Read This If You Grow Japanese Maple

Now that I have your attention… This post is about a common bacterial disease called Pseudomonas syringae, which frequently affects Japanese maples yet is relatively easy to control. It is often misidentified as Verticillium wilt, as both cause tip dieback. The Pseudomonas bacteria form purply-black stem discolorations, which is the result of a toxin produced by the bacteria which kills cells. Twigs, branches and eventually the entire tree may die. Older and stronger growing trees are less susceptible, as are some varieties. Do not prune maples in the fall (especially in the Northwest) as this disease enters any wound and is encouraged by wet, cool winters. Any cut, at any time of year, should be sealed immediately with a liquid sealant.

Control is three-fold. The first is keeping your Japanese maples strong, healthy, and damage-free. The second and third are related: If you can keep your tree dry during wet and cold periods, that is half the battle. The other is chemical control, which is by copper sulfate or similar bactericide. Consider using Phyton 35, a systemic bactericide. Top spray and bottom drench is recommended.

If you have problems with this disease, try a chemical drench after repotting or after heavy root work, perhaps with ZeroTol. And if you live in an area with wet, cool weather in the fall through spring, seasonal prophylactic spraying is a sharp idea.

Clearing away leaves and especially seeds of maples—like bigleaf or vine maple—is essential after leaf fall as these commonly planted landscape trees are frequent carriers of the disease. Keep leaves and moss away from trunk bases, too.

The purply-black tissue damage of the Pseudomonas bacteria shown on this branch is typical of the disease.

Discolored stem damage above and below a pruning cut (seen as a white stub) where the bacteria likely entered the Japanese maple.


  1. Ram says:

    Howdy Michael

    I have a few questions.

    When you say “bottom drench” I assume that means to water the tree with the chemical mixture.

    Second question is about frequency, how many times and at what time of year would you reccomend top spray and bottom drenching japanese maples?



    • crataegus says:

      Yes, ‘bottom drench’ means water the roots with the chemical solution.
      Water the top too, until everything is dripping. That is important– with any of these contact chemicals, they need full coverage to be effective. So get underneath branches… into bark, everything.
      As for frequency, most bacterial issues are problematic during your wet period, so whenever that is, spray a few times during those seasons. If you’re spraying preventatively, try a few times in the winter. If you have problems, try more frequently and change up ZeroTol with a fungacide/bactericide which will give you more control. Copper sulfate works. If you have fungal problems or suspect that, and want to control a broad spectrum of diseases, Subdue is excellent if expensive… For small collections I’d recommend the simpler/cheaper controls like copper and lime sulfur.
      In the Northwest, I spray from fall through spring as that is our wet period and bacteria are most active then.

  2. Bruce says:

    Michael, thanks for this information. It’s always cool and wet here and I have pretty much given up on Acer p because of this problem. But I’ve never understood why the ones in the ground are not affected. Acer b (trident) have never had this problem. They are that much more hardy it seems.


  3. Steve Moore says:

    Thanks, Michael. I posted a link to this article, with appropriate attribution, on my own blog — then linked that to FaceBook. Sometimes technology ain’t so bad!

  4. Chris Glanton says:

    Michael, I read this when you posted it and never heard of it. But 3-4 wks ago, one of my JM’s had this exact thing on it. (An air layer from last yr). The tree is inside my overwinter hoop house. I cut off the infected part, but can’t treat it as the soil is damp. What would you do here in Jan? Should I treat my other JMs too? I can always spray, but not the drench.

    Thanks for bringing this up! I’m new to JM’s and never heard of it before.

    • crataegus says:

      Many fungicides may be used as a drench, regardless of soil moisture. I would try a spray regardless. As for how often consult which product you’re using. The ZeroTol I use as a preventative spray several times in the dormant season.

  5. Chris Glanton says:

    Thank You Michael. I’ll hop right on it with the Cooper and see if I can track down ZeroTol. Again, Thanks!

  6. terry davis says:

    Michael, Some comments on black twig on maples. A few years ago I got a an Mikawa Yatsubusa from Mountain Maples (who did not make good on it). It was infected, and it took out the plant, an old Kotohime, and several japonicums before I got it under control. I understand it was epidemic in Oregon. Every “Shaina” I have ever seen has had it, and I could never keep one alive. A local nursery had ten trees several years ago and every one had lesions. I don’t know if any of the other dwarf red forms are less susceptible. Dissectum seems to be vulnerable, too, but not as badly. Susceptibility recognition is likely a key ingredient.
    I had heard of using a potassium permanganate drench, and this was also recommended for all Rosacae.

    • crataegus says:

      I will try the potassium permanganate drench, I have not yet. There are definite ranges in the susceptibility to this disease. Pseudomonas will affect some Japanese maples and not others. I grow a couple of seedling unnamed ‘varieties’ that are so strong that I have yet to have any affected by it. The native vine maple is susceptible. Trident maple less so. I think that strength and natural vigor is a factor here.

      • Bruce says:

        Interesting and crucial information. I think along with this, tool sterilization needs to be addressed. When I asked our local plant pathologist he said the most effective solution is a 50-50 mix of Lysol CONCENTRATE and water. Of course there are commercial solutions but they come in large quantities. He further said that although Clorox is commonly thought to be a good sterilizer it’s not that effective on a broad range of pathogens.

  7. Bruce says:

    This disease also took out a couple choice, old Pieris japonica’s. Broke my heart.

  8. terry davis says:

    Speaking as a chemist, I would not combine ZeroTol with any commercial organic treatments, as it would likely react with them. Followup in a few days miught be better.
    Subdue is a very narrow-spectrum fungicide, only active against pythium or phytophora (the two most-common root pathogens). I am told it is so narrow that it the company almost marketed it in combination with other fungicides (In fact, in DrenchPak, it is combined with Cleary’s 3236, which is how I use it). Ppseudomonas is a bacterium, so Subdue shouldn’t work with it (but if you say it does, stranger things have happened). In its proper use, it is extraordinarily effective, and it has literally saved plants for me. I have heard that Subdue is supposedly phytotoxic when sprayed on the foliage of some plants, e.g. azaleas, but I haven’t been able to confirm that. I have also had a lot of luck with Bonide ROse Rx, which is a combination (non-smelly) insecticide and fungicide.
    I have used Fire Blight spray (streptomycin) for black twig, and am not sure if it works, but it makes sense, since it is an antibiotic. I have been loath to get copper in the soil, as it is so broad spectrum, it may damage mycorrhizae. Your input? I would think permanganate as a drench might have the same problem. This was for Rosacae (sp. cotoneasters), though, which may not be so dependent upon mycorrhizae. The specific Treatment for Pseudomonas respiratory infections is erythromycin, esp. in some of it its more potent varieties (Clarithromycin), so maybe this would work.

    • crataegus says:

      Thanks for your comments!
      I must have mis-written; I don’t combine ZeroTol with anything, only meant that I use it in combination as a control. I don’t mix it physically with another product. I do like it, as I used to like lime sulfur. But lime sulfur is messy and smelly and I prefer ZeroTol because it does about the same thing. I wish it had some residual effects, though.
      Actually when I researched this a while back the Arborists that I talked with said that Pseudomonas is controlled with many of the simpler fungicides like copper. Even though it is a bacteria. That surprised me too.
      I don’t use copper drench, but know people who do. I don’t use copper wire as a tie down wire because of its strange reactions in the soil. Roots tend to not grow in the area around copper wire, I guess it gets concentrated and toxic perhaps?
      Again, appreciated-

      • Chris says:

        Damn Michael, I just lost sev. branches to this darn dz again. It’s been very wet here this summer, esp. last week. Nothing’s drying out. Luckily I now have Zerotol. May I ask, you use the same dosage as the chojubai of 1.25oz/gal both as a drench and spray?

        I don’t know why, but every yr. I’ve lost some branches to this darn dz. So strange too given this yr’s been very healthy for me, not one pest or dz other than the nematodes and pseudomonas.

      • crataegus says:

        Zerotol has uses, but as many limitations. It’s topical, and so when pseudomonas is already inside the plant it won’t help you. Cut away what is affected, and then try a systemic like Phyton 35.

        For other situations, Zerotol may be used as a drench at 2 oz. per gallon.

  9. Dustin Hoang says:


    If my maple experience this disease, should I repot the tree then drench with bactericide?



    • crataegus says:

      If you suspect there is damage in the roots and you’ve got the tree at the right time of year, yes, you may wish to repot and clean out the infected area. You do the same if you suspect it in the branches—cut it away and disinfect and then seal it.

  10. Paul Pashley says:

    Pseudomonas releases a protein that also lowers the plants’ ‘anti freeze’ properties, making plants more susceptible to die back from freezing temperatures. Another reason to keep infected plants under shelter away from the cold & damp conditions of Winter.

  11. Christine says:

    I’ve lost several JMs to this disease, or V. wilt. Not sure which, now. But without the black stems, perhaps the wilt. Nonetheless, I’m Pinning this post because it breaks my hear to lose any of my trees. With 127 and most in pots, it’s always a fear. Thanks for the info!

  1. […] This article was originally published at Crataegus Bonsai […]

  2. […] Do you grow Japanese maples? Micheal Hagedorn (Crataegus Bonsai) has an article on detecting and controlling Pseudomonas syringae bacteria, titled Read This If You Grow Japanese Maple. […]

  3. […] Michael Hagedorn has posted an article worth a read by any grower of Japanese maples. You can find it at: […]

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