Brown and spotted leaves on Rhododendron

extragalactic(6b)April 13, 2009

I have an established Rhododendron that is showing brown, dried, drooping leaves with black spots this Spring. Most of the plant is OK -- the diseased leaves appear on the ends of some branches, but not others.

It is planted in a little-bit acidic soil (near to a Hemlock tree), part shade (some afternoon Sun), appears well-drained, and is not regularly watered (well-established at least 10 years, I am guessing).

A neighbor's Rhododendron (located 50 feet away) is much more heavily impacted by what appears to be a similar affliction.

I've looked through some pages here and elsewhere (Penn State) but am unable to make a definitive diagnosis.

Any ideas what is wrong with these Rhododendrons?

Picture links: (1) diseased leaves (close-up); (2) neighbor's plant (note drainspout behind it!).

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mainegrower(Z5b ME)

Both plants show not so much disease as winter burn - combined effects of cold, wind and sun. The tightly curled brown leaves will not recover - the rest of the plants will. Rhododendrons are subject to many fungal infections which result in black spots. These diseases tend to be more unsightly than lethal.

    Bookmark   April 13, 2009 at 4:39PM
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Thanks, mainegrower, it's nice to hear that it is likely damage not disease.

What is the best action to take with these stems? Prune the stems down to the next set of healthy leaves / side-branch? Do it now or wait until after bloom in a month or so (when I would normally prune it)?

    Bookmark   April 13, 2009 at 4:46PM
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mainegrower(Z5b ME)

I'd wait until your normal pruning time. Most of the leaves in the photo of yours do not look too bad. You can cut back to the point where you see a green swelling of new growth or just let the browned leaves fall off naturally. The latter course results in naked stems which won't look great, but if you pinch out the growing point on lower branches to encourage bushiness, it will soon fill in.

The extremely curled leaves on the neighbor's plant may mean that the stems themselves are too damaged to recover. Cut these back to a growth point on live tissue - might as well be done now.

    Bookmark   April 14, 2009 at 4:20AM
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Thank you very much for the advice!

    Bookmark   April 14, 2009 at 12:14PM
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jean001(z8aPortland, OR)

Sorry to be a wet blanket. But your neighbor's bush is likely to have root rot.

Beyond that, the neighbor's droop is different than yours.

    Bookmark   April 19, 2009 at 1:45AM
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rhodyman(SE PA, USDA Z6)

You neighbors is probably not root rot. Root rot usually kills the entire plant. Drought damage kills individual branches as does borer damage. Those curled brown leaves are on dead branches. They will not come back.

Your damage looks more like winter damage on areas more exposed to sun and wind.

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

    Bookmark   April 19, 2009 at 6:01PM
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