Could this be root rot on my rhododendron?

lizzie_nhMarch 22, 2012


I know no one will be able to give me a definitive answer, but here goes... I'm wondering in particular whether a certain problem is likely to occur so early in the season.

I planted two rhododendrons (roseum elegans) in May 2009, so this will be their 4th summer. They are now maybe 5' or 6' by 5' or 6', and have thrived, planted on the north side of the house, side by side (but well-spaced), sheltered, and in well-drained acidic soil. Last year was (I think) their first year to shed leaves, which is apparently normal in the third year. I don't recall noticing any particular area losing leaves, or the plants looking unhealthy... I think they lost lower leaves as they grew leaves further along the stems, and this occurred in both plants, and over the whole plant. This past fall they looked lush and healthy.

Now, here in central New Hampshire, like most of the country, we had a very mild winter. Temps were higher than normal, but more notable was the lack of snow. We still had plenty of very cold days... just almost no snow. On those cold days, I noticed the typical tight curling of the rhododendron leaves, and while during the winter I didn't inspect carefully, from a distance, they all seemed to unfurl again when the temps went up.

In the last week or so, though, I have noticed that on one of my plants, there is a large section in which the leaves are still curled. It looks like roughly 1/4 of the plant may be dying.

I did an internet search and learned about phytophthora dieback and root rot. Outwardly, this is what appears to be the problem. But, I read that if you scraped the bark on the stem close to the soil line, you would see dark brown or red... but I see normal healthy-looking greenish-yellow tissue.

So here is my question for anyone here... if you have experience/knowledge of this condition, do you think that it would occur this early in the spring? The ground is not particularly wet, especially considering the lack of melting snow. We have had very warm (freakishly warm) temps (80+) the last 5 days, but in general, I don't think the soil is extremely warm yet. There's perfectly good drainage in this area and the other plant looks unaffected.

Does it sound more like it might be dessication from a cold winter in which the plant was not covered with snow? I'm hoping that at worst I can lop off the dying part and not have the problem spread. The plant will be lopsided, but better than to lose the whole thing... it would ruin the appearance of that side of the house and it's just finally growing into something which looks like a mature plant.

Thanks for any help... these are my favorite plants (some of the first I added when landscaping my house) and it would be quite devastating to lose one. Sigh.

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mad_gallica(zone 5 - eastern New York)

Check for borer holes on the affected stem.

    Bookmark   March 22, 2012 at 2:37PM
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Here's a photo:

    Bookmark   March 22, 2012 at 2:40PM
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Thanks - I'm not sure I know what to look for, but I did a google image search and I don't see anything which resembles those images of borer holes. And would those occur so early in the season? I know we've had unseasonably warm temps, but it is still March in New Hampshire. A week ago we still had a little snow left on the ground (although that was basically ALL the snow we'd had all season... we had about 3 weeks with any snow on the ground.)

    Bookmark   March 22, 2012 at 2:48PM
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The damage (whatever it is) could have happened earlier. It's not like such a big plant normally die right away. Roseum Elegans is one of the hardest varieties as far as the frost is concerned. Only very prolonged drought combined with frost could possibly damage it(so it is advisable to water also in the winter if necessary, and in late autumn). So you probably have some sort of fungus at play. As far as I know Roseum Elegans can be pruned really hard, and it is usually on its own roots. This way you can also make it branch better from the bottom. Good luck!

Also check if there is bark around the stem just beneath the surface of the soil. The larvae of Curculionidae-beetles could have made a damage there.

    Bookmark   March 22, 2012 at 3:33PM
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morz8(Washington Coast Z8b)

Curculionidae-beetles - not an issue of importance with rhododendrons in New Hampshire that I'm aware of. If there were weevils, you would be seeing an amount of notching on the leaves caused by the adults feeding long before larvae would cause significant root damage....I think I can see some possible weevil damage in your photo but minor and what I would call cosmetic.

Were the plants watered and healthy going into winter? Sometimes rhododendrons will respond to drought by losing branches or sections of the shrub - almost like they are sacrificing portions to keep the remaining supplied...

Bark split is another possibility if exposed to a hard Fall or early winter freeze that came on suddenly.

You might want to take your questions/photo to the Azalea and Rhododendron forum where you could bring it to the attention of experienced growers in your climate - I don't think they would be looking to help on the perennial forum.

    Bookmark   March 22, 2012 at 8:30PM
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ken_adrian Adrian MI cold Z5

thats how mine look all winter long.. simply looking tired and droopy ..

have you had the warm spell yet.. they usually perk right up ...

if its just that branch.. snip it off, way back at the trunk.. or to proper leaves .... look at it.. and throw it away ...

and then spend the rest of the summer watching it fill the hole back in ...

there are many mysteries that are never solved in the garden ... for all we know.. some drunken frat boy fell into the plant at 2am one night .... and broke the branch .. frankly.. thats as plausible as any other suggestion ...

if.. upon inspection.. you find anything out of the ordinary.. get a better pic.. but i bet you might find it broken down by the trunk ...

but i wouldnt go worrying about root rots.. and chemical interventions.. etc ...


ps: do you live near a frat??? ... lol

    Bookmark   March 22, 2012 at 8:57PM
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Thanks everyone. No, no frats in the vicinity. :-) I checked and the branch isn't broken (unfortunately.)

Yes, we've had a major freakish warm spell with the last 5 days being over 80 degrees, and the rest of the plant, and the other plant, has perked up and looks lush and healthy.

I do have notching on some of the leaves, but I have considered it "cosmetic"... I wonder if it is more serious than I thought.

I watered until late autumn and then after that it didn't make sense to water since (I assume) the plant was dormant, and the ground was frozen solid.

Today it looks like those branches are definitely dead... dried up... while the ones with healthy leaves are a greenish red and more flexible. I had wanted to wait to prune until I see new shoots (hoping for some miracle, that I will get new growth on the branches with the curled leaves) but now I think I will go ahead and prune them. I'm hoping this is not a problem which will spread.

    Bookmark   March 23, 2012 at 9:35AM
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ken_adrian Adrian MI cold Z5

and the rest of the plant, and the other plant, has perked up and looks lush and healthy.

===>> so its doubtful.. that a root rot.. would affect half a plant ...

I'm hoping this is not a problem which will spread.

===>>> and to avoid that worry.. CUT IT OUT ... we dont wait to see if it will sprout and recover.. just in case there is something there that is bad ...

what is your avoidance of simple pruning all about??? just do it ...

you have spent more time turning on the computer.. logging on.. repeatedly.. posting.. replying.. etc .. than the total amount of time. it would have taken me to simply walk to the garage and get the pruners.. and cut it out ..

its so simple.. and reduces worry to zilch ..

i dont get peeps avoidance of pruning.. its not a child.. cut it off ...

but if it makes you happy.. to leave it.. and worry.. and hope .. all the power to ya .. go for it ...


    Bookmark   March 23, 2012 at 12:18PM
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Lizzie, with severe infestation of weevil larvae, some plants(especially younger) can actually die. Here in Denmark we can fight the weevil larvae with a biological weapon. We can buy some nematodes and apply them while watering. It is also advisable to collect the adult beetles at night time with a flashlight, before they lay eggs.

    Bookmark   March 24, 2012 at 5:49AM
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:-) Ken

By the time you posted your pruning rant, I had already pruned it out! I wasn't avoiding doing so, but rather wanted to understand it first. From what I could tell online, root rot could show up on certain areas of the plant and then eventually spread to the whole plant. The same thing could also happen with other diseases/pests.

But, as it turns out, I think it may merely be drought. While our winter was exceptionally mild, we still had plenty of below freezing temps, without the usual snow cover, and I live in an area which sees high winds. I read the plant will become dessicated but since the ground is frozen, it won't be able to draw water. In such a situation it is common for the plant to sacrifice one branch to save the rest of the plant. Upon further inspection, this was all coming from one main branch. I inspected for any sign of bugs, and there were none on the outside, or under the bark when I scraped it back. I also didn't see any of the darkening of the wood tissue near the soil line which would suggest root rot.

My only fear now is that I pruned so close to the ground that it will not send out shoots in that area. But better a lopsided plant than a totally dead plant.

wieslaw - thanks for the advice about applying the nematodes. I will try that. I don't think that problem is too severe, but I would like to keep it from getting too severe.

My first worry now always seems to be "fungus" because we've had some big problems. A few years back we laid some new sod and there was SOMETHING in it... either a fungus or a grub (although we saw no grubs/bugs) and one roll started dying at a corner and it spread throughout the entire lawn (close to an acre) very rapidly. We lost everything. Then this past fall we were growing grass from seed in a relatively small area. I laid down bags of top soil and seeded... it came up quickly, lush and green. It then rapidly was overtaken by some sort of fungus and all died (but the death did not spread beyond the boundaries of the new soil, so it was something in the soil.)

    Bookmark   March 27, 2012 at 11:10AM
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Several of my rhododendrons look a lot like the photo. I'm just leaving the damage as is for now. It was such a weird winter, with no snow and wild temperature fluctuations, that unless proven otherwise I am assuming it is weather damage. Unless the whole branch is dead, they will send out new leaves, either from existing buds or from dormant buds that will emerge from the stems. I have this type of damage on three or four varieties of rhodies in two different areas about a half mile apart. Usually my rhodies are disease and insect free, so I'll only remove the branches if they still look bad in June.

    Bookmark   March 28, 2012 at 9:29PM
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