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Bacterial Canker in Prunus Species

Posted by Todd Parlo 
Bacterial Canker in Prunus Species
January 18, 2013 10:08PM
A bacterial assault was waged this past season in the northeast.

Here at the farm, we are having trouble with plum trees. The plums in our orchard are relatively young and generally healthy and vigorous. They flower beautifully and are surrounded by pollinators, yet they bear no fruit. As we pruned this winter, we noticed some bacterial canker on the branches, characterized by gumosis and orange mold-looking spots. In the spring, the flowering stems were hit with blossom blast immediately after flowering. The blossom blast caused rapid brown dieback, often overnight. These symptoms were showing up on plums, cherry plums, and Hanson’s bush cherries, all closely related Prunus species.

After some research, we learned that these symptoms stem from the same bacterium- Pseudomonas syringae. This bacterium has over 50 pathovars, affecting a wide variety of plants including tomatoes, maples, wheat, mangoes, kiwi and more. Prunus stone fruits are affected by the P. syringae pathovars syringae (causing blossom blast) and mons-prunorum (causing bacterial canker).

P. syringae is present in the air, water, and on plant surfaces all around us. This bacterium causes water to freeze at high temperatures and is responsible for a majority of frost damage in plants. It also plays a big part in the Earth’s hydrological cycle. When airborne it serves as a cloud condensation nuclei and ends up in raindrops and hailstones.

Here in the orchard it’s a big nuisance. The pathogen lands on healthy stems, overwintering on healthy dormant buds. Because it causes ice to form at high temperatures it creates severe frost damage. In the spring when the damaged tissue thaws out, P. syringae colonizes that tissue. It colonizes especially quickly in cool, wet conditions. The pathogen will kill flowering stems immediately after flowering (blossom blast), move into the wood and create cankers. The pathogen will multiply and overwinter in these cankers, spreading further in the tree the following season.

There are no good treatments for this bacterium and prevention is the best strategy. Remove diseased stems, leaves, and cankers immediately to prevent it from spreading. Healthy trees can fight off the bacterium more successfully so invest in the health of your tree from the start. Make sure that the soil around the tree is full of microbes and that the tree is not stressed due to lack of nutrients or water. However, be sure not to over-fertilize. Too much fertilizer will create an abundance of succulent shoots, which are favorite overwintering spots for for the P. syringae bacterium. Prune the branches to ensure lots of air flow and quick drying of the tree’s surfaces, which reduces opportunities for the bacterium to colonize.

Foliar sprays that inoculate the shoots and leaves with probiotics are another way to invest in the health of the tree and help it fight off the bacterium. We are going to experiment with these sprays to improve the health and production of our plums.

Several extension agencies recommend spraying with copper, a common treatment for fungal and bacterial diseases. While there are some organic copper sprays available, they are harmful to beneficial populations and it is expensive to maintain full coverage of the tree. Full conventional orchards go so far as to spray with methyl bromide, but we do NOT recommend this treatment as it is highly toxic and not getting to the root of the problem.

Experiment with different varieties of plums! Plums tend to be very capricious- flourishing in one micro-climate and suffering in another- even when they are fairly close by. Talk with local growers and gardeners to find out what varieties do well for them try them on different areas of your property.

There’s nothing like a the deep flavor and juicy goodness of a plum in the summer, so we will continue to experiment and learn so that we can grow them successfully in our orchard.

Bacterial canker. 2009. [www.which.co.uk] (June 11, 2012)

Eastwell, Kenneth C. et. al. 2005. Field Guide to Sweet Cherry Diseases in Washington. Washington State University Extension. [cru.cahe.wsu.edu] (June 11, 2012)

Kennelly, Megan et. al. 2007. Psudomonas syringae Diseases of Fruit Trees. Plant Disease. [www.agroquimicosgaspar.com.ar] (May 31, 2012)

UC Management Guidelines for Bacterial Canker on Plum, 2009. University of California Davis. [www.ipm.ucdavis.edu] (June 11, 2012

(This report was written by Sarah Claassen, a friend and apprentice at WHNO, 2012)

Walden Heights Nursery & Orchard
Zone 3 in Vermont

Edited 1 time(s). Last edit at 01/22/2013 06:48AM by Michael Phillips.
Re: Bacterial Canker in Prunus Species
January 18, 2013 10:39PM
The references to the bacterium causing water on the trees to freeze at a higher temperature are intriguing. This phenomenon is not noted in the references you posted; can you point to sources? I find the concept interesting because, in general, dissolving anything in water tends to lower the freezing point, not raise it. Certainly water needs a nucleus to start to form ice, but I would have thought that there are abundant nuclei on the surface of trees outdoors without invoking a specific bacterium as responsible. (I can see how it would be an excellent ploy on the part of the bacterium, though, if it could manage to induce freeze damage, because it would permit it to invade the damaged tissues, while healthy intact tissues would resist. Go Pseudomonas!)
Re: Bacterial Canker in Prunus Species
January 18, 2013 10:47PM
Sigh. . . Pseudomonas syringae is a difficult one.

It is ubiquitous. Seemingly benign most of the time, likely a beneficial factor in the earths various cycles (as you noted in the hydrological example for rain fall) and one that has a genuine Dr Jeckyll and Mr. Hyde when it comes to its life in the orchard.

We had to remove all of our Santa Rosa plums, cherry and peach trees (2 dozen total trees) as a result of it coming on strong 4 years ago.

I thought we had gotten past this little bugger. . . or maybe I had just put it far enough out of my mind because last spring a late freeze which coincided with our primary bloom on our apples gave Pseudomonas syringae a direct access point to damaged blossoms and fruit spurs. We lost 85%+ of our fruit set last year to it. Broke my heart. Some of the damage extended to a handful of young branches, most specifically on the Spitzenburg variety (planted next to both Calville Blanc and Ashmeads who had the blossom cluster damage, but nothing on any branches).

It is a common topic at UC Davis and within their IPM classwork.

Notes from the UC IPM Management Guidelines for Bacterial Canker (Pseudomonas syringae):
Bacterial blossom blast is difficult to control. When possible, use overhead sprinklers to prevent freezing. Monitor temperatures wherever freezing is most likely to occur in the orchard and turn on sprinklers when the temperature drops below 34°F (1.1°C). Turning on sprinklers before the initial drop in temperature helps avoid the damage that results from evaporative cooling. Uniform coverage of all tree parts to produce a combination of water and ice is essential. Finally, keep sprinklers going until temperatures are well above 32°F (0°C) and the danger of frost is past.

The ill timed unprotected freeze seems to be the spark that lights this potential powder keg. That was surely the case with our experience with it last year.

Btw, I agree . . . Once you have had a perfectly ripened plum in summer, it is a heavenly memory you never forget.

Best of luck, keep the forum posted of your efforts!

Gopher Hill Apples
Zone 8 in California
Re: Bacterial Canker in Prunus Species
January 19, 2013 07:42AM
The freezing is due to the bacterial cells acting as nucleation sites. The link is below- it is an interesting read, and interesting to note what happened in Michigan in 2012 is identical to what cycled here in Northern Vt. The last few years we had little trouble with blast except for bush "cherry".

"Ice nucleation is a trait whereby PSS cells can catalyze ice formation at temperatures only slightly below freezing. Pure water can supercool significantly below 32 degrees Fahrenheit without freezing. However, the presence of ice-nucleation active PSS cells enables ice to form at temperatures of approximately 28 F or below. Once ice is formed, it rapidly propagates through sensitive tissue such as flowers, causing wounds that facilitate bacterial entry into the tissue. The severity of frost damage plays a critical role in the occurrence of subsequent wood invasion and canker formation..." (quoted from below article). It goes on to say that the temperature/pathogen cell number present ratio is the determinant in an outbreak.


document title is :" Bacterial canker, ice nucleation, frost injury and blossom blast in sweet cherries" , from Michigan State
Re: Bacterial Canker in Prunus Species
January 19, 2013 05:01PM
Indeed a most interesting read. But I am not wholly convinced that the good Dr. Sundin has proved his point. If I understand correctly, he is saying that essentially all blossoms are infected to some degree with Ps. sp. Said Ps. serve as nucleation sites, (makes emminent sense), and the more Ps cells there are, the more nucleation sites there will be, (equally reasonable). The problem, I would suggest, is that he fails to evince any actual evidence of a relationship between numbers of Ps. and freeze injury. It also implies a unique role for Ps. as ice nucleation sites. But cells are filled with all sorts of solid lumpy things which can serve as nucleation sites, (chloroplasts, membranes, nuclei, nucleoli, ribosomes, ...) I will grant that increasing the number of such sites by introducing extra ones, (bacterial cells), may logically increase the likelihood of ice crystal formation. But logic does not always apply, (eg. this logic is predicated on the assumption that the likelihood of crystal formation is linearly related to numbers of nucleation sites - the more sites, the more likely crystals will form. And I am far from certain that this is true. Indeed, I think it more likely that there is a threshold effect - there is some minimum number of sites needed to initiate the process, but adding more sites above this point has no effect.) So, I would like to see a graph of numbers of Ps. cells per blossom vs. extent of freeze damage, as evidence of the purported relationship.
None of this actually matters in practice, of course. According to the author,all blossoms are infected, (to varying degrees), there is nothing you can do to alter this, although the point he is trying to make is that inhibiting the multiplication of the bacteria in the warm spring weather prior to a freeze may, by reducing nucleation sites, reduce the likelihood of injury - a notion which, as I have suggested, he has not convincingly proven.
Re: Bacterial Canker in Prunus Species
February 24, 2013 08:24PM
I have been having the same troubles with bacterial canker in the hybrid plums at MOFGA's orchard in Maine. I first noticed the problem in 2011 when it showed up as blossom blast, and as Todd mentioned, it seemed to happen overnight. It only showed on a couple young limbs of two plum trees (Toka and La Crescent). I thought about pruning out the limbs when I noticed it, but thought that would open to the tree to further infection, so I decided to monitor the situation for the season and saw no other signs. The following winter I pruned and burned those limbs.

Last spring, the blossom blast came on strong on the same two trees, so I pruned and burned right then and there. Later in the season, I notice more cankers developing on these two trees with the associated gummosis. The cankers were only on one and two year old wood. I decided not to prune immediately. So my plan this winter is to cut and burn both of these trees when I prune in the next couple weeks. Removal seems like the only option to prevent spread of the disease.

What's troubling is that the disease only showed on these two trees (Toka and La Crescent), but not on any of the other ten or so varieties. They are all densely planted on 6' - 8' spacings and rows 20' apart, so a chance to spread should be high. The two trees are the largest in the plum block and were the most productive until 2011.

I've read that bacterial canker can be systemic in the tree, but will not survive below ground in the root system. So I am thinking that after I cut down the trees, they will send out numerous suckers from the root system this year, and I could graft on to a sucker next year. The trees are too dense to try to dig out roots without disturbing others on either side, and this would be a way to get a new replacement tree.

Any thoughts?
Re: Bacterial Canker in Prunus Species
February 24, 2013 09:40PM
CJ, from experience I would say that the pathogen will find them all, and will be a real problem some years, but hopefully not all. We had blast in Toka, LaCrescent, Aldermann, Underhill, Pembina, Waneta, Superior and all the seedling P. americana and besseyi. I cannot find records on Bounty(P. nigra). Greengage was clean. For most of us near a richer environments containing varied native species, these diseases are likely to be present. For stone fruits, pss and others like black knot are sure to be around when choke and black cherry or wild plum are present. Cutting back the trees and regrafting will only buy you time I suspect. I hate to make it sound dismal, but striking it from the area is unlikely for most of us. The answer will have to be with managing the disease, hopefully learning to live with it with some degree of acceptance. It is also possible some of the species we really want to grow won't be worth it for everyone.

Walden Heights Nursery & Orchard
Zone 3 in Vermont
Re: Bacterial Canker in Prunus Species
February 25, 2013 12:34AM
I am into an area where I really have neither expertise nor experience. But, my observations in my orchard of multiple apple varieties strongly suggests markedly varying varietal sensitivities to various insect attacks. There are obviously varying sensitivities to scab between varieties. Might this issue with canker not be similar - variable sensitivity by cultivar? (If this be the case, perhaps the solution is to simply grow a different cultivar, rather than fighting an implacable enemy.)
Re: Bacterial Canker in Prunus Species
March 11, 2013 03:21PM
I don't have any practical experience observing this disease but was curious if any one has observed any difference in pss infection or severity in highly susceptible cultivars on differing rootstocks or self rooted trees. It would be an easy premise to test by adding a few self rooted trees in among the same infected cultivars to see if the improved tree nutrition/health resulting may offer increased resistance to the disease pressure. This premise arrived at because biodynamics says a grafted tree is always over fed or under fed by mismatch of rootstock and scion. And Gary Couvillon(sp) of U of GA (at the time: late '80's approx) doing work with self rooted peaches for machine harvest "annual" meadow culture , had data showing that self rooted trees had significantly higher uptake of calcium thus may have better resistance to disease due to calcium strengthening the cell walls. Don't know if other nutrient uptake was assayed, but it could be that it is all a matter of how efficiently the rootstock can extract nutrients if they are available or how well the scion utilizes them to induce resistance since most cultivars until recently have been selected for fruit qualities, not for disease resistance.

I historically(since the 60's) used the English liquid seaweed extract Maxicrop. It was said to cause frost protection even when applied only a few hours ahead of frost. I later heard that it was effective this way because it "got rid of" bacterial nucleating sites for the ice crystals. And as I recall the implicated bacteria were Psuedomonas. I never saw actual research on this and don't know how the Maxicrop effects this in such a short period. If I find my copy of, Seaweed in Agriculture and Horticulture by T. L. Senn; I will look for any reference to it. Meanwhile you may want to try it at bloom and season long for better nutrition.

BioRational Resource
Re: Bacterial Canker in Prunus Species
June 12, 2018 07:21PM
There is bacterial canker on the trunk of a bare root cherry we planted last fall. I understand the bacteria is systemic, but I would still like to try a localized biodynamic poultice of clay I dug and refined, a little soil from the rhizome of an old nearby Russian Olive (Eleagnus Augustifolia), kelp emulsion, and self fermented lactobacillus. I'll apply the poultice over the darker area and periodically spray over the poultice with regular holistic foggings. The canker is in a very early stage, but based on the dialog and Todd's experiences, I don't have super high expectations. I am hoping that our extremely dry climate and the ability to utilize aggregated online horticultural experience will allow the tree to continue to survive. Otherwise the tree appears healthy, its leaves are a deep green and perky and it is situated in a very sheltered location (which is one of the reasons this is a bummer, I want to use this particular microclimate for a cherry). Thank you all for this great posting of information.

Karn Piana
Zone 7 Semi-Arid Steppe
Northern New Mexico

Edited 1 time(s). Last edit at 06/13/2018 03:16AM by Karn Piana.
Re: Bacterial Canker in Prunus Species
June 15, 2018 09:33PM
Follow-up and interesting behavior in Pseudomonas syringae:

As a follow up and after having read more I actually do feel optimism with this tree: it's newly planted, and I think we are building a powerful and diverse system around it which will hopefully allow it to get established and thrive. I'm not even totally sure that the tree has bacterial canker: it may be that the tree suffered a minor injury to it's trunk and is undergoing some kind of localized healing crisis. The tree itself is very perky and appears to have great vitality and vigorous growth.

For discussion: I am very interested in the role of sunlight in the Pseudomonas syringae life cycle. Does it induce gummiosis in order to sequester sunlight? Is it getting something it needs by doing this? Here is a very interesting graphical outline showing that Pseudomonas syringae "rapidly inhibits" photosynthesis and CO2 production in it's victim.

A thought: enclose the tree in a plastic structure and flood the enclosure with higher concentrations of CO2..

I have to run, but that's the general idea...

Karn Piana
Zone 7 Semi-Arid Steppe
Northern New Mexico
Re: Bacterial Canker in Prunus Species
June 26, 2018 08:41AM
There is an interesting update linking to a research paper using UV light in the red spectrum to effectively combat P. syringea posted in the forum here.

Karn Piana
Zone 7 Semi-Arid Steppe
Northern New Mexico
Re: Bacterial Canker in Prunus Species
April 06, 2021 11:22AM
I posted about my noob success with using tree paste on canker in the peach canker thread, has anyone else tried treating with this?
Re: Bacterial Canker in Prunus Species
April 06, 2021 02:12PM
I'd be interested in the results. I've been using poultice's of various sorts for years - embedded w/ parasitic nematodes, pure neem, various repellents. I've started adding these to tree paste as well. I've seen generally good results on trees damaged by borers, string trimmers, tractors, voles, deer, etc. of course the damage can't be too severe, but it does seem to help. I think the additional beneficial microbes via manure, 500, or other source could only be good in fighting P, syringae and other limited-systemic and surface diseases. So, I'll be following this thread closely.

Mike Biltonen, Know Your Roots
Zone 5b in New York
Re: Bacterial Canker in Prunus Species
April 06, 2021 08:26PM
I will post any observations I have, but really we’re just looking at a couple of trees here and even in the community orchard we are currently planting we only have a dozen or so peaches, (our other prunus don’t seem to be affected so far,) so off we want real numbers someone else would have to do some experimenting or share their experiences.
I was inspired to try this after seeing positive results from the poultice experimenting that the holistic orchard prompted me to try with our butternut canker, then I was only using healthy compost/clay. My tree paste is kind of a hybrid of the bd approach and the whitewashing I read about in historic orchards but I worry about the lime hampering the biology in there so this year I reduced the proportion. But maybe it was the lime doing the trick and not the rest of the mambo jumbo, I’m self taught and really going by gut here, those of you who understand the micro might be able to give suggestions that would lead to more Fruit full experimentation


SW Wisconsin zone 5a/4b
Homestead/community orchard
2ish acres with half planted in 2018-2019 with heritage apples, alternating b118, antonovka, and seedling roots
Second half planted 2021-22 with plums, cherries, apricot, peach, pears, etc...
SE slope, trees are planted in contoured berms
Native prairie species for all ground cover

Edited 1 time(s). Last edit at 04/07/2021 12:29AM by Prairie Sundance.
Re: Bacterial Canker in Prunus Species
April 11, 2021 06:31PM
Hi Dan,
I'm just reading this forum and saw your post, years after the fact. I'm intrigued by your tidbit about spraying liquid seaweed (Maxicrop) on blossoms before a freeze. Do you recall the application rate you use? Looking at Maxicrop's website, their application rates seem to assume direct watering instead of spraying. (I'd also be curious about any other info you feel like posting on this.)

Zone 7a in West-Central MD
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