[Archivist]

Nectria (PDF of archived thread)

[Brittany Kordick]

We are knee-deep in dormant pruning and dismayed to see the degree to which nectria cankers have pervaded our orchard after years of essentially non-treatment due to our assumption of cause by fireblight. And since we’ve been so successful in treating fireblight cankers by scraping and saturating them with AgriPhage, we’ve increasingly left any large cankers we find during pruning and treated them in this fashion . . . but now we’re finding that many or most of these are, in fact, due to nectria colonization, rather than fireblight (or who knows, perhaps black rot, or any number of pathogens capable of forming cankers). Of course, wherever possible, we’ve gone back to removing cankers, but when it would necessitate removing a particularly precious limb or removing a significant section of the central leader, we’ve been going wobbly and just excavating the canker, hoping to experiment with treatments (hand saturation with concentrated lime sulfur, hand inoculation with Lalstop G46 — fight a sap fungus with a sap fungus, hoping for outcompetition, plastering with neem butter or biodynamic paste, etc.), as well as irritating the healthy live tissue surrounding, hoping to spur the sealing process to get on with it.

So as we make these hard decisions, we’ve become really interested in understanding more about the nectria cankers themselves, particularly the extent to which they may encompass and parasitize living tissue beyond acting saprophytically on dead tissue. Indeed, one of the most insidious aspects of nectria is this ability to colonize as a sap fungus, before turning parasitic and infecting living tissue. Because of the rampant colonization of certain varietal blocks, I am also interested in the idea of systemic treatment of cankers via trunk injection, but since I understand the canker to be comprised primarily of dead wood, I must question whether such treatment, assuming an appropriate material could even be identified, as well, as the proper timing to apply it, would be worthwhile at all.

We understand that nectria-cankered trees end up in something like an annual give-and-take battle with the fungus, where the fungus never actually dies off; the tree just lives with it. This concept reminds me a lot of Dr. Srdjan Acimovic’s research surrounding fall and winter development of fireblight cankers, where the trees effectively wall off the fungus, but in doing so, can actually protect and preserve the cankers to future detriment. But nectria does not derive from bacterial pathogens and usually starts as a saprophytic fungus on dead wood . . . so we are wondering, if the tree does seal off a nectria canker, unlike with bacterial fireblight, has it effectively cured itself of that particular canker? I don’t believe the fungus would be able to sporulate the next season, but again, I’m not sure to what extent it could still potentially harm living tissue within the tree or simply survive within until . . .

All this has really made me wish for a better understanding of pathogenic cankers in general, to be able to better identify their sources and assess possible action steps. For example, when is dead wood just dead wood? Or even if one did feel like a large canker was inactive or sufficiently hand-treated, in a nectria-stricken orchard like ours, where residual inoculum and reinfection is likely in the short term, is exposed dead wood always to be treated like a liability? I remember reading an article about nectria that detailed the risk “almost always associated with “pulled stems” left when harvesters remove apples, but leave stems in the trees.” I’m wondering if perhaps we created the perfect storm for nectria in more ways than one in our orchard: lots of fireblight inoculum in the form of dead wood dating back years, subsequent mis-treatment as fireblight, but also, after a couple of years of heavy pruning of very large limbs as we catch up in vigorous blocks, leaving tons of unusually large cut ends on a given tree for inoculation as dry, “dead” wood that remain unsealed for several seasons following.

Don’t really have anything new to report — obviously, we’ll see if our efforts at controlling nectria pay off, come mid-June, when we typically see drastic die-back. I think organic orchardists of all stripes necessarily have a higher incidence rate and tolerance for retention of cankers in their orchards (whether we should or not) when compared with conventional growers. This is really just a food for thought update, reflecting the need for a thread looking closer at the differences and similarities of various common pathogenic cankers with regard to identification, assessment and treatment.

[Steve Dagger]

Thanks for this post, Brittany. It helps put in context some of the canker issues I’ve been dealing with for years. I’m not as far along in identifying and trying to treat cankers in my orchard as you though I have modified my pruning some and excavated a few cankers on very young trees to prevent them from becoming girdled. I hope others will use this and related threads to share their experiences.

Pommes de Terre Acrea
Intermountain West Region