Rhododendrons: Help - Really Sick Rhododendron!

Discussion in 'Ericaceae (rhododendrons, arbutus, etc.)' started by Unregistered, Dec 12, 2005.

  1. I do hope you guys will be able to help me on this one. I am quite new to gardening and could really do with some advice as I think without it I am going to lose a beautiful rhododendron which we bought and planted in May. When we bought him he was green and perky - he didn't flower but at the time we suspected that it was due to the trauma of being moved. We bought three rhododendrons at the time and they all seem to be in fine health. It wasn't until a couple of months ago that this one started to drop his leaves. I don't remember them being particularly curled but the process did seem to happen quite quickly. He has been fighting the good fight ever since and I am amazed that he's still with me now (admittedly only just).

    The soil we have here is heavy clay, so, to try and compensate for this my partner and I dug out a large amount of it and replaced it with three big sacks of ericaceous compost. The summer was dry and I was too naive to water as much as I should have done (I have since realised how neglectful I have been - I am a bad mother). I suspect too that the sprinkler which we planted by his roots is probably too close and could have caused some damage. I am also wondering now if we have planted him too deep.

    It is hard to describe his symptoms. He has lost most of his leaves and some of the twigs have died. Some of the new leaves have gone brown and come away easily. I have checked for signs of bugs (at night with a torch as well as in daylight) and can't see any signs. He has been planted in the shade of the house which could of course upset him but one of his friends is on the patio in the same amount of shade and is doing very well indeed (although this is a different variety).

    My new concern now is that the azalea, which is planted next to him, has, this week, turned yellow and started to shed some of its leaves. Admittedly this week we have had a heavy frost but I am really scared that this is a fungal infection that will spread!

    Please help - a sorely abused plant is relying on your advice!
     
    Last edited by a moderator: Jan 21, 2021
  2. Ron B

    Ron B Paragon of Plants 10 Years

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    Search these terms:

    Powdery Mildew of Rhododendron
    Rhododendron Root Rot

    Next time plant in mounds or berms of sandy soil on top of the clay, instead of planting in pits of planting mix dug out of the clay (this can work if you make the excavated area very large--larger than most home gardeners would think of doing. Otherwise, if the water table is high enough you have merely created a sump).
     
  3. Hi Ron

    Thanks for the advice. We did take out three wheelbarrows full of clay but I get the point. I've checked out your leads but it doesn't seem to match up with powdery mildew and I'm still not sure whether or not it is root rot - I've spent several weekends reading about it since but could do with something more to go on...
     
  4. oscar

    oscar Active Member

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    When planting in clay soil make sure you dont smooth the sides of the hole with the spade, it will just make an almost water tight sump.
    I'm assuming you didnt do this and the problem lies else where, did the edges of the leaves brown first then fall off.....was the plant dry when you planted it? Did you add fertiliser to the soil when you planted it?
    The azalea might be a deciduous one.
     
  5. Erica

    Erica Active Member

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    Oscar- I'm not the OP, but what do you mean about the deciduous azalea? How do you know if you have one? I thought all of them were evergreen.
     
  6. oscar

    oscar Active Member

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    Hi Erica

    Here's a guide to the Different sorts of Rhododendrons and Azaleas

    Evergreen Rhododendrons, Often known as "hardy hybrids", derived from
    R. catawbiense, R. Ponticum and R. caucasicum crosses. Evergreen Rhododendrons vary in habit from small-cushion forming shrubs to tree Rhododendrons.

    Vireya rhododendrons from S.E.Asia are evergreen and tender. they flower throughout the year and are best grown as conservatory plants.

    Evergreen and deciduous azaleas, belonging to the botanical section Azalea within the genus Rhododendron, Azalea hybrids may further be divided into the following sub groups:
    Deciduous hybrid azaleas, Belgian raised, fully hardy, resulting from crosses between American azalea species and R. luteum. Usually scented flowers in early summer.
    Knap Hill-Exbury hybrids English hybrid azaleas, with complex origins(American azalea species crosses with R. molle. scented or unscented in a range of bright colours in mid-late spring.
    Mollis hybrids Dutch and Belgian origins, and are a result of crossing R. molle subsp. japonicum and Rhododendron molle. Unscented flowers, before the leaves in late spring.

    There are dozens of other smaller groups of hybrids, raised by crossing all sorts of rhododendrons. When buying Azaleas and rhododendrons always buy from a reputable source, and always make sure it has a label clearly stating what type it is.

    The quickest way to tell if a plant is evergreen or deciduous is to touch the leaves, papery leaves, usually deciduous, waxy, plastic feel and its probably evergreen.
     
  7. Erica

    Erica Active Member

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    Thanks very much, Oscar!
     
  8. Gordo

    Gordo Active Member 10 Years

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    I would agree with Ron that you might want to try planting on mounds or berms in the future - rhodys seem to like this, provided they get sufficient water. Also, try checking out some the wonderful arboretums and gardens in the area which faeture rhododendrons, so you can see the incredible variety we are able to grow here. Often you can get recommendations there for exceptional performers in the PNW. Here's one:http://www.meerkerkgardens.org/
     
  9. GRSJr

    GRSJr Active Member 10 Years

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    Ron has pointed out the probable problem. With heavy clay soil, raised planting is essential. Phytophthora Root Rot is the most probable problem and fits your description of the symptoms.

    S. Krebs & M. Wilson, "Resistance to Phytophthora Root Rot in Contemporary Rhododendron Cultivars", J. HortScience 37:790-792.

    Describe tests that determined cultivars that are resistant to Phytophthora in case you have to replace the dead ones.

    Treatment with Subdue is recommended, but in my experience, it simply slows the process some. We too have heavy clay and our plantings are in mounds above grade, but Phytophthora strikes anyway.

    In desparation, I experimented with a new product called Messenger. It causes one of the genes in the plant to turn on it's immune system full force.

    To my amazement, even very sick plants recovered remarkably. I can't vouch that it will work on every cultivar, but it sure saved many of the ones I have.

    I also had the problem with Taxus brownii and it worked wonders there too.

    If I were you, I'd apply it to the Azelea immediately and then hit the Rhododendron. Drenching is NOT requires, simply spray until the leaves are wet.

    'Gomer Waterer' and 'Boule de Niege' were not saved by Messenger. 'Chionioides', another 'Boule de Niege' , 'Champagne', 'Scintellation', and the Taxus brownii all were. Other cultivars improved in health as well. All have continued to improve with an application of Messenger each spring.

    These have been my experiences, yours may differ.

    I would recommend lifting the sick Rhody so that it's root ball is above grade once it responds to Messenger. Likewise the Azalea.
     
    Last edited: Feb 6, 2006
  10. oscar

    oscar Active Member

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    Any news from the original poster, did the plants recover, or did they die.
     

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