Please advise on Bacterial Canker on Interspecifics


I did spray it with copper before cutting although not after cutting. Didn’t think of it at the time. Not really an option now. Using latex paint was recounted (as suggested by the Amish) in one of the old threads on gardenweb to treat girdling by rabbits. The paint is supposed to retain moisture so that the cambium doesn’t dry out and help prevent infection by sealing the wound.

I agree it’s ultimately the plant that decides its fate. All I can do now is try to keep it healthy.

I am no expert here but Titanium-Dioxide is a main ingredient of the paint and supposedly has anti-microbial properties when stimulated by light so there’s that at least. Just from a quick search:

I’ll update later in the year about tree health so maybe this experiment will be helpful to someone else in a similar situation someday!


In one paper by MSU with cherries they suggested spraying before and after when pruning. Canker’s are so easily infect cherry trees.[quote=“dwn, post:21, topic:4688”]
I’ll update later in the year about tree health so maybe this experiment will be helpful to someone else in a similar situation someday!

Yes that would be very helpful!


Antimicrobials in paints can be harmful to trees and are not recommended in guidelines about painting bark white (a common practice to protect trees from southwest injury and borer and even vole damage). I do not know about the specifics of whether all paints with anti-microbials are harmful or how damaging they are but university guidelines consistently steer growers from applying any paints containing them to plants.


I use pruning seal on damage like that to help the tree maintain internal moisture. That may not work as well as I think it does.


Yes, it is used in almost all paints, it’s the basis for white paints, exterior and interior, latex and oil. It makes white whiter, is not toxic to us, covers stains even in wet mode, an amazing molecule. I think concern about exterior paint is because they add other antimicrobial products, but I’m not sure? I never studied it much. A product called microban is added to exterior paints, and the warnings are for this product, and other similar products not Titanium-Dioxide (TiO2).


There are some anti-microbial paints which are now being recommended for grape wounds, to prevent eutopia dieback. See for example

See the last line in the treatments where these wound sealers are recommended:

In addition to the fungicides labeled as pruning-wound protectants, consider using alternative materials, such as a wound sealant with 5% boric acid in acrylic paint (Tech-Gro B-Lock), which is effective against Eutypa dieback and Esca, or an essential oil (Safecoat VitiSeal).

Here is an article one avocado canker that shows the best thing is a certain fungicide (fosetyl). Copper and tree wound paint beat the control (no coating at all) but did not prevent new cankers.

To me these results state that if you have the right chemical, with or without including it in paint, for the particular tree/disease type, you might get some good control. The paint vs not paint has an impact but its not large - the canker size was 1/3 the size with tree paint vs the control, but there was still a canker.

If there is no major disease spores for 14 days it sounds like there is no great risk - after 2 weeks the avocado wounds were resistant. So if it is a season where no spores are floating there is no big need to do anything. And, it probably depends a lot on what disease, different diseases would benefit from different treatments.

I found one more study on honey locust:

It shows the coatings not having so much effect on larger trees – statistically significant but less significant than the above avocado study. Maybe it is more beneficial for smaller trees and vines.

Here is an article on an oak wilt. Apparently they recommend painting over recent pruning wounds if this nasty beetle is present as they go after new wounds:


Very informative, thanks. Plant pathology is a very dynamic field. Extremely interesting to me. I took one class at MSU but that was last century and as Farmer Fred rule number 7 says, “everything you know is wrong!” often applies!

Yes, like a band aid to keep the beetle out.
Oak wilt is a very concerning disease for me having numerous oaks on my property. I love those trees! Pruning sealant is suggested if you trim healthy oaks. Nothing is black and white, only shades of grey.
Farmer’s Fred rule number 6 WHAT’S OLD IS NEW AGAIN.


I was referring to house paints that put antimicrobials in the formula to prevent mildew and such. What is the paint DWN applied? Is it a botanical formula?

I hadn’t heard about this “tree paint” and it must be a new product because it is not widely recommended in extension guidelines I am familiar with, like this one.

When you are keeping insects from wounds, which is rarely the case, wound sealants have always been recommended.


Here is a page that I think summarizes things well:

Basically for standard pruning wounds there is no benefit to painting and there could be drawbacks. If you are fighting a disease, the evidence is more murky, there are some cases where treatments have been shown to help.

Personally, I just cut out my cankers and leave it at that. But, I wouldn’t be surprised if there was a coating down the road which was beneficial to lay on afterwards.


Good article. That’s a nice site, lot’s of interesting material. In that article this is mentioned:

“Some studies have also shown that wound dressings have some benefits
when used to prevent infection from the fungal spores of various
pathogens. Wound susceptibility of Prunus spp. to Leucostoma spp.,
the pathogen causing a perennial canker disease of stone fruits, varied
by time of year and that the application of shellac was beneficial in
reducing infection.”

Funny as using shellac was something my great grandfather would have used.
Farmer Fred Rule Number six, WHAT’S OLD IS NEW AGAIN. On the radio, one radio host mentioned using shellac, he said orange shellac was best. I noticed it’s hard to find, and it is dewaxed. I would you wanted that, guess not? Shellac is made from the resin of the Lac Beetle larvae.


I love Farmer Fred already :heart_eyes:
I understand the reluctance to ‘coat’ the wood and possibly promote ‘secondary’ infections favored by trapped moisture. Another approach to consider is to spray the bark tissue with either colloidal silver which is bacteriostatic, or something like essential oil of Eucalyptus (diluted). Several applications would likely result in absorption into the wounded area and thus reduction in vulnerability without smothering the tissue (so to speak) and possibly trading one pathology for another.
Just sayin’


OK, so still no word on the nature of the paint already used and whether it might be a problem.

Scott, I’m really not sure of the conclusions of this particular guideline, partially because it is not at all assertive and more because the source is not guidelines from a part of a university involved in commercial fruit production such as this one, which also advises not to paint after removing fungal canker from peaches. .

When I see a guideline from a university to commercial peach growers recommending painting of wounds when cutting out any kind of canker I will believe that research is reasonably conclusive and should be recommended.



This is the discussion from gardenweb where I read about using paint to seal the wound when a tree is girdled:

I remember reading somewhere else to look for (interior) latex paints without an anti-mildew additive. So when I painted the tree in this thread, I specifically checked to make sure it didn’t advertise it’s anti-mildew properties. Whether it was anti-mildew and just didn’t advertise it, or whether the ingredients themselves are - I don’t know.

I agree that seeing a university recommendation for paint would be more conclusive. But if the Amish use it then it must provide some benefit and be reasonably cost effective as far as home growers are concerned.

I’ll report back about how the tree does.


If it isn’t the paint that is warned against using then I’m sure you are fine. When you said it was anti-microbial I guessed that it was probably the stuff that is allegedly phytotoxic.

My perspective of tree care is a bit different than the average manager of their own small orchard. I don’t have time to do anything that isn’t necessary to their care because I’m charging for my time.

Incidentally, I think when a tree is girdled there may be reason to seal the wound, not so the tree heals more quickly but to try to help reduce evaporation form the wound while it heals. I don’t think this has been put to research and it is just a hunch on my part and probably not worth the effort of typing it out.


Thanks for that tip. It’s worth a try.
Considering the various opinions on paint or don’t paint, it may be that the solution depends on the specific injury, the health of the tree, the weather, etc.


Sometimes I think we fail to see the obvious. Our immune system works well, but we can die with many infections without help from antibiotics. Sure trees can defend themselves, like any living organism. But obviously many problems the trees cannot overcome and need help. It is rather disheartening that so little is studied about plants. I find it surprising more info is not available.
What kills bacteria/fungi, kills bacteria/fungi anywhere. We just need to avoid hurting the tree.
Creating a sterile field around the wound is a very good thing. As long as we can do it without harming the patient!


Not all trees have a ‘fighting chance’. Trees are made vulnerable like people are. And we can’t avoid hurting the trees - poor soil, or nute uptake (roots), sun/temp/wind/vermin or mechanical (pruning) trauma may compromise the ability to repair. I’ve found it useful to look at reducing the tree’s vulnerability.
Silver is used for burns to reduce vulnerability to infection when the skin is traumatized/absent. It is cheap to make, but bark may not absorb it like softer plant tissue does - just dunno. I’ve used it to prevent damping off. EOs on the other hand have very small molecules that are known for easy penetration, but are very concentrated and must be diluted. I’ve used this to reduce fungal issues in the high tunnel over the winter.


I also little faith in studies, and anything from academia. Coffee is good, coffee is bad, no it’s good again, Wait! It’s bad. It’s getting old! Same with about any subject matter of study. Best figure it out yourself.


Well. I think studies are helpful. But then, I’m a nurse and feel pretty confident in the Scientific Method. It’s part of our scientific “sorting out” process. Do scientists hit the nail on the head with the first study (or 2nd, 3rd, or 4th?) Not always. Are all studies non-biased? Of course not - it is our duty to do our due diligence to ascertain bias or influence, as well as a well-conducted study. But it’s the process that is important, and with that, we gain knowledge. I think a healthy combination of being informed via well-done/conducted studies and learning by empirical experience is the happy medium. There are a fair amount of well-done studies within the world of botany, plant cellular/molecular biology, just not so easy to find. Alan has that in spades. I trust Alan’s judgement and advice, as he keeps himself well informed, plus has many, many years of empirical experience out in the field. And, as an aside, most all of the recent studies involving coffee have all been very favorable. So, I still have my BIG cup of coffee every morning without worries :slight_smile:


That’s fine not to trust WHO, I think they are over-reactionary, frankly. They also just published a statement regarding pregnant women, and that they should not consume ANY alcohol.

But, that is only ONE source, and one preliminary study. So, we cannot toss out the baby with the bathwater, here. The Scientific Method is still sound. After all, it has provided us with life-saving vaccines, drugs, and methodologies we use every single day. You simply cannot paint all Scientific Method with one black brush based on preliminary study. That would be like saying you had a terrible nurse take care of you last time you were in the hospital, so now you do not trust ALL nurses. I would be offended at that blanket judgement statement, as I happen to think I’m a pretty good nurse. So, when you say, “I don’t trust these people”, you cannot lump all Scientific Method in with WHO. Or the scientists that published this one study, that uses a LOT of qualifier adjectives. That’s silly. For goodness’ sake, if you drink too much water it will kill you. Take the information, and assess it for it’s value as it applies to you, and use it wisely. Wait for more studies that can replicate the results.

If you read that article, it states, “In fact, coffee is in the same 2B category as cell phones because of evidence that drinking coffee could be associated with cancer of the large bowel. On the other hand, coffee was also recently linked to a lowered risk of fatal prostate cancer, so go figure.” So, preliminary findings, more studies to follow that will reveal more info. That’s how it works, Drew. Do not lose faith in a methodology that has provided us some very, very valuable information to lead better lives. You should know this, you’re in the medical field.

So, I’m going to put my moderator “foot” down, here, which I don’t think I’ve ever done on this forum, and ask that we stop the debate about the Scientific Method and its validity. I think this is rather pointless, and it is taking away from this thread’s original intent. If you would like to debate the Scientific Method, there are better venues than our forum to do so. I hope you understand, Drew.

Patty S.