Rhody Malady

KeppyJune 30, 2013

I have a big tree rhody which I've been tending for 30+ years. Trimming out deadwood from inside the canopy I notice orange bands/girdles going around the trunks, some continuous, some broken, some single and some with several together one above the other. They are swollen slightly and have broken the bark. I've take a gouge and carefully cut into some of these lines. I go through the orange crust which has displaced the bark and below that I find tissue which is a blue red. Carve a little deeper and I find white tissue with a thread-fine dark line running with the girdling. The tree seems healthy, now with good leaf growth after normal flowering.
I've take photos around (WA) and no one locally is familiar with this girdling pattern. It sounds like a boring larvae except that this does not seem to penetrate the wood of the tree and it clearly goes radially around branches. Shown the pictures, a local nursery suggested I carve to the white tissue, apply and dilution of clorox and then copper fungicide. But they seemed uncertain of the cause and that approach pretty radical without knowing. Besides, it's not clear to me that the plant is being hurt. I am new to this forum, and would be grateful for your help!

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jean001a(Portland OR 7b)

Please post images

    Bookmark   July 1, 2013 at 1:41AM
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Keppy

Jean, thanks for your response. I haven' had great success posting photos to forums, but I'll try. I have plenty! Perhaps there is a procedure given here for posting them...

    Bookmark   July 1, 2013 at 10:05PM
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rhodyman(SE PA, USDA Z6)

I sounds like a harmless lichen growth. Removing the bark under the lichen growth would definitely kill the end of the branch.

Lichens are a fungi/algae association which use the bark as a growth site, not a feeding site. They can be controlled chemically, if desired, for appearance. Although often associated with spindly, unthrifty plants, lichens cause no damage to the plant.

Provide optimal care to the rhododendron, as lichens are often a sign of plants in need of cultural attention.

On the other hand it could be the alga Trentepohlia which forms a vivid orange powdery deposit on tree trunks and branches. It is commonly found with lichens.

Here is a link that might be useful: How to grow rhododendrons and azaleas

    Bookmark   July 5, 2013 at 10:46AM
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