Arbutus: Arbutus tree

Discussion in 'Ericaceae (rhododendrons, arbutus, etc.)' started by Alison, May 26, 2003.

  1. Alison

    Alison Active Member

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    I have a ten year old Arbutus tree in my front yard that I have grown from seed.
    The leaves on it seem to get small black spots that eventually turn into larger spots and cause the edges of the leaf to go brown and/or yellow. The new leaves seem fine. What is this and how can I treat it?
     
  2. Douglas Justice

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

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    According to an article by Ralph Byther in the book The Decline of the Pacific Madrone (Centre for Urban Horticulture, University of Washington, 1999), there are at least 19 different fungi associated with leaf spots in arbutus. As the majority of these leaf spots develop in the autumn and winter, and the leaves are shed following development of the new growth, the spots are not considered to be a significant problem.

    However, if the leaves discolour and drop prematurely (i.e., before development of the new leaves), this could suggest a more serious problem, such as root rot or canker disease.

    By and large, as long as your arbutus is situated in full sun, in well-drained soil, with good air circulation (away from polluted air) and without supplemental water in summer (except under extreme drought conditions), it should survive handily. The incidence of disease in arbutus appears to be associated with other stresses (including drought, air pollution, compacted soil, shade, injury, etc.) as much as with the proximity to diseased plants. In other words, if there are no sick arbutus trees nearby and conditions are excellent for growth, your tree will probably not succumb to more serious diseases.
     
  3. I have a 3 year old arbutus tree in Steveston. The tree was growing quite vigourously untill a week ago when the tree's leaves on one side have drooped and the lower leaves have quickly died off. The dead leaves are covered in black spots.
    This seems out of charachter considering the immense growth the tree has had the last two years. Any suggestions?
     
  4. The arbutus trees on Eagle Island at Fisherman's Cove, West Vancouver ( 49 deg 12 N and 123 16 30 W) are dying. On this 15 acre island I estimate that at least 50 trees have died over the last 15 years. Over this period of time, all 6 Arbutus on my one acre lot have died. The dead trees vary in maturity from 4 to 40 centimeters diameter at the butt. Ititially the tree develops black leaves on selected limbs, the bark of which selected limbs, over a two-year period, then turns black and the diseased limb then dies. The disease progresses from limb to limb. Over an approximate 5-year period the entire tree will die. Pruning a diseased limb does not stop the overall dying process and in fact might speed it up. My observations suggest that the currently surviving arbutus are located in shady areas. I cut down one of my larger (20 cm butt) dead trees and noted that all of the heartwood at the butt was rotted out and infested with ants.
    Do you have any suggestions as to what the problem may be and if indeed there is a remedy?
    I look forward to your response.
    John Brock
    5838 Eagle Island
    West Vancouver V7W 1V6
    jsbrock@shaw.ca
     
  5. Douglas Justice

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

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    Interesting to hear a report on a specific island population of Arbutus menziesii, and your observations about the locations of surviving trees. Thanks, John.

    What you describe are the classic symptoms of "arbutus decline," which is postulated in the literature as being caused by mostly naturally-occurring, weakly pathogenic fungi, made more virulent by the predisposition of arbutus to disease, caused by urban stresses, especially root disturbance.

    Nevertheless, I'm convinced that much of the die-back we're seeing on established arbutus trees stems not from disease, but primarily from the complications of damage, competition, shading and especially, drought stress (we've had a run of very droughty summers). Typically, the most affected natural stands of arbutus are very dense, with poor air-circulation, internal shading and intense competition for resources (characteristic of rapid growth after clearing). And because this region is becoming increasingly urbanized, with more vehicular and marine traffic (marine traffic evidently accounts for a huge proportion of the pollution in the Fraser Basin air-shed), I would not discount atmospheric pollution as a contributor to the decline (one more stress).

    I think the reason your shaded trees are not as affected is that their roots are probably deeper and less exposed, and there is reduced evaporative demand on the leaves. However, as the shade increases, these plants, or at least their shaded branches, will succumb.

    What to do? I don't think there's anything we can do to save the existing trees, except, perhaps, to minimize human influence around them. We should avoid both disrupting roots and damaging above-ground portions of the trees (with pruning, for example), as any wound is an open invitation to disease causing micro-organisms. Interestingly, a friend of mine who kayaks around Gibsons has seen black bears foraging for fruit in the tops of arbutus trees on Keats Island (he should have told them they aren't helping the situation any).

    Irrigation of established plants is nearly always counter-productive because it encourages surface rooting (which is typically short-lived and considerably less resilient than deep rooting), and summer irrigation is worse, as arbutus are well adapted to our conditions (at least, where we find them growing naturally) and normally somewhat dormant in summer.

    We can plant more arbutus, as a previous correspondent in this thread has, to replace what we're losing, but there's no guarantee that these plants will survive the next drought or indeed, our well-intentioned meddling. (I suspect his plant was lost for the same reason most young arbutus are lost--by root damage from saturated or compacted soil conditions.) The natural succession on your island is probably (as elsewhere in similar places along the coast) tending toward open Douglas fir forest with a few scattered arbutus in the more inhospitable places. In other words, you can plant what you will, but the larger are the Douglas firs, the fewer arbutus will be able to survive around them. Neither species is particularly shade tolerant and resources are pretty limited on rocky ground, where both prefer to grow locally. Expect change.

    Finally, we can observe and record (as you are doing). This will ultimately give us a clearer picture of the magnitude of the changes taking place. Please let me know how things are progressing. Good luck.
     
  6. sue1

    sue1 Active Member 10 Years

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    I live on Gabriola Island, and have had to have a lot of arbutus trees cut down on my property, as they died, on were well on the way to dying. This spring in particular, the arbutus on Gabriola were loaded down with blossom, and the perfume sometimes overpowering. Perhaps they were stressed in some way, as I've never seen so much blossom. Some of the more healthy trees on my property I had cut in half, as the tree man said that they could leaf out again, somewhat anyway. He said they are like a weed. All the leaves that dropped over the summer were either black/brown, or spotted with brown. Hopefully I'll be able to save some of these strange trees on my property.
     

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