rhody wilting: drought or rot?

georgiapeach1974March 9, 2010

Spring has finally sprung after a particularly long and hard winter here in NJ. I have begun inspecting my gardens and, sadly, I have discovered two rhododendrons I put in two years ago look terrible. I saved them from the deer but I think I'm going to lose them to something else now. About half of the leaves are turning an unattractive army green and curling up. I pruned a dying stem and cut it in a few places; where it was attached to the plant the stem was green throughout, but the higher up I trimmed, the more brown I found inside the stem. At the top there was really no green inside at all.

What I cannot tell from reading on the topic is if the plants have Phytophthora Root Rot or if they need water. We've only been above freezing during the day for about a week now, so it seems too cold for a fungus to do so much damage already. The soil around the base of the plants is moist (but not wet), so I am not sure that the wilt is being caused by drought either. And it seems unlikely the plant is lacking water since we've had significant snow melt in the last few weeks. Can anyone help me try to determine the cause here? Wilt caused by drought and wilt caused by rot just seem to manifest in such similar ways... I am going to try to post pictures to aid in dignosis if I can figure out how.

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I reposted this under image galleries with a picture...See the same topic from today.

    Bookmark   March 9, 2010 at 11:17AM
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mainegrower(Z5b ME)

I haven't been able to access the photo but neither fungus nor drought are at all likely - in fact, I would say that unless the damage was apparent before winter you can rule out both as causes. From your verbal description, I'd say the damage is the result of extreme dessication from sun, cold and wind. Wait a while to see if things improve. If they do not, prune back to live tissue. Don't be in a rush to do anything, though. It's entirely possible the roots are still frozen and cannot yet take up water.

    Bookmark   March 9, 2010 at 3:29PM
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Hi Georgia Peach,

You haven't had a drought problem in New Jersey this year, so your rhododendron isn't likely suffering from not having enough water in the soil.

We've often seen this kind of wilting problem here, and I'd guess your problem is very likely due to Photopthora, but less likely to be Phytophthora Cinnamoni (which comes from the roots) than another kind of Phytophthora wilt that comes from the leaves. It moves downward toward the roots as it spreads. If you let it get all the way to the roots, the entire plant will die.

It might be just the beginning of Phytophthora Cinnamoni, but probably isn't, not unless your soil has poor drainage.

As soon as you notice even a single stem wilting and are perhaps wondering whether it could possibly be root rot, but then see that the rest of the plant looks fine, cut out that stem with the wilting leaves all the way down to where it joins the next larger branch. If it's not totally green where you made the cut, then you'll need to do some more cutting farther down. But be sure to dip your cutters in something like bleach before continuing to cut farther down to see whether the next cut will show a healthy stem; you don't want to spread it via your cutters. If you see that you've cut through stem that isn't green, keep dipping and cutting. Just be sure to cut down the branch to a point where everything you see when you cut is green.

One other thing that around here can cause eventual wilting of the entire plant is severe nematode damage. We've never had that at this time of the year, though, so that seems most unlikely. (But if you ever do get that, plant lots of African marigolds all around the rhododendron; we've saved a rhododendron that way.)

Best wishes,

    Bookmark   March 13, 2010 at 3:27AM
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