Help for Rhododendron occidentale with leaf wilt.

Discussion in 'Pacific Northwest Native Plants' started by GregR, Mar 16, 2017.

  1. GregR

    GregR New Member

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    I have little plant experience, but I got lucky with this one plant.

    I have a 6'-7' /8" base 50 year old white Rhododendron Occidentale which has leaf wilt. It's been on the SE side of my house for forty years. It is shaded from the afternoon sun. The leaves have always been an olive green color not the darker green I see on many Rhodies. The leaves of the natural Rhodies I've seen in the sierras are darker than mine. I always fertilized it every year or so.

    About 6 years ago, it got so big, I cut it back about 12" at the top. It seemed to like this trimming and sprang back with more shoots and flowers. Last year, after flowering, I cut it back again about 12". This winter I noticed it had unusually wilted leaves all over. I hadn't fertilized it for a couple of years. The are a few holes in many leaves. So I fertilized it well and considered digging it up and replacing the soil for better drainage. Not to be rash, I waited.

    For the past ten years there has been a fast growing evergreen volunteer directly in it's limited sun exposure. I wasn't worried about that since the rhodie grew it's first 40 years in the shade of 4 junipers that died of oak root rot and beetles 20 years ago. Now I’m worried about every possible thing. We had double the rain as normal.

    Today after reading another slew of articles about root rot and too much mosture, I decided to trim back any dead branches. It’s leaves looked a little less wilted today. We’ve had a few days without rain. I was thinking of digging a 3” trench around the drip line and out to the driveway for drainage. I also thought of taking plywood or plastic and making a low shed around the base to shed more water away from the roots…

    What do you think,

    greg
     
  2. Keke

    Keke Active Member

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    In my experience, rhodos don't require a lot of fertilizer. Over-fertilizing could burn the roots, depending on what kind of product you use -- remember, rhodos have roots very close to the surface of the soil, and those roots extend out further than the dripline. I have always spread a scant amount of granulated rhodo-specific fertilizer after bloom has finished, and that's it for the year. Because the roots extend so far, I would also caution you not to dig that trench!

    I suggest looking at a couple of other possibilities before you decide what to do. First, what do those holes in the leaves look like? Could you have vine weevils? If you do, that can greatly affect the roots as the weevil larvae feed on rhodo roots after hatching and before they climb up the trunk to lay their eggs. Luckily these pests can be controlled using non-chemical methods. See this for more info: Root Weevils: Troublesome Rhododendron Pests

    Second, make sure the wilting you saw wasn't just the rhodo's usual response to cold. We had a much colder winter than normal, and rhodos wilt to keep themselves from losing moisture from their leaves. Some tender rhodos wilt at a higher temperature than usual. Now that we are getting warmer weather you won't see the wilting.

    Third, have you cultivated, top-dressed or mulched around that rhodo? If you haven't, don't. If you have, remove the mulch/top dressing or stop cultivating. Because rhodos have surface roots it's very easy to damage them or smother them, which will cause root rot.

    I hope these ideas help. Feel free to ask any more questions or post pictures of the "patient" so we can better suggest what to do.
    Cheers
    Keke
     
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  3. GregR

    GregR New Member

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    I when to my local nursery and they mentioned that the wilting look was probably the extreme rain we've had this year. We've had as big rain years before and colder years with frost and actual freezing too, without the wilt look. Average temps are from 45-80˚F. My Rhodie is a few feet from my house on about a 1% slope. Two years ago I played bricks down for a path on the down hill side. It was outside the drip line and I didn't dig them into the ground more than about one inch in some places. They must have acted as a dam for the water flow and as an impediment to the drying of the earth. Since the leaves looked less wilted after days of sun, I removed the bricks nearest the drip line for drying, removed some for water egress and built a shed roof on the up hill half of the ground under the Rhodie to shed rain to the side driveway. Today the leaves looked like they perked up a bit or I'm just more hopeful.

    This pix #2 is the worst looking leaf, others don't have such a large brown area or as big a hole. The back of the leaves have tiny brown dots and the edges have fine short hairs that may just be part of the plant. Is that olive green color normal for this variety? Would pinching off the buds help the plant conserve energy to heal? How far do the roots go past the drip line?
    Rhodie Leaf back.JPG IMG_0478.JPG
     
  4. Keke

    Keke Active Member

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    I wouldn't worry about the colour. I have rhodos which are very similar in colour to yours and they're fine. I have others which are dark green and others which have a bluish colour. Dots and hairs are often features of rhodo leaf undersides so you're fine there too. The holes don't look like weevils, thank goodness.

    The roots extend quite a bit further than the dripline, and most of the actively growing rootlets are no more than an inch or two below the soil surface. When speaking to a rhodo breeder some years ago he said open-grown rhodos could easily be moved by cutting the soil a foot past the dripline all the way around and scooping the plant out by taking only the top 3"-6" of soil. He said that's one reason why potted rhodos don't always transplant well. They actually have very few roots.

    I'd probably just leave the poor thing alone and let it come back by itself. I'd probably let it bloom, because pinching the buds could introduce pathogens or pests when it's weaker than usual. Helping its drainage is a good idea but don't go overboard. Once we get into warmer weather rhodos prefer regular water, again because the roots are so close to the surface, so they dry out fast. I bet it's had a rough few years with the drought, and then all of sudden it had too much water this past winter. Interestingly, the old junipers you used to have might have helped it in times of too much water in the past because they love water, and may have siphoned off any overage.
    Cheers
    Keke
     
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  5. GregR

    GregR New Member

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    Thank for all the help Keke.

    I noticed you're from Vancouver and thought "that's far away." I just realized that I'm the one far away. I read UBC as UCB, which is about two miles from me.
     
    Last edited by a moderator: Mar 17, 2017
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