Rhododendrons: dieback on old, large rhodo?

Discussion in 'Ericaceae (rhododendrons, arbutus, etc.)' started by eric_r, Mar 22, 2008.

  1. eric_r

    eric_r Active Member 10 Years

    Messages:
    60
    Likes Received:
    1
    Location:
    Vancouver
    We have a large rhododendron that must have been planted many years before we moved into this house in January 2003. In the past year or two it has developed what looks like dieback on some of the branches. Some of the branches I have already cut off; others have died since then.

    The previous owners (who were here nine years before us) did not do much to look after any of the garden before we moved in: the garden was quite neglected and overgrown before 2003, but the rhodo seemed quite healthy until a year or two ago and has always bloomed profusely every May.

    In trying to guess what could be causing the problem I have come up with the following possibilities, none of which I am completely sure of:

    1. We had the perimeter drainage around the house redone two or three years ago and the digging around the base of the house near where the rhododendron is could have (a) damaged the roots (but the dieback would have to be a very delayed reaction) or (b) changed the drainage pattern in the soil around it. We also had the sewer line replaced, for which there had to be digging right under the rhodo. (But this was about four years ago.)

    2. I have watered the rhodo occasionally in the summer, but not as much as other plants. If the drainage around it is poor, the summer watering could have caused a root fungus.

    3. The gutters on the house above the rhodo have a concave corner that is very prone to getting filled with leaf drop from large cedars that are near the house. In the winter rain tends to spill off that corner of the roof onto the ground near the rhodo. I had thought, however, that having redone the perimeter drainage, any such water would be taken away into the drainage system. If this is the problem then it is a mystery that it didn't happen with the previous owners who generally did not keep on top of house maintenance.

    I have posted several photos of the rhodo that attempt to show the dieback. I also posted one photo of a R. siderophyllum that is growing near it. We got the siderophyllum two or three years ago and originally had it growing in a very tough spot under two cedars. I moved it to this spot last November (I think) and as the photo shows, it is blooming very well. Should I be concerned about having the siderophyllum close to the affected large rhodo? Even closer to the affected rhodo is an Olga Mezitt that we planted two or three years ago, which also is very healthy.

    I would appreciate any advice about or identification of the problem with the affects rhodo.
     

    Attached Files:

  2. Ron B

    Ron B Paragon of Plants 10 Years

    Messages:
    20,668
    Likes Received:
    548
    Location:
    WA USA (Z8)
    Rhododendrons are prone to water molds destroying their roots, this is one of the main things that comes up in discussions of their pests and diseases and often manifests as branch dieback. Like most trees and shrubs they are also on the menu for honey fungus, which sends rhizomorphs up onto the crown and lower trunk, and if successful killing the entire top from that point up - and thereby providing itself with more dead wood to decompose.

    There are also water molds that attack the stems above the ground, old hybrid rhododendrons that look like they have rheumatoid arthritis are afflicted with stem phytophthora. There is also the new sudden oak death, this is a water mold that attacks the leaves and can produce mystery leaf burn etc. You need laboratory methods to identify that one and indeed most of the others (honey fungus can be recognized using visual inspection, the rhizomorphs and mushrooms both being comparatively large and conspicuous).
     
  3. Liz

    Liz Well-Known Member 10 Years

    Messages:
    1,526
    Likes Received:
    2
    Location:
    Victoria Australia [cool temperate]
    I on the other hand am loosing them to very dry weather and being unable to water them well (restrictions). I will be pruning out the die back and hopefully they will reshoot when the weather improves. One of my main ones has been in situ since at least 1955 when the house was first built. I also have problems currently with the pest that attacks the underside of the leaves and makes them go silvery. Same problems with azaleas. My other query is are you sure that is a rhodo in the picture. If it is I apologise but for me it looks like something else??? The last picture is one but the first 2 ??

    Liz
     
  4. Ron B

    Ron B Paragon of Plants 10 Years

    Messages:
    20,668
    Likes Received:
    548
    Location:
    WA USA (Z8)
    The way the damage to the one is in the upper part only it could have gotten frozen during the winter, the outer ring of green leaves being the part that was under snow during a critical period.
     
  5. eric_r

    eric_r Active Member 10 Years

    Messages:
    60
    Likes Received:
    1
    Location:
    Vancouver
    The dieback actually seems to have occurred mainly during the summer, and given that the last few winters here have had absolute minima that have been higher than earlier years, I somehow doubt that the damage is from cold temperatures.

    I gather that some varieties of rhodos are more susceptible to water molds than others. I never have tried to identify what kind of rhodo this one is but your comment suggests that it is some kind of hybrid. Is there any website that has information on what species types are more resistant to water molds? (Most of our other rhodos are species rather than hybrids.)
     
  6. eric_r

    eric_r Active Member 10 Years

    Messages:
    60
    Likes Received:
    1
    Location:
    Vancouver
    Yes, I'm quite sure it's a rhodo. Ron B., who also replied to my post, and who seems to be very knowledgeable, did not seem to doubt it was a rhodo from the picture.

    If it blooms again this May I can post a photo of the flowers, which may help identify it.
     
  7. Ron B

    Ron B Paragon of Plants 10 Years

    Messages:
    20,668
    Likes Received:
    548
    Location:
    WA USA (Z8)
    The diseased one is an evergreen azalea.
     
  8. joclyn

    joclyn Rising Contributor

    Messages:
    2,707
    Likes Received:
    1
    Location:
    philly, pa, usa 6b

    and...

    azalea are in the rhododendron family...


    besides there being some kind of mold issue, it might just have reached the end of it's life.

    we had/have the same plants at the house i grew up in. out of a half dozen bushes there are only two left now. nothing was changed over the years - my parents never did anything other than maintain whatever bushes were there and my sis, who lives in the house now, hasn't done anything other than that either. no changes to drainage from the down spouts, nothing new planted, nothing dug up, etc. in the past ten years there was a similar type of die-off on the others and as they started to go, my sis just took them out (instead of trying to do something to help them).

    the house was built right after world war II, so they're more than 50 years old.

    it could be that whatever work you needed to do that was near the bush just caused it do this die-off a bit sooner than it would have otherwise (in other words, stressed it more than it could handle at it's age).
     
  9. eric_r

    eric_r Active Member 10 Years

    Messages:
    60
    Likes Received:
    1
    Location:
    Vancouver
    That certainly seems possible.

    Thank-you, everyone, for your helpful replies.
     
  10. joclyn

    joclyn Rising Contributor

    Messages:
    2,707
    Likes Received:
    1
    Location:
    philly, pa, usa 6b
    was thinking about this.

    obviously, you need to take off the parts that are definitely done. maybe do a strong all-over pruning and give it a good feeding?

    since it's so long established, it's obviously got a good root system. so, feeding the roots and giving it less foliage to have to deal with may be what it needs to bounce back from whatever damage was done during the work in the area.

    it's worth a shot, anyhoo.
     
  11. eric_r

    eric_r Active Member 10 Years

    Messages:
    60
    Likes Received:
    1
    Location:
    Vancouver
    Yes, I think it's worth trying. I'm still not completely convinced that it was the excavation done several years ago that is causing the problem.

    The plant still has over a dozen "branches" averaging 3cm in diameter coming from ground level, of which I only seem to need to cut off two at this point. (I cut a few others off last fall.) So it may still survive and come back.
     
  12. Ron B

    Ron B Paragon of Plants 10 Years

    Messages:
    20,668
    Likes Received:
    548
    Location:
    WA USA (Z8)
    Rhododendrons and azaleas belong to the heath family. Specimens of either should have the potential to live hundreds of years.
     
  13. Olafhenny

    Olafhenny Active Member 10 Years

    Messages:
    178
    Likes Received:
    0
    Location:
    Penticton
    and:
    The picture looks very much like one of my rhododendrons, the Rhododendron PJM HW Sargent. it is rather small leaved and seems t straddle the gap between rhododendron and azaleas. [Sorry my search on the net could not come up with any picture(s)]
    I had some problems with it, which hardly relate to those of eric_r or Liz. I had originally two, which responded well after the first winter, but after the second, one died and the other had sickly wilted leaves and flower buds. I assumed, that the problem had been a late start of the irrigation and made sure, that the next year I watered it by hand earlier, - with very limited success.

    It was only last December, that our local gardening guru recommended in his weekly column a thorough watering directly before freeze-up, because broadleaved evergreens transpire even during the cold winter months, using up the available water in the root zone.. And because we had a warm spell at the time, which temporarily eliminated the ground frost, I watered all my rhododendron profusely. So far it seemed to have worked. The sergeant is showing healthy buds, though the plant is still denuded of all leaves, but last years growth. I have at this time no idea, if that is normal for the species or just because of past stress.

    Now I cannot imagine, that this will help Eric, because Vancouver is neither as dry nor quite as cold for as long as Penticton, but I did come up with this site, addressing all kinds of problems with rhododendrons: http://www.rhodyman.net/rhodyho.html#anchor291256

    As for Liz, I don't know, how rhododendron behave in your climes. If they have a dormant period, watering during that period may help strengthen your plants???
     
  14. Chris Klapwijk

    Chris Klapwijk Active Member 10 Years

    Messages:
    271
    Likes Received:
    4
    Location:
    Black Ceek, B.C., Canada
    Olafhenny,

    Rhododendron PJM HW Sargent does not exist. There is the R. 'PJM' group, an interspecific cross of R. carolinianum and R. dauricum sempervirens and then there is R. 'H. W. Sargent', a R. catawbiense hybrid, which received a RHS First Class Certificate in 1865.
     
  15. Ron B

    Ron B Paragon of Plants 10 Years

    Messages:
    20,668
    Likes Received:
    548
    Location:
    WA USA (Z8)
    Plantings of 'PJM' often gradually die out in this area, it seems to be even more prone to root rot than usual. Or, there are just so many of them planted that there is more opportunity to see them consigned to unsuitable sites - heath family plants generally must have excellent drainage, as well as a cool root run. Plantings of heaths and heathers often show the same pattern, most of them dwarfed and sometimes dying out, with perhaps a few of them in the same grouping persisting and growing significantly larger. (In addition to being vulnerable to soil compaction they are also apt to break if stepped on directly, people cutting through commercial plantings soon create gaps in plantings of heath family shrubs).
     
  16. eric_r

    eric_r Active Member 10 Years

    Messages:
    60
    Likes Received:
    1
    Location:
    Vancouver
    I notice that "PJM" stands for "Peter J. Mezitt." Does that mean that two young specimens I have of Olga Mezitt (which are so far doing very well) are destined for possible trouble in the future?
     
  17. Olafhenny

    Olafhenny Active Member 10 Years

    Messages:
    178
    Likes Received:
    0
    Location:
    Penticton
    Hi Chris:
    As a relative novice in gardening (I am back at it for 5 years after 20 years of city life), I make it a point to keep all the labels on my plants, so I know what they are and which to get more of and which did not work out. Therefore I can still copy what is on the label that the plant came with.

    PS: To state, that something does not exist is always risky, because a non-existence is almost impossible to prove. :)
     

    Attached Files:

  18. Ron B

    Ron B Paragon of Plants 10 Years

    Messages:
    20,668
    Likes Received:
    548
    Location:
    WA USA (Z8)
    The answer is that the label is incorrect.
     
  19. Olafhenny

    Olafhenny Active Member 10 Years

    Messages:
    178
    Likes Received:
    0
    Location:
    Penticton
    Fill me in: How can you be so sure about that? Is there a comprehensive registry of plant species? What precludes this particular species from existing?
     
  20. Chris Klapwijk

    Chris Klapwijk Active Member 10 Years

    Messages:
    271
    Likes Received:
    4
    Location:
    Black Ceek, B.C., Canada
    Olafhenny,

    for a list of about 1,000 rhododendron species, see this page; however, your plant is a hybrid, not a species. There are at least 28,000 rhododendron hybrids registered with the RHS.
     
  21. Olafhenny

    Olafhenny Active Member 10 Years

    Messages:
    178
    Likes Received:
    0
    Location:
    Penticton
    Thank you Chris, this Post was very informative and appreciated and explained to me why your assertion was valid. It also explained, why I was unable to find a picture of "PGM H.W. Sargeant" ;)

    I do, as a rule not just want to know, "that it is so", but also "why it is so", and your last post explained that. So again: Thanks
     
  22. Chris Klapwijk

    Chris Klapwijk Active Member 10 Years

    Messages:
    271
    Likes Received:
    4
    Location:
    Black Ceek, B.C., Canada
    Olafhenny, you're welcome.

    eric_r, there is some doubt as to the exact parentage of R. 'Olga Mezitt'. The official RHS registration lists the parentage as R. minus Carolinianum Group x R. minus var. minus. Noted rhododendron expert Ken Cox reports its parentage as possibly R. minus 'Compacta' x R. mucronulatum.

    Either way, R. 'Olga Mezitt' is a different hybrid, so there is no reason to assume it will suffer to the same fate as R. 'PJM', if that is what it is, but so far the plant has not been identified.
     
  23. Liz

    Liz Well-Known Member 10 Years

    Messages:
    1,526
    Likes Received:
    2
    Location:
    Victoria Australia [cool temperate]
    "As for Liz, I don't know, how rhododendron behave in your climes. If they have a dormant period, watering during that period may help strengthen your plants???"

    Normally we are perfect for azaleas rhodos etc. Deep red acid volcanic soil, elevation above sea level and good normal rainfall or the ability to water regularly. The problem now is, not allowed to water except for once a week for an hour. So many of my plants have had to fend for themselves. We have had very good fall of rain in the last 24 hrs and every thing is looking a lot happier. There is more to come so I will scrape some of the mulching back to let water penetrate and we will hopefully survive another year. I have noticed some of the plants under stress have shut a branch off which is totaly dead but the rest is fine. The weather has been so dry there are many dead natives as well.

    Liz
     
  24. eric_r

    eric_r Active Member 10 Years

    Messages:
    60
    Likes Received:
    1
    Location:
    Vancouver
    Thanks, Chris, for clarifying that matter.
     

Share This Page