Could this be root rot on my rhododendron?
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.