How to Prevent and Control Powdery Mildew on Apple Trees

While powdery mildews don’t kill their hosts, they sure do a number on them. And that is particularly true for powdery mildew of apples and crabapples, Podosphaera leucotricha.

The apple powdery mildew attacks both cultivated and wild apples and crabapples. And it occurs in the all regions of the world that produce apples!

Powdery mildews get their name from the white spores that are produced by the mycelia (fungal threads). The disease on apples attacks virtually every stage of the plant – buds, blossoms, new shoots, leaves, and fruit.

The disease can be severe enough that no fruit form.

Close up a limb and leaves of an apple tree covered in powdery mildew.

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While fungicides are the standard treatments, there are some cultural practices that can help control this disease.

Unlike most fungal infections, apple powdery mildew spores do not require moisture to germinate. Therefore, this infection is known as the “dry weather disease.”

Read on as we at Gardener’s Path walk you through the steps you take to diagnose and treat powdery mildew infection on your apple or crabapple tree.

Symptoms of Primary Infections

If your tree is infected, the first thing you will notice is a delay of up to four days in the opening of the infected buds in the spring. These buds are covered with spores.

Next, the leaves and blossoms become covered with the fungal spores as they emerge from their buds. The spores look like a light gray or white powder, and the infected leaves curl upward.

Close up of an apple leaf with a white coating consistent with a Podosphaera leucotricha fungal infection.

Both sides of the leaves and tree shoots will be covered with this powder.

The flowers develop abnormally, are usually greenish-white, and don’t produce fruit.

An Infection That Won’t Stop

These spores are easily blown by the wind and cause secondary infections on new shoots, leaves, and fruit.

As long as the shoots continue growing, the leaves and shoots can continue to become infected.

The infections typically occur at night at 65 to 80 F when the relative humidity is greater than 70%. While this sounds really high, it is common on the lower leaf surface.

An apple tree branch complete coated in a Podosphaera leucotricha fungal infection showing the characteristic white powder-like coating on the leaves.

The disease on the leaves occurs first on the bottoms and may appear like chlorotic spots on the top of the leaves.

As time passes, the tissues that are infected develop the classic silver-gray powdery mildew appearance.

Fruit that is infected will come down with discoloration and netlike reddish brown colors. It may also be distorted and/or dwarfed.

High levels of powdery mildew at the end of the growing season can damage the tree in two ways. First, it can increase the number of infected buds, so you will have a high level of infection next spring. And second, it can inhibit the formation of flower buds, so that there will be fewer or no fruit produced the following season.

Close up of a human hand holding an apple tree leaf shoot infected powdery mildew (Podosphaera leucotricha) fungus.

And if that isn’t bad enough, a tree that is heavily infected with powdery mildew can become susceptible to additional types of infections.

Cultural Controls

You should prune any shoots that appear white in the early spring, so they won’t spread spores.

A pair of human hands uses a pruning tool to remove branches of an apple tree infected with Podosphaera leucotricha.
Pruning and destroying infected areas is one basic method of control. Don’t forget to disinfect your pruning shears between trees and after you are done for the day.

Be sure and disinfect your pruning shears afterwards, and destroy all the infected plant parts, so the disease won’t spread.

Avoid the excessive use of fertilizer, especially in the late summer. This will prevent succulent new tissue from growing, which is easily infected by the fungus.

Another thing you can do to protect your tree is to plant it in a sunny area, since excessive shade, high humidity, and poor circulation all increase the chances of infection.

Fungicides

Since this is such a difficult disease to control, and it is critical to eliminate the spores that will keep infecting your tree, you may choose to apply fungicides. Be sure and choose ones that are labeled specifically for fruit trees.

You have a choice of low toxicity fungicides like horticultural oils. These include jojoba oil, neem oil, and brand name spray oils designed for fruit trees.

Classic fungicides that are used against apple scab, such as sterol inhibitors, are highly effective at controlling powdery mildew. These include myclobutanil and fenbuconazole.
Since the fungus overwinters inside buds, you should start treating your tree early in the season before the blossoms start to show a pinkish color.

The failure to spray before the blooms opens is one of the most common mistakes made in controlling this disease according to the American Phytopathological Society.

Be sure and repeat the sprays at 2-3 week intervals until the new shoots stop growing. That could mean as many as 18 sprays if your cultivar is highly susceptible!

Also be sure to continue spraying even if the weather becomes dry. Unlike most other foliar pathogens, apple powdery mildew continues its growth and spore production in dry weather.

Faithfully applying the fungicides will reduce the need for future applications.

Prevention

You can also spray sulfur fungicides before the symptoms appear.

Be careful with sulfur. You can harm the plant if you apply it within two weeks of a fungicide or if the temperatures are greater than 90 F.

This class of fungicides includes the classic Bordeaux mixture of copper sulfate and lime. This combination is highly effective at preventing powdery mildew and is certified organic. You can buy a pre-packaged mixture designed for small gardens.

Rows of an apple tree orchard with trunks painted with a Bordeaux mixture.
These apple trees have had their trunk coated with Bordeaux mixture, a copper sulfate and calcium oxide in water. This helps to prevent a powdery mildew infection. Though fairly toxic, this method of prevention is considered organic.

The ultimate prevention technique is to plant resistant varieties! Some of the most popular cultivars are the most susceptible – Granny Smith, Jonathan, and Rome for example.

Some of the more common resistant cultivars include:

  • Braeburn
  • Britegold
  • Delicious
  • Enterprise
  • Fuji
  • Gala
  • Jonafree
  • Nittany
  • Winesap

Apple Crop Risk

Although apple powdery mildew will not technically kill your crop, it can debilitate the tree to such an extent that it could be unable to produce any fruit.

This disease is widespread on wild and cultivated apples and crabapples in every part of the world in which they are grown.

Therefore, it is critical to know the symptoms of this mildew, so you can be ready to take action as soon as you see infected tissue.

You will need to spray with some sort of fungicide – sulfur, horticultural oils, or sterol inhibiting fungicides. A strict spray schedule may help save your tree from this aggressive pathogen.

Have you successfully fought off powdery mildew on your apple or crabapple tree? Let us know how your battle went in the comments.

And if you’re still trying to identify a specific disease on your apple tree(s), then some of these guides may be of assistance:

© Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Uncredited photos: Shutterstock.

About Helga George, PhD

One of Helga George’s greatest childhood joys was reading about rare and greenhouse plants that would not grow in Delaware. Now that she lives near Santa Barbara, California, she is delighted that many of these grow right outside! Fascinated by the childhood discovery that plants make chemicals to defend themselves, Helga embarked on further academic study and obtained two degrees, studying plant diseases as a plant pathology major. She holds a BS in agriculture from Cornell University, and an MS from the University of Massachusetts Amherst. Helga then returned to Cornell to obtain a PhD, studying one of the model systems of plant defense. She transitioned to full-time writing in 2009.

41 thoughts on “How to Prevent and Control Powdery Mildew on Apple Trees”

  1. Seems my tree has this, it’s approx 5 year old, I’m unsure of the variety, aldi bought. I’m going to see I can create a natural fungicide to tree with. I’m going to prune the end of September and I will give the first treatment then. In spring when it starts budding, I will start treatment again. Hopefully it works, I will try a different method in the next year if the natural one fails.

    Reply
    • Hi Jaye, I’m sorry that your apple tree is infected! Have you considered treating it with neem oil? That is all natural and often really effective.

      Reply
      • Hi,
        I saw that you posted this just 16 hours ago.
        I’m presently treating my one apple tree with neem oil.
        You say this works?
        Just spay-mist it, even the top branches?
        any advice?
        Thanks;
        Dave

        Reply
        • Hi Dave, I don’t have fruit trees myself, but neem oil comes highly recommended. You are definitely on the right track. Spray mist it. It’s important to cover the whole tree to kill the pathogen, so you should definitely be spraying the top branches. Try to spray the tops and bottoms of the leaves, so you will kill all of the fungi. Let us know how it worked if you have time!

          Reply
  2. My dwarf apple tree… The lower leaves I’ve noticed have a tiny pattern of white spots. It’s not powder, it’s in the leaf.

    Reply
    • Thank you for posting a picture of the leaves! I’m so sorry that your apple tree has this problem. You are definitely right that it is not powdery mildew. I can’t be positive, but it looks like insect damage to me. However, I am not positive and cannot suggest a particular pest that would cause those symptoms. I would recommend that you submit a sample to your county extension person. Here is the link to figure out the right office to contact.

      And if you do find out, please let us know. I am highly curious about what the culprit is and would greatly appreciate it.

      Reply
  3. Hi Helga,
    I just saw my apple tree leaves and little fruits have the white fungus today. The leaves and little apples look dred out and not healthy. How can I use the neem oil? Do I have to mix it with water? How much water and oil? Please let me know ASAO, so I can start tomorrow to spray it. Tomorrow will be raining. Is it okay to spray? I cut up lots of curly leaves today. Some little fruits are still good. It is a 4-variety apple tree in the pot. I have had it for 10 years. The flowers just finished at the end of April. I use organic Promix fertilizer of 9-16-16 for vegetables and fruit trees. I changed the top part of the soil with organic Promix vegetable and herb soil. Please advise. Thanks.
    MLT

    Reply
    • Hi MLT, I’m sorry to hear that your apple tree is infected with powdery mildew. Fortunately, it is one of those fungi that doesn’t kill their hosts.

      I admire your zeal, but I think it would be best to wait until the rain has stopped. It would be likely to wash the neem oil off the tree.

      I don’t have a label with me, but it should give clear instructions. I am pretty sure that you spray the neem oil directly from the bottle. The manufacturer will already have diluted it to an appropriate concentration. The tips I do have are:

      1) Don’t spray in the heat of the day.
      2) Don’t spray the flowers and when bees are around
      3) Don’t spray to the point where it will run off the leaves
      4) Try to treat the bottom and the top of the leaves
      5) Typically spray every 7-14 days unless the infestation is really bad, and then you can spray every 5-7 days.

      I hope that your treatments will be successful! If you have time, please come back and let us know how the neem oil worked.

      Reply
  4. Hi, same problem with my apple tree. I cut away loads of leaves, looks like I have to denude the tree to remove all the mildew. Could I avoid this by just using neem oil? Thanking you in advance. I live in Ireland.

    Reply
    • Hi Ann, I’m so sorry that your apple tree has such a severe case of powdery mildew. Neem is often used to treat powdery mildew. I can’t guarantee that it will work for you, though. Definitely spray both the top and bottoms of the leaves. Another option that is organic is Bordeaux mixture. It’s a mixture of copper and sulfur. Since you are in Ireland, I’m not sure of the brand names of the fungicides that I would recommend. There is a class of fungicides called sterol inhibitors that can be very effective. Two of them are myclobutanil and fenbuconazole. Your local garden center should be able to help you select a fungicide designed for fruit trees. Hopefully the neem will work for you. You will have to spray frequently to cure this infection. Please let us know how it works for you.

      Reply
        • I’m just in from cutting more leaves off the tree. Should I be gowned up like for corona? We are all so stressed now ????????

          Reply
          • Hi Ann, Again, I’m so sorry about your tree. Yes, these are stressful times. However, one good thing is that you do not have to worry about being gowned up while you prune your tree. Most plant diseases do not affect humans, and this is absolutely the case for powdery mildew. It is highly advanced at closely interacting with the plant. It is absolutely not a threat to you. Best of luck at the gardening centers!

          • Hi,
            My apple tree has same problem White powdery fungus, I am so upset for my tree. I cant go outside in my garden bcoz of hayfever, Please guide me

          • Hi Aroush, I’m so sorry about your apple tree. That is a distressing infection. If your tree hasn’t bloomed yet, you should cut off the infested twigs (when you can go out into the garden again). You will need to treat your tree with a fungicide like neem oil or one of the other ones described in the article. I hope that you will be able to cure your tree!

  5. Hi Helga… please can you help? My little apple is showing signs of mildew. If I spray with neem oil, will it affect the fruit in any way?

    Reply
    • Hi Sophia, I’m sorry your apple tree has powdery mildew. Neem oil should be perfectly safe to use and shouldn’t affect the flowers at all. Good luck!

      Reply
  6. I just identified that my orchard of 240 apple trees has Powdery Mildew. Many of the trees have fruit on them and the fruit looks okay. Every tree however has the mildew. Many of the new shoots from this season seem to be dead or dying even though there is still good growth and the trees over all look okay. The question I have is, what should I do now? It is early June and the weather is in the 80-90s and will soon be consitently in the 90s. We are in the drier part of Idaho. What treatment should I take at this time, into summer and then the fall. Thank you.

    Reply
    • Hi Ammon, I am so sorry that your whole orchard is infected with powdery mildew! I’m glad that the fruit look okay.

      Most of my advice is geared for homeowners, so I did some research with information for apple orchards from the University of Idaho. You can prune out the infected shoots, which won’t necessarily work, and doesn’t sound feasible for so many trees. I think your best bet is treatment with fungicides. Page 8 of the PDF recommends a series of sterol inhibitors, sulfur, and Sovran or Flint to treat powdery mildew. I hope this provides enough detail to help you!

      Reply
  7. I have a rose bush with powdery mildew about eight feet away from two paradise apple trees. Is there any chance the rose bush mildew will infect my apple trees? Thank you.

    Reply
  8. Hello, my apple tree is 2 years old and started showing signs of powdery mildew a few months ago. I didn’t realize it until a month ago and started spraying with neem. It doesn’t have any flowers or buds yet, just leaves. Should I just spray it, or should I pick off infested leaves and trim the stem/super baby trunk down below where I can see the mildew starts? I’m not sure how much would be too aggressive for such a young tree. Thank you!

    Reply
    • Hi Melissa, I’m sorry that your apple tree is infected with powdery mildew. You should definitely remove the infested leaves, so they won’t spread the spores. Spraying with neem oil is an excellent idea, too. It is usually effective against this fungus. You will need to keep spraying every 2-3 weeks until the new shoots start growing. Don’t stop if the weather dries up, because this pathogen will keep growing. I don’t think you need to trim the stem down. Hopefully that combination of actions will help stop the infection. Let us know how it goes.

      Reply
  9. Hi, My 11-year-old daughter planted an apple seed as an experiment during lockdown, and it is doing really well. Started to notice this powdery stuff on the leaves… how can I treat this please? It’s approx. 2-3 months old and has been kept in the house. Regards

    Reply
    • Hi Ailwyn,

      What a wonderful experiment! That is great that it was doing so well.

      Thank you for providing a picture! I’m sorry about the powdery mildew. There are various fungicides you could apply, but since it’s in the house and being tended by a child, I would suggest something with really low toxicity. I think neem oil would be a good choice. Be sure to spray the tops and bottoms of the leaves. That should bring it back to health. I hope it grows into an awesome tree!

      Reply
  10. Hi Helga, Thank you for this great article. My two apple trees have powdery mildew. I have 4 questions.

    1) If all the leaves appear to have the mildew, will it be okay for me to remove all of the leaves, so that only bare stems are left?
    2) Should I spray the neem oil all over the branches, stems and open cuts where I’ve trimmed the trees down for autumn?
    3) The article says copper sulfate and lime works to ‘prevent’ powdery mildew. Would it still help to apply even though I already have powdery mildew? And should I apply it after all the neem treatment, before or during?
    4) What natural substance can I use to clean the blades of my pruning tools to eradicate any spores left on there? I was thinking of white vinegar but I didn’t want to rust the metal blades from the acid.

    Thank you for your time.
    Best regards. Rachel

    Reply
    • Hi Rachel,

      Thank you so much for your kind words! We are delighted that you liked the article.

      1) Yes. You should remove all of the leaves if they have powdery mildew, or they will continue spreading the disease.

      2) Yes. You should spray all parts of the tree with neem oil, since the fungus can infect the whole tree.

      3) I don’t think it would help to use copper sulfate and lime at this point. I suggest that you just stick with the neem oil.

      4) You can use 70% rubbing alcohol. A lot of people use 10% bleach, but that can be hard on your tools.

      I hope your trees bounce back quickly! Let us know how they do in the spring.

      Reply
  11. I think I have this white fungus all over my huge apple tree. There is no chance that I can reach the high branches to spray it with neem oil. Is there anything else I can do? I love my tree and don’t like it hurting!

    Reply
    • Hi Joanne,

      I’m so sorry about your apple tree. That does sound like a difficult problem.

      Is there anyone you could put it in a container that you could attach to your house and spray the high branches? Arbico Organics makes a pressure sprayer designed for use with neem oil concentrate that should let you spray higher.

      Try that and let us know how it works.

      Wishing the best for your tree!

      Reply
  12. Hello, I have thirty apple trees in my backyard and every one of them is covered in white powered mildew. Will the the sub freezing weather kill the fungus or will I have to spray? I’ve been using neem oil (one a week) for the past two months, but the problem only seems to be getting worse. I’d appreciate any and all advice.

    Reply
    • Hi David,

      That sounds awful! I’m so sorry to hear it.

      The fungi will survive the weather and persist as a pathogen, so it is important to continue trying to control it.

      Neem oil is normally a good choice for this disease, but the fungus can develop resistance to the active ingredient in it. I would suggest switching to Spectracide Immunox Multi-Purpose Fungicide, which is available at Home Depot. This fungicide has been approved for food crops, so it should be a good choice for your apple trees.

      Hopefully, this will take care of the problem, but please let us know if it does not.

      Reply
  13. Hi I planted my first apple tree last year and I’m not sure of the variety at the moment. It got covered in fuzz and I assume it’s powdery mildew since I get that on my zucchini every year. I sprayed neem oil covering everything I could since it’s only a few feet tall. No results it just gets worse and worse. Now it’s spring and I’ve started a weekly regimen but I’m worried the mildew just won’t go away. It’s presence is still there even all through winter. Help.

    Reply
    • Hi Marissa,

      I’m so sorry about your apple tree! Powdery mildew does survive the winter on trees. However, it’s not usually fuzzy. I have never heard of such an extensive infestation on a tree, but I wonder if your tree could be infested with mealybugs. They are white and fuzzy. Could you possibly post a picture?

      Powdery mildew is a common disease on apple trees, but there are a large number of different species that tend to be specific for their hosts. I’m not sure the infection would have come from your zucchini.

      Neem is usually a good fungicide, but it doesn’t always work on apple powdery mildew. If you want to try a synthetic fungicide, my reply to Melissa above has a link for Spectracide Immunox (myclobutanil) that tends to be very effective against this disease.

      I hope that helps! If you have time, keep us posted about how your tree is doing.

      Reply
  14. Great article Helga; thanks. My Apple tree has powdery mildew on some branches. I also noticed that growths on the trunk also have powdery mildew. Ugh. A couple of questions:
    1. Should I start with neem oil? On the trunk too?
    2. Can the cuttings be put in the pickup can they use for compost, or does it need to go in the garbage?
    3. What do I clean my shears with?
    4. I have another Apple tree next to this one; different variety ( I don’t know what variety). Should I spray it too? It doesn’t have any sign of pm yet.
    5. I am in the Santa Cruz area fairly near the coast.

    Reply
  15. Helga, you are so kind to all your readers and provide great information. Thank you for such a great service. You helped me understand what was happening to one of my beloved Jonathan apple trees that I planted nearly 30 years ago. I trimmed infected areas today. Some ends of cut limbs had waxy white fluffy fungus coming from underneath the bark. I washed those with a rag wetted with water mixed with a little sulfur to remove the fungus, sprayed with Spectracide tar spray to hopefully seal the infection there (it’s too humid and hot now to spray with fungicide), and in a few days when it’s cooler I’ll spray with neem oil and perhaps sulfur. OK to use both alternately?

    Reply
    • Thank you for your message, Jeff! Neem oil and sulfur products can be toxic to plants if used in combination, and they should not be applied in quick succession either. A period of a minimum of 30 days in between applications is typically recommended. Sulfur also should not be used if temperatures are above 80°F.

      Reply

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