Fungicide resistance?

[cmiller]

Hello Don,

I've read your website pretty thoroughly now, because i think you've nailed what is wrong with all my trees, too. This year brought a very wet, cold, extended spring and so the damage to the trees is pronounced. Because the damage is so extensive, and among so many species, i turned to Google images and found the splitting bark that characterizes this disease, which i've described as "cat claw marks". For a long time, i thought to protect the tree boles from my cats with wire cages, which did no good, of course. The google images found on your site describe the damage here and on other trees in the vicinity - and in the "sale" aisles at the nurseries! - just about perfectly. I thought perhaps i'd brought it into my area by buying sale trees, but i've noted similar symptoms on inspection of my neighbors' trees, as well as others up to 40 miles away; it's a widespread problem, for sure.

Your synopsis of most affected tree species fits well, too. In my case, the first casualties were some mountain ash. I put it down to bad soil. I replanted, amending as i went. Then the birches died, including one that was about 12' tall, whose girdling black band about 2' above the ground was so weak as to make the tree start to bend to the ground, such that i propped it up until it died. All my maples are exhibiting the very typical split bark and cankering, broomy branching with many limbs growing downward, and wilting leaves. My lone ginkgo is exactly as you described...no bark lesions, but just a few leaves this year, with the downy white hairs on them. Prunus of all kinds are severely affected; apples and pears are a mixed bag. Also i note that leaders often die, and that there is a pronounced sucker growth at the base. Curiously, ants are swarming on the trees in proportion to their observed lack of vigor: sicker trees --> more ants. Locusts are less affected, and bur oak show no observable effect, which in interesting in that SOD disease would seem to prefer them.

Now i'm looking at your fungicide choices and wondering if you've updated that at all, since it appears the website was created in 2008 and the forum has seen little traffic so far.

My concern is what i've been reading about risk of resistance to fungicides. I've been emailing with an orchardist who recommends using more than one fungicide at each spraying, from different groups, to ward off creating pathogen mutations resistant to a particular fungicide, thereby eliminating its usefulness. I'm wondering if you've had any experiences with that, or with other fungicides you've tried besides the ones listed, or any other information you can share; e.g. i've been wondering what the effect of using something like copper might be on the disease, but would rather not reinvent the wheel if you've tried it. Any further information you have in this area would be most welcome.

I can't thank you enough for putting such a Herculean effort into the website. I've looked at other Phytophthora species and their effects, and without being a botanist it seems clear to me that the set symptoms you describe are indeed not matched by other set of symptoms i've investigated on the Net, but they match my experience of the disease nearly perfectly. I wouldn't have known what the next step was without your "white canker" work. Maybe they'll name it after you when they "find" it, eh?

Thanking you in advance for your consideration,

Colleen Miller
Stevensville, Montana

[Don Peters]

Thank you for the feedback Colleen. This website gets a fair number of visitors, but for some reason people don't post in this forum (except for spammers - I'm wildly popular with them for some reason!).

You're right-on when you say a very wet spring brought on more symptoms. White canker is a fungal disease that thrives on moisture either on the bark of a shrub or tree or just under the bark (in the green phloem nutrient transport system). Its growth is more vigorous in these locations. Propagation via spores takes place on the bark surface.
 
Your symptom observations on a variety of trees agrees exactly with what I'm seeing. For example, white birch trees, which were fairly common around here in years past, now are becoming a rather rare sight - especially healthy birch trees. Most seem to be dead or dying. Yet no one seems to be noticing it. I'm guessing that nobody is noticing this because the die-off is taking place over a several year period. This disease is usually not a quick killer.
 
What I REALLY wish some people would do would be to look at the leaves and twigs and bark of these diseased trees/shrubs under a 400 power microscope so they could actually see that the inner bark is being eaten away by a fungus, as if it is being dissolved by an acid.
 
My fungicide effectiveness studies still stand. However, my tree-care company recently increased prices dramatically. So I'm now experimenting with treating my trees and shrubs myself. There is no way I can reach the top to tall trees, or most trees, so I'm trying another approach: I mix the systemic fungicide I found effective (Propiconazole) with a chemical that helps it penetrate the bark, and then spray this mixture all over the trunk, from ground level to about 5' high. It's called a "trunk drench". I just started testing it this summer, and so far it's very effective. Trees that were previously dying are now nice and healthy. But since this treatment doesn't kill the fungus (according to the fungicide manufacturer, it just keeps the fungus from building cell walls), you have to repeat treatments every 3 or 4 weeks. I'm probably going to post more details in another note, e.g., exactly which trees & shrubs I treated and exactly what effect it had.
 
Yes, using a variety of fungicides would be ideal. Unfortunately, I don't have the means of evaluating a wide variety of fungicides - I can only evaluate what commercial tree care companies use. Plus, some fungicides may have harmful effects on pets, plants... or us! I was hoping that others would test other fungicides and post the results on this website. But nothing so far. I guess people in general still don't really believe there is such a thing as this white canker fungus. Even our state university plant pathologist doesn't believe it!

Oh, I should say that during a wonderful tour of Mt. Auburn Cemetery, in Cambridge MA (which has a huge variety of trees), it was pointed out that some beech trees were in a state of decline (sure looked like white canker to me), and that Cornell was trying an experimental treatment. I got the name of the researcher there, called him, and found that they were doing "trunk drenches" using a chemical call Agri-phos, along with a bark penetrant. I was surprised to find out how similar our treatments were! As far as I know, since they are still in a testing mode, nothing about its effectiveness has been published.
 
I don't know if the name "white canker" will stick or not when it becomes more widely known. But it needs some name until we come up with a better name, or until some lab identifies exactly what kind of fungus it is. Right now, most experts are dubious about this disease when I say that it attacks almost all trees and shrubs to some extent. Strangely, none of the experts I've contacted seem to have an interest in looking into it. When pressed, they say they "don't have the time" to review the evidence!

For those who really care about the health about their trees and shrubs, I hope this website helps.
 

[cmiller]

Don,

I just received a pint of propiconazole and will spray my trees as soon as the wind/rain/lightning stops, i'm not evac-ing for range fires (!), etc. I've been looking all over for a source for Pentra-Bark or Breakthru, by themselves, as i have the propiconazole in hand. In further reading about Sudden Oak Death, i note that Agri-Fos (correct spelling) plus Pentra-Bark is sold on eBay together, for about $250....quite a chunk of money to try it out to see if it works, considering that you found one of the fungicide trials ineffective. ("Agrifos", with no hyphen, appears to be an unrelated fertilizer company.)

To this end, i contacted Bill Stringfellow, a name you've possibly encountered if you've been reading about Phytophthora diseases, because his contact number was listed on a site that lists Pentra-Bark as a product. Pentra-Bark is made by Agrichem, an Australian company, with which Mr. Stringfellow is closely aligned. He seems especially engaged in discussions about Phytophthora ramorum, aka Sudden Oak Death. They use Agri-Fos and Pentra-Bark to treat that with some success. We discussed the possibility this is an outbreak of SOD in my area.

I expressed my doubts that this is P. ramorum on three counts: the spore images i've seen online for P. ramorum were lemon-shaped, and i read them described as such, whereas these "white canker" sporangia are more like flattened spheres, wouldn't you say? Secondly, the infected bark on trees with P. ramorum looks weepy and has a higher width:length ratio than the dry, split, expanded bark on our trees. Thirdly, root rot is a feature of P. ramorum infection, at least in some trees, whereas my infected trees readily sprout from the root collars. Trees i've removed due to continual die-back seemed to have quite adequate root systems. I've actually uprooted dead-looking trees, seen a healthy-appearing root system, and stuck them in the ground at the edge of the property, where they've sprouted from the root collar. They don't look good but they are still throwing up shoots years later. Your Rose of Sharon rising from the dead comes to mind. 

At any rate, Mr. Stringfellow is sending me some samples of Agri-Fos and Pentra Bark to try on these trees, in exchange for telling him about you, this site, and sending him the photos and PDF i prepared for our ag extension agent, to whom i took samples of tree bark, limb die-back, and wilting leaves two days ago.

I asked if mixing the propiconazole with Agri-Fos would decrease the chance of fungicide resistance developing, and he agreed it would. I've found a few sources online for fungicide resistance management, and here's the clearest table i've found so far from Purdue Extension (for pome fruits, but i'm assuming the basis for mixing different classes of fungicides still holds):  www.ces.purdue.edu/extmedia/bp/bp-72-w.pdf  If i find a better table later on, i'll share it.

We talked about application rates and timing. He suggested spring and fall bark drenches, rather than monthly. Are you treating monthly just because you got in the habit from foliar spraying monthly, or do you notice an uptick in symptoms one month post-drenching? Or maybe you haven't had enough time to decide yet? If semi-annual treatments would suffice, it would certainly be a more supportable spraying schedule, as well as decrease our use of chemicals, and lessen the strain on our mad-money budget! 

It sounded like Mr. Stringfellow intends to contact you, and says this is timely as there is an industrial-strength tree-huggers meeting in Chicago soon, which he will attend. He also said that considerable money is being thrown at the research on P. ramorum. I guess that's either an indication of the severity of the disease or alacrity of the fundraisers, lol. We can hope that this can either be folded into that knowledge base, or create another area of interest.

I so hope this disease gets the attention it ought to be receiving. More and more people are starting to note how many trees are dying, and it's not just due to harsh winters. I have Chinese Elm kicking the bucket now...a tree you could only kill previously by driving a stake through its heartwood. Another neighbor came over to discuss this a couple hours ago, after noting my hoophouse and thinking i might know things. ha ha ha...

Don, is there any way to attach files here? As you can see, i'm a hot-linking fool, and i'd also like to attach my PDF and pictures within my post to add to your public service on this issue.     

[Don Peters]

Pentra-Bark doesn't cost that much, actually. I found a few sources on the Internet, but ended up buying mine from treecaresupplies.com for $24 USD per pint. It was worth it to me to get the satisfaction of treating my trees and shrubs myself.

Actually, I'd describe the white canker sporangia as roughly spherical, milk-white, about 50 micrometers in diameter, and almost always having two distinct lobes, sometimes with a touch of yellow between the lobes. They rest on a stalk that is only about 5 micrometers high and a few micrometers thick, so this stalk is very difficult to see as it is almost always hidden by the sporangia above them.

I wish I could treat once and be done with it I began  my treatment study by having a commercial lawn & tree care company do my trees. Of the four fungicides they tried, only Propiconazole and Mancozab were effective. And after about three weeks I noticed the white canker symptoms returning. Plus, these fungicide treatment company directions say to treat every 3 weeks or so. They're right! According to the directions, the fungicide doesn't kill the fungus, it just prevents it from making new cell walls. Its up to the trees to keep up the battle. A healthy tree can often live for many years with a white canker infection. After all, a well-seasoned fungus doesn't want to kill off the host that feeds it!

Yes, you can post pictures in this forum, as you can do in most forums. In fact, I just posted a note on our red maple trees dying, and that posting contains two pictures. Limit your picture size to 1024x768 pixels. The catch is that you have to place your pictures on some website, and then reference the pictures with a full URL (use the Preview button to verify you have it right). So you'll have to find some picture hosting website. Same with PDF files (although there is no size limit).

[cmiller]

Pentra-Bark ...ended up buying mine from treecaresupplies.com for $24 USD per pint.

Thanks for that. I will DIY this as i do everything else out here in the boonies.

Actually, I'd describe the white canker sporangia as roughly spherical, milk-white, about 50 micrometers in diameter, and almost always having two distinct lobes, sometimes with a touch of yellow between the lobes.

Thanks for the correction. I thought the indentation you'd mentioned in the centers meant the whole sphere was flattened. I suppose i'll have to break down and buy a microscope...eventually.

I wish I could treat once and be done with it I began  my treatment study by having a commercial lawn & tree care company do my trees. Of the four fungicides they tried, only Propiconazole and Mancozab were effective.

Agri-Fos was first lauded as a cure, but downgraded to a renewable treatment. Still, if it works based on bark drenches twice a year...i like that. I remember thiophanate-methyl from the table of effective fungicide treatments you tried; did you find it ineffective after a while, or what?

Yes, you can post pictures...the catch is that you have to place your pictures on some website.

Ah, that's what it appeared. I've not done that yet. Too bad climbing these learning curves doesn't burn any calories! 

[cmiller]

I wanted to finish up with my experience with the trees.

I submitted samples to the ag extension agent, which were transferred to MSU, Bozeman, for examination by a researcher there. The extension agent and a retired plant pathologist came to look at my site last week. The plant pathologist said she's been on your site, Don; her name was Cynthia Ash. She is not too fond of you and refused to look at your site, though i urged it and mentioned the microscopic images. 

Cynthia seemed fairly convinced my trees are suffering from Verticillium wilt, so took more samples to attempt to culture it. I tend to think that's not right, since the same wilt on which she's an expert, Verticillium albo-atrum and Verticillium dahliae, should also have affected my tomatoes and potatoes just feet away, which were not affected.

The researcher in Bozeman dismissed the lengthy account in a CD i'd sent along with the samples, which gave a history of the site, soil type, the species affected, and so forth. With no evidence, she refuted my explicit statements about having planted them at the proper depth, though Cynthia admitted they were planted at the proper depth. The researcher said i'd fertilized too heavily and probably poisoned them with Dicamba, all of which is rubbish. There's no mention in her report of ever viewing the samples under a microscope.

Another woman from my community garden group who also submitted samples along with mine was told the bark damage to her trees was "mechanical". Like she has a 3'-tall lawnmower....

There's more, like their asking me why i just don't switch to junipers instead, but it's too disheartening to go into. Suffice it to say, i completely understand your frustrations with the authorities after getting my hopes up that these scientists would be impartial and thorough.

I ordered Pentra-Bark from your source, and applied propiconazole in a trunk drench last Thursday.

I called Bill Stringfellow about whether he'd sent the samples he intended. He'd gotten my email with the mailing info and this site's URL, but hadn't acted on it. He said he was going to be in the NE before long, and that he might possibly contact you when he is. I heartily recommended it. Let me know if he follows through, would you?

FYI: i called Stringfellow also to get the proportions of PR to propiconazole per gallon. Bill told me to use 2-3 oz. of propiconazole and 2 oz. of PB per gallon of water. I'm curious what ratios you are using with the Agrifos, if you don't mind telling me. I've worked out that i'll be spending about $30 a month to protect my trees, if this even works.   

[Don Peters]

Ah, yes, Cynthia Ash. She came to look over my trees and shrubs in 2005. She seemed very nice during the visit. But I later had some doubts about her diagnosis, and called to discuss them with her on the phone. She seemed very upset and somewhat angry that I would dare to question her, and she then refused to spend any more time with me discussing the subject! I was somewhat taken aback by this as I come from an engineering and science background, and try to seek out as much evidence as I can before coming to important conclusions. So it's no surprise to me that she "refused to look at your site". As for me, I'm willing to look at all evidence and to see where it leads.

Yes, I too am mystified by so many "experts" in the field giving a shoot-from-the-hip diagnosis when they have little to go on. It gives me the impression that plant pathology is more like a black art than a science!  I like the statement made by the late tree expert Dr. Alex Shigo, who said something like "I listened to the trees, and I listened to the experts, and they disagreed - I decided to believe the trees".

I'd love to hear from Bill Stringfellow and discuss this disease with him. I'll let you know if he contacts me.

As I said in another posting, I'm not testing Agrifos, as I'm just now completing my testing with Propiconazole and Pentra Bark. I don't recall the mix ratio at the moment, but I believe I still have enough for two more treatments of my yard (about 25 shrubs and trees), which might do me for the season since I apply every 3 weeks or so. I think one cost me $12 and the other was $30, so that would be about $40-50 per season. Our local lawn and tree care company will do the spraying for you for about $100 per treatment, so maybe that would be something like $700 per season. That's fairly expensive (at least for me). But, you do also get insect protection thrown in when they do the treatment. On the other hand, I find that my combo treatment makes the trees healthy enough that they seem to be able to better defend themselves against insect pests, so I'm not seeing a need for insect control on my treated trees and shrubs.