Arbutus: Blackened Arbutus

Discussion in 'Ericaceae (rhododendrons, arbutus, etc.)' started by Uberwench, May 24, 2006.

  1. Uberwench

    Uberwench Member

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    Can anyone tell me if the rumour is true that arbutus are dying in epidemic numbers from a disease that causes branches to go black and die? What is this blackening phenomenon, and how can I help my arbutus trees that have it?

    Many thanks!
  2. Rima

    Rima Active Member

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    Eastern Canada
    I know nothing about the rumor, but if it's true, it's very unlikely you can do anything because it's obviously a virus or something with no available treatment - or it would have been implemented by now, I would think. Google for more info.
  3. Daniel Mosquin

    Daniel Mosquin Paragon of Plants UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    Vancouver, British Columbia, Canada
  4. Lazz

    Lazz Member

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    Yes, indeed, this rumour sadly appears to contain much truth.

    The reference given above for 'Madrone Problems in British Columbia' is just one chapter from a book 'The Decline of the Pacific Madrone' which can be accessed in its entirety from the University of Washington website:
    'The Decline of the Pacific Madrone'

    Gathered together from an arbutus synposium in 1995, it is perhaps chapters 5 ('Some Observations of Madrone Diseases') and 7 ('Diseases of Pacific Madrone') which are most relevant.

    Arbutus are susceptible to a wide range of opportunistic fungal infections, most of which are relatively harmless and just a natural part of its life-cycle. It's a tough tree and survives on the margins in the most inhospitable terrain. When weakened by changes in environment, however, these infections may often prove fatal.

    There is a delicate balance of factors involved here.

    It loves light and sun, for instance, but if it loses branches and foliage, or surrounding shade is suddenly cut-back, trunk and bark becomes very vulnerable to sun-scald and weakened in the face of infections which it might otherwise shrug off easily.

    Leaf fungi are quite normal and only become serious threats if there is a lot of repeated defoliation involved exposing the tree to other problems. In recent years there has been a noticeable spread of these other problems - mainly due to the three killer pathogens Phytophthora cactorum, Nattrassia mangiferae, and Fusicoccum aesculi.

    Phytophthora cactorum is a serious root-rot.
    If you water your arbutus, then you are only encouraging this root-rot.
    Don't do this.

    Nattrassia mangiferae is a very nasty piece of work.
    Under normal circumstances, the tree will protectively callous over the infested area, but if the tree is experiencing a bunch of other problems at the same time, then it can likely succumb and die.

    R S Hunt, in the chapter referenced in the preceding post, calls Nattrassia mangiferae a 'native' fungus. However, as far as I can make out, it actually originated in the Indian sub-continent and seems most likely to have been accidentally imported to the Carribean by a human host during Victoria's reign and gradually spread from there. I am told that there is now no uninfected part of arbutus habitat anywhere in North America. It is recently reported even in Greece amongst Arbutus unedo and Arbutus andrachne. So it's definitely spreading. And so the future for the genus could be decidedly bleak.

    Fusicoccum aesculi causes branch die-back.
    Dead branches look as though they have been burned.
    It doesn't attack healthy vigorous trees. But for those already weakened by the other fungi or by water stress - look out!

    Any of these problems can make the impact of otherwise quite ordinary leaf fungi more serious. Reduction of foliage means reduction in photosynthesis. Reduction in foliage means greater vulnerabilty to sun-scald damage. Lowered photosynthesis and increased exposure to sun-scald means greater risk of killer fungal infections and reduced ability for a tree to survive them.

    I suspect that fire management regimes have also played a powerful role in allowing these problems to combine and gather speed.
  5. M. D. Vaden

    M. D. Vaden Active Member 10 Years

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    Beaverton, Oregon
    There are a few "boo-boos" that Arbutus has to deal with.

    It's much nicer when they don't get a problem. I don't mess around with the ground near ours.

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