stay on the leaf. When I ran trials we used whole milk, but researchers have found success using a number of other types of milk including skim and powdered.”

      Hope that helps. And glad you find our site is helping you overall too.

  19. Carl says

    Thanks for this insight on powdery mildew. It appears that it will not be a problem to compost my mildewed plants.

    However, in the article you state,

    “One experiment showed good results by applying a weekly dose of one part milk to two parts water. This is yet another case when more is not better. Concentrations above three parts water had adverse side effects.”

    I am confused as to what you mean by “Concentrations above three parts water … “. Three parts water to how many parts milk?

    I guess I’ll try the one part milk to two parts water formula next spring to combat the recurring powdery mildew problem I experience.

    Again, thanks for your efforts.


    • says

      Hi Carl. Thanks for catching that comment and I apologize for the confusion. That line was part of an edit that should have been deleted. Stick with the one part milk to two parts water and you will be fine. I’ve deleted that part of confusion. Thanks again.

  20. says

    A portion of my lawn has what I think is powdery mildew. It is in the shade and only some of the blades of grass have a while tinge to them.. How would I treat this? Milk?

    • says

      There’s no way to know exactly what the problem might be without seeing it Louise. A great resource for this or other plant-related problems is your local county extension office. You can take a sample by (be sure to include healthy and diseased parts) and they can analyze the issue and diagnose the problem to suggest the best solution.

  21. cyndi c says

    Is powdery mildew spread if shears or scissors aren’t washed after using on an infected plant?

    • says

      Hi Cyndi. The following reply is directly from Dr. Jeff Gillman to your question:
      “In terms of powdery mildew — sure, dirty pruners could spread it from one plant to another, but powdery mildew is really a disease of the leaves not the stem, so it’s not something I’m particularly concerned about — I’m much more concerned with uncleaned pruners spreading canker diseases or fireblight”.

  22. Angela says

    I have been fighting powdery mildew this season. I got it in my vegetable and herb garden. I sprayed my squash and cucumbers with the baking soda, dish soap and water solution. And for my dillweed, I just cut it out and got rid of it. I had a few volunteer dill plants come up. Well, they are getting infected! It has been about a month since I cut out the infected dill. And our weather has been mild with normal rain. Why am I getting the mildew back on the new dill? Is there anyway to treat the bed to kill all the spores?

    • says

      Jen, I’ve not tried this nor recall seeing anyone using this to fight powdery mildew. D.E is used primarily as a pest control, since the fine particles are sharp and desiccate the tissue of soft bodied pests such as snails and slugs. I don’t think D.E has any properties that would fight powdery mildew.

  23. John M says

    Joe, you have a great site. I read all your info about milk and PM. I have a well established infection of PM on a number of my Hibiscus in my greenhouse. What is your suggestion?
    The PM is on the trunk and stems. Thanks, John
    PS I hard cut back hard each fall so there are few leaves to contend with.

    • says

      Hi John. I wish I could give you more concrete help here. Once you have PM on plants, it’s hard to cure or reverse it. But the milk / water solution should keep it in check. I would continue to spray exposed areas with this periodically and see if we can keep it from spreading. Time will tell. Good luck and if you get a chance, please shoot us an update on this page so we can all learn together.

  24. Aimee Kaczorowski says

    I found powdery mold on my house plants leaves but not in the soil. How do I go about getting rid of that? It 1st started on 1 of my plants an I took it outside an cleaned it an changed the soil well now 2 others have it as well. I’ve read several sites but they all talk about the soil. What can I do?

  25. Nancy says

    Back to the milk. I have not been so impressed with 1 part milk to 9 parts water which is what I have read everywhere else. Where are the studies about the 1:2 solution? So far my best player has been simple cold pressed NEEM oil but it has been a battle all summer. I may give it a go….I only get a few days on the NEEM

    • rob says

      what i do is 1. spray with cinnamon cca teaspoon for a liter..first boil the water after add the cinnamon..2. spray cca 3 days after with milk-2 part milk-1 part water 3. spray again cca 3 days after with milk..always work

      • Joanna says

        Rob, 2 parts milk to one part water, or two parts water to one part milk? Also, what does cca mean?

        Thanks in advance!

  26. Amy says

    Thanks for all the information. I was so disappointed to see this happen again this year. After last year, which was the first time I experienced this, I raised my beds higher and replaced all the soil. Not a very cheap thing to do, money-wise or time-wise, but I thought that would clear the problem. But it didn’t. We’ve had a string of very humid weather days here – which is when it all started. I’ve noticed that the veggies now are either dying before they mature or are weird shaped. Is that all because of the mildew? Looks like it’s going to be the end of my season :-( Glad to know it’s safe to eat what is there at least!

    • says

      Amy, misshapen vegetables are usually the result of poor pollination. The mildew could have an impact on their inability to not mature as a result of unproductive leaves covered in mildew. But my suspicion is def. lack of pollination first and foremost. You can hand pollinate next summer if you want to make sure you have more fruit that makes it to maturity and properly shaped. Good luck.

  27. Ami says

    Hello. Thank you for this website! I knew that my squash plant had leaves that were turning cloudy white, but today I found several leaves that were covered in the power white thing. I’m going to try the water/milk mixture tomorrow. My garden is such that I can only water from above, making the whole plants wet. Should I reapply the mixture every time I water?

    • says

      Hi Ami. Yes, if the foliage gets wet, re-apply. I know that’s a hassle but it’s necessary. By the way, just want to make sure you know this milk solution works best as a preventative, not as a cure to reverse an existing problem. So it works best if you start applying before you see any signs of problems. But since squash leaves are so susceptible to mildew, you can safely assume you’ll have this problem next season if you had it this year. Begin spraying before any signs of trouble show, and after any rain or overhead watering.

      • Ami says

        Thank you for your reply, Joe. I tried this mixture, and pooph! My plants are saved :)

        Other than the several young leaves, most all leaves were infected. I cut the leaves that were heavily covered in mildew since I figured they would die no matter what I did. But many of the leaves that were almost completely covered in mildew are now bright healthy green after only two days (I sprayed each day). There are some leaves that are turning yellow on the edges, and those would probably still die. But I’m amazed that milk/water worked so well! I understand that this is best used as a preventative measure – I will spray on a regular basis this year, and before the mildew appears next year. Thank you so much!!!

    • Arrana says

      Hello! I can’t seem to find the reply button to start my own question, so my apologies for piggy backing on someone else’s. I live in Connecticut & not only is the mildew a problem but the squash vine borers are horrendous, I am currently trying my hardest to evade them. I am not changing the subject though, because what happens is after the SVB’s attack a plant (currently zuccini) the powdery mildew takes advantage of it’s week state. I went away for 2 weeks and came back to SVB damage and spreading mildew. I apply milk during the day and neem at night & although the plants are still slowly producing I’m in a constant war, as the mildew spreads to the cucumbers and even tomatoes!!! Lots of background just to ask this one question, should I cut off the worst leaves??? Leaving more air circulation for the healthy ones or will this also compromise my poor plants health?? Thank you for your article and in advance for any reply:)

      • says

        Hi Arrana. The quick answer is yes, you can and should cut off leaves that become too infected with mildew. they become very unproductive. Squash is very susceptible to PM and hard to control. The squash vine borer needs to be treated at the earliest stages.
        Try applying B.t (Dipel) at the base of the plants to kill the larvae before they affect the plants. If you find that they have gotten into the stems, you can try to extract them by slicing into the stem near the entry hole to remove them. Then mound soil over the same area and the plant should recover. But the PM has to be treated separately.

  28. Sheena says

    Looks like I have some mildew in a few spots, due to garden veggies growing like magic from our llama doo. We are an organic habitat, ponds, tons of wildlife, domestics, exotics, sweet fish, turtles,fowl and more! Will milk or vinegar etc., harm the many Lil frogs working happily in the veggie paradise? I can’t harm these blessed creatures! Thank you for a great site+show also!:). CA

  29. Mary says

    I have 8 ornamental grasses – Miscanthus Gold Bar (Maidengrass) that appear to have powdery mildew. The white powdery substance is all along the leaf sheaths, and in between. Every time I peel back a leaf, I see the mildew. I used a ready-to-use sulpher spray, but have not noticed any difference in the fungus. Would your milk recipe help on ornamental grass? Thanks

      • Joanna says

        Joe, that’s nice to know. And is it also safe to ingest herbs that have powdery mildew on them? I just cut my rosemary bush WAAAAYYYY back and sprayed milk (1 part milk to 2 parts water) all over the plant, and a lot got onto the soil as well. I hope I did the right thing!

        TIA for your reply.

        • says

          Joanna, I don’t know of anyone that has died or even gotten sick from eating plants infected with powdery mildew. Having said that, I don’t advise it. But for me, I would either not eat those leaves or wash them off thoroughly. Then you should be fine. But, going back to your other question, I don’t think you have powdery mildew on your rosemary. I still think it’s wooly aphids.

          • Joanna says

            Thanks Joe, I so appreciate your reply. Whatever it was, it’s completely gone! I confess, me being me, after cutting all affected parts off, I sprayed the milk on my rosemary plant three times on the first day. I applied again after one week, and will apply again after another week. My plant is completely free of whatever it was and it’s growing so beautifully now! I’m in love with it all over again!

            But I have another question for you. In another place, I have an indoor planter that I just filled with organic soil and have transplanted seedlings and planted seeds. This morning, I noticed that some of the seeds have sprouted (and the transplants are doing well) but there’s also a white sprinkling stuff on the surface of the soil. It looks like a tiny bit of frost, but obviously, it’s not. What in the world could this be, and how can I get rid of it? I’d be happy to send you a picture if possible…

            TIA for any advice you might be able to send,


  30. Jeri says

    I tore out some petunias that were badly infected with powder mildew. I would like to replant, but do I need to treat the soil first?

  31. amanda says

    Will milk alternatives work? Soymilk or almond milk? I know most people say these aren’t even milk, but I think I remember reading some where that the milk spray works because of the protein. If this is true, then these alternatives should work as well? Has anyone tried this?
    I have a great garden going with my children! They would be heart broken if our cucumbers didn’t finish growing!!

    • says

      Hi Amanda. Unfortunately soy and almond milk will not work – they have protein, but not the protein lactoferrin which is what stops the disease.

  32. Becky says

    I don’t usually go back and reply on websites, but I must say I was very impressed with using the milk method on powdery mildew. I have a new climbing rosebush and just as it was growing well, the powdery mildew came. I first cut it off, then realized it was spreading other places. I read this info on your site and did the milk and water application. The first week I was amazed that it was disappearing. A week later I have now applied it again. I’m so thankful!

  33. Cathy Outlaw says

    I just posted a comment yesterday. I did further research and realized that my plants had a mealybug infestation, not powdery mildew. There are thick white globs up and down some of my pots, which now I know is an indication of mealybugs. So, my concoctions of milk and water were useless! Instead, I’ll get out the alcohol and wipe off all my pots. Quite disgusting!

  34. Mac says

    Sorry! It’s Mac again. Forgot to say where I live! We live in POETRY, Texas. Northeast of Dallas. We are in a drought that is in it’s 3rd year. 9 years was the forecast! Using water containments and water barrels at every gutter down spout around our property. Growing food or ANYTHING is so difficult. Our water has a form of chloride that can not be dispersed. My husband, bless his heart, is exhausted! Wet weather is expected for fall! Hope so!

  35. Mac says

    You are a TREASURE found just in time! Would non-fat dry milk (mixed as directed) be ok? Tried to save my mildew covered honeysuckle using potassium bicarbonate, natural soap, and vegetable soap with a little success. Started making and using AWSOME !steeped compost tea on everything regularly! Each day I picked diseased leaves off as new ones grew in. Now that you have shared your knowledge about milk for powdery mildew, it will be faithfully sprayed as a preventative once a week. Should it be applied even in the fall and winter? Thanks so much for sharing such GREAT information!

    • says

      Thanks Mac. You can use non-fat milk. The active ingredient is still present. As for spraying over fall and winter, the leaves susceptible to this for all that I can think of are deciduous so you won’t need to spray then. The leaves will be gone by then anyway. Just keep ahead of it starting next spring.

      • Joanna says

        Oh oh, so does that mean that the white powdery stuff I have on my rosemary isn’t powdery mildew? I should mention that I live in north-central Massachusetts–snow outside, but rosemary plant inside, under grow lights and otherwise doing very well!

        TIA for replies.

        • says

          It’s not Joanna. Rosemary is not a host to powdery mildew. I think it’s either residue from insect pests and perhaps specifically wooly aphids. Google that and see if you agree.

  36. Cathy Outlaw says

    I’ve pulled up the plants in the one area in my yard that was infected with powdery mildew. It’s in the shade, the plants were crowded, and they were dying so they looked really bad. With no remaining plants in that area, what can I spray to kill the spores in the dirt and mulch? I plan to replant that area eventually, but want to take steps to prevent reinfection.

    • says

      Cathy, I wouldn’t spend time trying to do anything with the soil to prevent future cases of powdery mildew. If conditions are right for infection and you have susceptible plants, airborne pathogens will infect your plants regardless of what you do in the soil. Look for resistant varieties and monitor your watering methods and provide good air circulation whenever possible.

  37. Katherine Lang says

    Wondering if I can use milk that has gone bad? It’s not curdled it’s just sour, past expiration date milk. Do you think it will still work??
    Thank you!

    • says

      It will work Katherine. It’s a logical question but since the plants are drinking it, they won’t care. It’s whats in the milk that matters. Thanks for your question.

  38. tom says

    We use various strengths of bleach solutions on all sorts of fungal problems. Why can’t we use a mild bleach spray on say cucumbers or squash and then rinse it off in 15 or 20 minutes?

    • says

      Hey Tom. I spoke to Dr. Jeff Gillman about this. Here is his reply: “First, that is very dangerous to your plants. Some can handle it, but many can’t. Second, bleach will sterilize, but then it disappears. A big part of the reason that milk works is that it remains on the plant to protect it.”

      Good question and glad you asked.

  39. Susan says

    I have two columnar oaks already quite high. They have brownish bumps on the bottom of leaves and fungus on the top. This was the case last year as well. A professional did deep root feeding. The leaves came back this spring looking very healthy but now in July we have the same problem. I could use the milk idea but it would be a big job. I am wondering if one does nothing will the tree always look great in the spring and then in July develop this disease but not really kill the trees.

    • says

      Hi Susan. You likely have a leaf gall which is very common to oak trees. It’s cosmetic only and will not harm your tree. I get them all the time and do nothing. My trees are fine and continue to thrive year after year. If you want to confirm this condition, take a sample to your county extension service for verification.

  40. Karen says

    I applied milk water solution to my squash and cucumber that both have powdery mildew yesterday and they already look better, how often should I do this? I saw mention every 2 weeks but was that just for prevention or also for present mildew problem? Thanks for article!

  41. Cyndy White says

    If I use milk I eliminate powdery mildew on be squash, does that affect people with milk allergies? This is for a school garden.

    Would you feel that baking powder with ivory liquid soap and water would be best on powdery mildew? What about a bad case of powdery mildew, where the leaves are already yellow?

    Morning, afternoon or evening treatment?

    Thank you.

    • says

      Cyndy. I don’t know about how this would impact people with milk allergies. I think a doctor specializing in this would be the best source to find out but it’s a very good question. If you find out, please report back and let us know.
      I have my doubts about baking powder with ivory soap and water. The fats in the milk are what makes the difference and the baking powder doesn’t have it. Although the formulation you mention is a good natural disease control, I’d stick with the milk solution if possible.
      And as for plants already affected, you can’t cure powdery mildew. Only halt its spread. Once it’s there, it’s there. So best to start spraying before there is a problem. Spraying after the fact will only slow or prevent its spread.
      For application time, I would spray in early morning, before evaporation kicks in but so that foliage doesn’t remain wet too long, as if you sprayed in the evening.

  42. Jennifer says

    This morning I sprayed a 50/50 solution (milk/water) on my squash, pumpkin and cucumber leaves… and then I just came across your site and read, “Concentrations above three parts water had adverse side effects.” What are the side effects?

  43. Ariel says

    I am a first-time gardener this year in Florida, and soon found my glorified dreams of a successful apartment balcony container garden under seige by that nasty powdery mildew crap I had only read about in passing and while skipping over lots of reading since I assumed nothing could threaten my screened-in plants. I was so frustrated I gave up on some of my plants, worried food from these plants wouldn’t be edible because the leaves become quite disgusting. Can food be harvested from a withering moldy plant? Bleh

    Anyway, this webpage is a lifesaver. Thanks for giving me several eco-friendly options to combat the horrifying powdery mildew and giving me renewed resolve in learning to garden!!

    • says

      Thank you Ariel! So glad you found our information helpful and that you took the time to write us about it. Never give up. Just try and learn from your experience. That will make you an awesome gardener!

  44. Susan Gelderbloom says

    Would Diatomaceous Earth also work? Since I have a two fold problem in my garden (broccoli and cabbage being eaten to bits) I was hoping to be able to use a single product. I just puffed my veggies with the DE but it only works if dry.


    • says

      Nice idea Susan but I’m pretty sure that won’t work. DE is used to cut into the tissue of soft bodied pests like slugs. It has sharp edges so when a slug or snail passes over a dusting of DE, it can cut them and they dry out and die. But theres nothing about DE that will kill Powdery Mildew.

  45. Jami says

    HI Joe… My name is Jami and I am kinda new at this whole plant thing. My front porch was looking a little bare so my Mom and I did a little day project about 4 months ago and I have fallen in love with plants and can not stop myself from planting more. but in the last month I have notice this powder mold you are talking about. I am going to try the mouth wash thing tomorrow during the day. But I was wondering if I covered my plants at night? if it would help with the problem. I live in Monterey,Ca and I am a stones throw away from the beach so I am wondering if the night foggy air would be blocked from a thin sheet over the flowers? Please help because I am so disappointed when I look at them because I feel like they are suffocating!

    • says

      Hi Jami. I totally get your newfound addiction to plants. Good for you. As for your idea of covering your plants at night, I’d advise against that. One of the most important things your plants need to keep diseases such as mildew from getting worse is air circulation. By covering your plants at night, you’re actually trapping moisture and preventing air from helping your plants.
      I would suggest you try spraying the leaves with a solution of 2 parts water to 1 part milk. Do it every week and get all the leaf surface, on top and underneath. Also, keep in mind, some varieties of plants are far more susceptible to powdery mildew than others. But treating them the way I propose will do far more to kill the spores than covering your plants at night. Good luck.

  46. Cookie says

    I’m gardening this summer in a “community garden”.
    My garden neighbor has a huge powdery mildew problem. The neighbor is not treating his garden.

    My squash, zucchini , and cucumbers have been severely damaged by the powdery mildew.

    What I’ve done about the problem:
    First I trellised my plants.
    Then I pulled off all the badly infected leaves.
    I’ve removed 2plants that were beyond help, determining it was better to concentrate on the healthier plants and remove as much of the fungus from my space as possible.

    I started with the neem oil – it definitely works. I’ve applied all my solutions in the heat of the afternoon. I have quite a few herbs near my infected plants and felt uncomfortable that the neem oil mist was drifting over to my mints and lemon verbena . So I switched to organic apple cider vinegar – I did not think the vinegar was affective . But I could have tried different concentrations but decided to Switch to milk..
    I’ve applied 3 sprayings of buttermilk, 1 part milk to 2 parts water. My plants love it! I think the leaves actually grow faster and the leaves are greener looking.
    –my theory — I’m actually consistently spraying and I’m actually pretreating the new leaves and pulling the infected and I’m producing a new healthier plant — just my theory.

    During the past 5 weeks I’ve removed all the badly infected leaves on my plants. At one point, one of my cucumber plants probably had 2/3 of the leaves removed.
    I’ve been desparate to keep the fungus under control. Most of the gardeners in the community garden have been infected with this powdery mildew and it’s my opinion the gardeners who leave their plants on the ground seem to have the quickest infestation and the gardeners who trellis are better able to control the powdery mildew.
    I find it easier to spray the plants on the trellis – I can get to all sides of the plant and walk around and spray more effectively.
    If I grow squash, cukes, and zucchini. Next year I will definitely trellis, prune, and spray early to prevent the fungus.
    I also wanted to mention that it’s my opinion the gardeners who water in the evening have the worst fungus problems. I water in the early morning – with a strong dispersed spray – I DON’T “gently shower” my infected plants. I’ve been giving them a good heathy strong spray in the mornings.

    My plants have been spending a lot of energy growing more leaves and I’m not getting the yield I should but the plants are healthier now and have been producing.
    Hope this helps other gardeners.

  47. Roberta says

    Your info on powderly mildew was most helpful!! I live in the rainy state of Washington and have been noticing this on my petunias and pansies primarily. I appreciate the help!

  48. Anne Garcia says

    Hello to you, Joe Lamp’l. Your site was the first to pop up when I typed in powdery mildew and the one I clicked on. I live in Illinois about an hr. NW of Chicago. I would like to thank you for your excellent information on this subject. The plant attacked with this mildew is the beautiful Bee Balm. I’m going to try the mouthwash since it has spread all over the plants. I’m hoping to eradicate it. I will let you know. Also what I found quite nice was that you take time to reply to everyone. I also was confused about the Neem Oil and the Dormant Oil. Thank you for explaining what they are. We have had nothing but hot humid weather here. Do you offer a site that shows pics of the most common ailments of plants? Thanks for the great info. Very glad I found your site.

    • says

      Hi Anne and thanks for the kind words. I don’t have a sight that has what you’re asking for, but it’s a great idea. Glad you found our site too. All the best.

  49. mary says

    my apple tree has white powdery leaves can i wash them with the soap and baking soda its not planted yet

    • says

      It shouldn’t hurt Mary if you don’t use too much soap. Soap can dry out leaves to excess and result in burning. The baking soda is good though. But try the spray solution of two parts water to one part milk. That’s safe and effective. Spray about once a week or more often if rain washes it off. Once you have mildew, it’s hard to reverse what’s there, but you can reduce the spread with spray.

  50. Valerie Torres says

    Hi there! I am new to the whole Powdery Mildew thing and just sprayed a 1:5 milk solution to my baby squash. Flowers were falling off prematurely and initially, I just cut off all of the affected leaves. Seemed to work, because now I see squash and the flowers are staying on! But, the powdery mildew came back with a vengeance! So, I sprayed tonight, but it was around 6:30pm. Now I am reading it should have been during the day? And the plants are not in Full Sun. Should i move them to get at least 6 hours of sunlight? I live in Italy, near Venice, and it is super humid here!! 80% humidity! Yikes! Help please… 😉

    • says

      Don’t move them now Valerie unless they’re in containers. I think your humidity is the biggest culprit and there’s nothing you can do about that. The mildew on squash is almost a given. I too struggle with it in my Atlanta garden. It’s more of a race to see how much harvest I can get before the plants finally succumb to the mildew. The key is air circulation. So if in containers, give them full sun and lots of air circulation. Or, next time you plant. Good luck.

  51. Traci W. says

    HI Joe! Love your site. I have recurrent powdery mildew on my tall phlox. I have spaced my plants to provide plenty of air circulation and the milk remedy with no success. I am going to try the Neem oil or one of the other treatments you suggested . Should I also treat the soil?

    • says

      Hi Traci. Thanks for your kind words.
      No need to treat the soil. You must make contact with the mildew on the leaves to kill it.

  52. Joan Keller says

    Thank you for the suggestion to use Neem Oil on powdery mildew. We use Neem Oil on minor cuts, bites, poison ivy etc. It is great. I will be applying a weak spray today to my petunias. I will get back to you in a week or so.

    • Joan Keller says

      It has been 2 weeks. Instead of Neem Oil, I sprinkled my petunias with a weak baking soda solution; one level teaspoon household baking soda to one gallon of water. After the second application, seven days apart, the powdery mildew seems to be under control. After each application the petunia leaves curled a bit, but, did not wilt. The flowers appear strong and cascading and the fragrance is lovely. I still water and deadhead the petunias daily. They hang with ferns just outside our front door. Thank you very much for the info about baking soda. If the mildew returns I will leave another comment.

  53. Marlene says

    I used the baking soda solution, and also the vinegar solution on my Tuscan Blue Rosemary greenhouse grown. In addition, I used a general fungicide called 3336 which is a milky-like solution with water. Anyway, I placed all the flats outside and are growing beautifully. There remains a white residue on the leaves. I cannot sell these plants with the white residue…or is it mildew (would they continue to grow if the mildew was still present)? Can these plants still be used or do I have to discard them all. Is there a way to remove the white powdery-like residue?

    • says

      I would pick a leaf or two that is covered in this white residue. Examine it under a strong magnifying glass. If the residue is smooth and possibly shiny, it’s the coating from the fungicide spray. It does that. If it’s this, it will go away eventually. If it’s mildew, you should be able to see that it is not just a coating on the surface but also has depth. If it’s mildew, the treatments will help stop new mildew but won’t erase what’s there already.

  54. Kirsten says

    I have a mini rose plant that is only kept indoors. I noticed the mildew just today and I want to try the milk treatment. Does the type of milk matter? I have skim milk, but I didn’t know if that was as effective.

  55. says

    Hello there. I sprayed at the 1:10 mix having quickly read your article before the correction. I am spraying lettuce, so any taste or residue is important. I’d like to know how long the reaction takes. Is the milk’s effectiveness stopped at drying or should it sit for a day or two?
    I plan to rinse with water instead of the normal irrigation cycle. I will post any interesting findins and also use the 1:2 ratio for a test plot.

    • says

      In university trials, the spray was effective for about a week with good results. Dr. Jeff Gillman who appeared on our episode where we addressed this says he thinks you can go 2 weeks between spraying.

  56. Gul Hassan says

    Hi JOE LAMP i am Gul Hassan from Afghanistan i am Studies you are all topic about the powdery mildew it use full for me but I am not understand on neem tree oil and dormant oil, if you have time kindly explain it with image or other synonyms which we will find it in market.

    • says

      Hi Gul. Neem oil should be sold as just that. It should say “Neem Oil” on the bottle. Dormant oil on the other hand, it a highly refined grade of horticultural oil that may be sold as “Horticultural Oil”. It is used to spray on trees and shrubs during their dormant period to suffocate overwintering pests. Need oil is used during active growth to help control plant diseases and to repel certain pests. They are used for completely different reasons so one would not be a substitute for the other. Hope this helps.

  57. says

    I’m a bit confused about the “milk” solution to fungus. It suggests 1 part milk to 9 parts water as being effective…however, it goes on to say that anything above 3 parts water can have adverse side effects! So, where is the recommendation? Did I misunderstand something?

    • says

      Hi Charles and thanks for catching this. No wonder you were confused. The “1 part milk to 9 parts water” was an error. The correct ratio is 1 part milk to 2 parts water. That should also clear up the confusion. It has been corrected in the post. Thanks again.

      • mark kimball says

        You say to “apply the milk and water solution weekly” what does apply mean? as watering or as a spray?


        • says

          spray it on Mark. Get a cheap spray bottle at the hardware store, mark it with a sharpie and coat the leaves on both sides each week. Watering on the other hand will do no good. You have to coat the leaves.

      • Mark Plourd says

        I found 1part milk to 2 parts water was a bit to much milk , just a little less than 1/3 worked great to get rid and control the white powdery mildew as well as the plants seemed to respond with health due to using it . I have to spray once in a while but not often and I have alot of rain with low light .
        The black fungus that was talked about that kills trees , schrubs , plants over night I sent in to have it analized . I was told it comes naturally from tree’s . I was told the studs in walls of the house you attach drywall to has it in it naturally . How to kill it , great question , it still is happining and I’ve never seen anyone come up with a way to beat it without killing the host plant as well . If the answer was found it would help alot of people where I live . It kiils inside grow rooms as well as outside plants , it’s not picky but loves weak plants . That’s all I can say about it other than it looks like the leaves have been burnt with black fire and can kill a 6 foot plat that is healthy in 2 days . I watched and could do nothing about it , I tried though , zero sucess . I had to fight back but that’s all I could do . Organic soil grows is what I was doing indoors . I found the smae black fungus this year outside Organic soil growing , so it’s everywhere .

  58. Pam Bradberry says

    This was helpful. I’m going to try the baking soda remedy first.
    1 Tablespoon baking soda to 1 gallon of water

  59. Kim Winstead says

    Hi, i live in North Alabama & I have a terrible case of the black & white mold, it’s on my trees & it has spread to every flower, shrub etc.. That I have. It killed my Lilly tree. I really need help ASAP. I have cut back the branches in the trees that it was on & raked all the leaves in the area, but my elephant ear & other flowers haven’t started coming up & I’m afraid they have been killed due to this mildew problem. I really need your help.

    • says

      Hi Kim. I can’t say with certainty on how to deal with this widespread outbreak and have never experienced this problem so I cannot offer any firsthand solutions. But if I were you, I would contact your county extension office and speak with the agent there. They are far more up to speed on local problems and solutions backed by university data and research. If anyone can help you, I would start there. You may need to take samples of infected and semi-infected plants so they can conduct a thorough analysis. Make sure you discuss this when you call. Good luck.

  60. bernadette says

    Hi, this summer 2013, I had the worst case of mildew. It spread to shrubs, and flowers (clematis), all round the garden. It may have come from plants I overwintered in the shed, (unsuccessfully), or for the shrubs I think I was too zealous over watering every day. I cut it down to once a week and never watered the privits as they started to rust.
    My question is, I was thinking of using potassium bicarb, or plain bicarb (I use this on the fish). Do I wait for the leaves to grow or can I spray whilst plant is dormant?
    Also, my experience with shop bought fungus treatments is its lethal to wildlife. I lost a fish spraying a magnolia, even though pond was covered apart from furthest 6 inches. Later, bees started to die in the garden. I left the plum tree to ‘survive’ as my rabbits lived underneath. Is potassium safe for wildlife?

    • says

      You need to spray it while the plant is actively growing to coat the target “host” area of the disease but you need to do this before you encounter an outbreak. Prevention is key. Once you have the problem, it’s more about keeping it in control and from spreading.
      Your point about the consequences of using this to wildlife and aquatic creatures is important! People fail to consider this all too often. I’d rather have a bit of cosmetic damage and protect the creatures. Thanks for making that point.

      • T.A. says

        I’ve got the mildew. Live in east Ala. and it’s Dec. What can I do to get through the winter and fight the mildew this spring or do I need to fight now. Help!!

        • teeb says

          Milk saved my entire spagetti squash crop last year! I was spending $25 a week on fungicide that barely was effective. I read about using milk and tried it with huge success! MILK!!! MILK!!! MILK!!! WORKS!!!

      • Mona says

        So you’re saying that my peonies bushes that have this (moved in last year and noticed it and back this year) will always have this every year? there is no way to get rid of it completely other than digging out the bushes and tossing them?

        • says

          Don’t think I said that Mona. Although some plants are highly susceptible to powdery mildew, some moderately so, and others resistant, the ultimate determination will be the environmental conditions required for mildew and other diseases to form. For any disease to form, three things are required. It’s called the disease triangle; 1: An appropriate host, 2: specific environmental conditions, 3: The presence of the disease agent, i.e spore(s). All three have to be present at the same time. Otherwise, disease will not occur.

    • says

      Good question. I suppose you could use the neem as a way to help the baking soda stick to the foliage in place of detergent or soap. And you might get the bonus of a pest repellent also. I don’t know of a downside here but don’t hold it against me if something does happen. But I’d love to hear out this plays out if you do end up trying it. Keep us posted please.

  61. Anne Lawless says

    I love growing tuburous begonias so it was good to get info as there seem to be lot of it this year, thank you