Rhododendrons: Phytophthora or ??

Discussion in 'Ericaceae (rhododendrons, arbutus, etc.)' started by KarinL, Mar 3, 2008.

  1. KarinL

    KarinL Well-Known Member 10 Years

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    This Rhododendron is not looking so good - gradual leaf death happening from the bottom up. Doesn't really look like normal annual leaf loss to me, although the buds look promising. And when I cut off a few scraggly stems, they were green inside so don't seem to be dead.

    I haven't done anything to this plant except bring it home last fall from the nursery, so my legendary plant "care" is not to blame. But although the plant is a good size for its two gal container, the roots did not extend beyond the top half when I pulled it out of the pot yesterday.

    I'm wondering whether these symptoms are suggestive enough of phytophthora that I should isolate the plant and sterilize my tools!

    By the way it is a purple-leaved variety that is just greening up after being purple in winter, so the top-most leaves do look healthy, not browning.
     

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  2. chimera

    chimera Well-Known Member 10 Years

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    Maybe damage from cold, wind, and/or lack of water, drying out over winter ? Wondering how the bark and crown look at ground level, in case of girdling by weevils or crown gall. Assuming the roots looked healthy and no weevil grubs in the soil mix. Don't know if it would be a phytopthora problem, but you could repot it in new soil mix after washing the present soil mix off the roots, and see how it does for a while.
     
  3. Ron B

    Ron B Paragon of Plants 10 Years

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    Looks like winter burn. If it sat out on top of the ground all winter probably the roots froze back, anything happening to the roots will definitely affect the top - the roots call the shots.
     
  4. growest

    growest Active Member 10 Years

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    Hi Karin--no answers but just a comment about roots only in the top half of a #2 pot.

    I've seen so many rhodo's for sale in rootbound containers, I'm just shocked that this plant was rooting that way. It seems a universal rule here to grow rhodo's in small containers, I assume because they will continue to grow in such conditions and thereby save on repotting costs. The downside comes when planting out, they take longer to establish in the landscape...if they ever do (I've seen them years later struggling still with those rootballs still well defined in the planting beds, yikes!).

    Hope you find the answer for this one...I do agree that the roots hold the key.
     
  5. Ron B

    Ron B Paragon of Plants 10 Years

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    The roots are often in the top half because these plants require a higher-than-usual degree of soil aeration. Rhododendrons growing in the ground also prove to have a sodlike superficial mat of roots when dug out of less-aerated soils. Sometimes they are discovered to be growing in the mulch only, except for the deeper, original soil ball below the crown.

    Pots have perched water tables, water draining through the soil column inside the container backs up when it encounters the bottom of the container. When field capacity (saturation) is reached, then it pushes its way through and rushes out the drainage openings. Rhododendrons potted in older mixture that has partly decomposed or never was coarse and aerated enough to prevent it will not root into this repeatedly sodden lower half.
     
  6. KarinL

    KarinL Well-Known Member 10 Years

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    That does pretty much describe the lower part of the planting medium - compact and soggy. Must have been bark-based at some point, but in the container too long, I suppose. Which is perhaps a warning to me not to buy plants at season's end, which I all too often do. Or at least if I do, not to leave them potted even longer.

    Nice to hear that something other than Phytophthora could be at work here; specifically I hadn't thought of weevils, which is silly of me since I definitely have them here, and I will give the roots a good wash out and replant with better aeration. To some extent I had done this, but was reluctant to risk too much disturbance and spreading of possibly contaminated soil.

    Mind you, even if the plant has phytophthora, it seems to spread so easily (through water movement!!!) that it will likely have done so already and it is delusional of me to think I can protect the rest of the yard. So I may as well give the plant a good rescue attempt.

    Combined with the healthy buds on the plant, your collective comments have given me hope - thank you!
     
  7. Ron B

    Ron B Paragon of Plants 10 Years

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    Bargains often aren't. A plant can even be a "nice" green and have a nitrogen deficiency at work. Yellow-leaved ones are definitely past it. For whatever reason, black vine weevil infestations of container stock seem to be fairly consistently associated with overly damp conditions at the root. The ones in a block of the same stock that are found to be full of grubs when dumped out or bare-rooted will also be the ones living in muck. Maybe it's simply a factor of time, the same interval that allows an infestation to have developed will also have been long enough for the potting medium to have aged and decomposed.
     
  8. chimera

    chimera Well-Known Member 10 Years

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    Karin, when you're replanting, the roots can be teased out, or if tightly potbound it seems to help to score the outside of the root mass on the bottom and about 4 times or so vertically around the edges to encourage new root growth into surrounding soil. Your likely already aware of this, but it may help other readers.
     
  9. Ron B

    Ron B Paragon of Plants 10 Years

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    I wouldn't maul a rhododendron, their roots are like sods. I would dispose of this specimen, as if it has something more going on that frost damage it could spread. It could even have sudden oak death! Definitely likely to dawdle, perhaps for years, whatever its problems are.

    I've grown weary of wasting my time on sad plants, that malinger or die after planting out.
     
  10. KarinL

    KarinL Well-Known Member 10 Years

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    Well, I went digging into the roots this afternoon. Found no weevils, but even fewer roots than I had previously realized. There were really only fine roots on the surface of the pot and the top third of the sides and still more really soggy planting medium. But in the middle the main roots felt healthy and were not girdling or otherwise deformed.

    I usually do score the root ball but there was no root ball at all! I teased out what I could and put what remains into a better aerated situation; will watch with interest to see what happens (wonder if roots can recover just as it starts to bloom). I actually get kind of a kick out of the rescue effort so don't mind - though obviously I will regret it if it infects the garden with something. But the root teasing really, really looked like a simple rot problem.

    Thanks again.
     
  11. Chuck White

    Chuck White Active Member

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    The wall behind the plant has enough green 'moss' growing to make me think that the pot is sitting in a very wet spot. The root system could be compromised. Perhaps a check during a rainy day.???
     
  12. KarinL

    KarinL Well-Known Member 10 Years

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    Actually a good call, Chuck, but that is not where the pot was sitting but the garage wall where I've put my potting table (such as it is). I think it was wet everywhere in the yard, and yes, the root system was compromised by having rotted mostly away. Sorry, I should have posted photos of it! I've planted it, and the plant seems to be stable - leaf loss has slowed down.
     
  13. KarinL

    KarinL Well-Known Member 10 Years

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    I thought I would post some updated photos of this plant. I took these yesterday when the dying flowers were soggy with rain so it might not be its best day, but as you can see it has experienced selective die-back of quite a few stems while others have thrived and are even sprouting new growth. Even one of the apparently dead stems is sprouting new growth (that photo not in focus, so haven't posted it).

    I find this interesting apropos a discussion about trimming roots when transplanting (pro-con) that took place recently on another thread. Obviously, after the experience of root rot, some of the top growth no longer has the feeder roots it requires, and has died off correspondingly. But when I was planting it, I could not have predicted which part of the top growth would survive or which would die. If I had cut out what I thought was right from the top, I might have cut off precisely that part that has in fact survived. As you can see from the base, one of the main stems has to go, and I was in fact humming and hawing over which one to cut... but decided to wait and let the plant have some say in the decision. It definitely had an opinion!
     

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