Victoria, BC (on Vancouver Island)

Discussion in 'VCBF Neighbourhood Blogs' started by wcutler, Mar 2, 2009.

  1. Douglas Justice

    Douglas Justice Active Member UBC Botanical Garden Forums Administrator Forums Moderator VCBF Cherry Scout Maple Society 10 Years

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    Very nice. No obvious brown-rot-caused "witch's brooms," which are so common on spring cherries in Vancouver. It makes me wonder if this plant is on its own roots.
     
    Last edited: Feb 1, 2021
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  2. Acerholic

    Acerholic Paragon of Plants Forums Moderator VCBF Cherry Scout Maple Society

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    Good morning Douglas, can I ask why witches brooms are common in Vancouver ? Perhaps compared to other locations.
    I found this comment by you fascinating.
     
  3. Douglas Justice

    Douglas Justice Active Member UBC Botanical Garden Forums Administrator Forums Moderator VCBF Cherry Scout Maple Society 10 Years

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    Note that these are not the phycoplasma-related witch's brooms we associate with dwarf conifers. In cherries the witch's broom is an ugly proliferation of ragged branches caused by a systemic infection by brown rot disease. Brown rot infection is common on susceptible species like Prunus itosakura (syn. P. subhirtella) and is facilitated during mild, wet weather. In Vancouver, we can have rain without a break for days and days in the early spring (and in autumn and winter).

    The problems usually start with a flower infection (blossom blight), which spreads into the surrounding tissue, killing back the tender vegetative growth (twig blight) adjacent to the flowers. Perennial cankers in the twigs produce spores for subsequent infections. Later regrowth from behind the original damage may become infected if the rain persists, or avoid infection and extend for some distance if the weather is cool and or dry, only to be infected in a subsequent season. The result is a rat's nest of dead and live branches.

    Grafted cherries seem to be most at risk. This is probably (I'm definitely speculating here) because of increased susceptibility due to stress related to differential growth—the two species, P. itosakura and P. avium, pushing growth at different times or rates. The particular P. avium cultivar used as grafting stock in British Columbia is 'Mazzard F12/1', which is very vigorous (well matched to 'Kanzan'). On the other hand, perhaps P. itosakura cultivars like 'Autumnalis Rosea' are just
    too prone to infection because of the wet conditions here.

    We at UBC Botanical Garden have been experimenting with a variety of cherries, growing brown-rot- and bacterial canker-susceptible cultivars on their own roots to compare with grafted plants. Initial results look promising, but it's still early days.
     
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  4. Acerholic

    Acerholic Paragon of Plants Forums Moderator VCBF Cherry Scout Maple Society

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    @Douglas Justice, thankyou Douglas for the very informative reply. I have learnt a lot today about brown rot causing witches brooms in Cherries. I wonder if the environmental changes we are all witnessing the world over is the main contributing factor with this problem. Though here in the UK we are experiencing very warm but very dry Springs these last couple of decades, so your theory of climatic effect on Cherries will probably not be noticed as it is in Vancouver.
     

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