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please help rhododendron problem

Posted by Robes22 NH (My Page) on
Sat, Oct 19, 13 at 14:32

Please help. I went to check my Cunningham white rhododendrons. I have 11 of them and they all have the same problem. The foliage is much less dense than last year and the tops of all the stems have turned a burnt brown color. Please are the pic. This is the second year that I have had them. Last sting the put out a good number if flowers. Please help a large number of the leaf groupings at tops of the are gone or shriveled up like a thread


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RE: please help rhododendron problem

More pics


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RE: please help rhododendron problem

Pics


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RE: please help rhododendron problem

I don't think they were watered as much this year as they were last year. Could that be it? Will they survive?


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RE: please help rhododendron problem

I don't think they were watered as much this year as they were last year. Could that be it? Will they survive?


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RE: please help rhododendron problem

The pictures show all the characteristics of too little water. The browning of the stems is completely natural as is the yellowing and shedding of some of the oldest lower leaves. When faced with dry conditions, rhododendrons shed the lower leaves first. In this case, quite a few more than just those which would have fallen naturally. This is the reason for the bare stems and smaller size of the remaining leaves.

'Cunningham's White' is one of the toughest and most disease resistant varieties, so survival is pretty much guaranteed. Even this variety needs adequate water, however, especially when it grow in competition with sizable trees as seems to be the case in the photos.


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Wow, I'm glad a I read this post. I have a Percy Wiseman doing the same thing. I tried giving it some water a month or so ago, we've gotten 7 inches of rain since, but it was too late I think. It lost all of it's leaves except this year's and now about a third of it has Phytophthora.


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RE: please help rhododendron problem

Phytophthora root rot can occur in rhododendrons planted in the ground, but is far more common in pots because of high soil temperatures in that environment. It's a disease that nurseries treat for routinely because it can be so devatating. The loss of lower leaves can be completely natural or the result of both drought or excess water, not necessarily a fungal root infection.


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So its almost November and every morning I wake up there is a frost. Am I right in that I should not water them now eventhough they received too little water in the summer. And just wait to water them in the spring?


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"Phytophthora root rot can occur in rhododendrons planted in the ground, but is far more common in pots because of high soil temperatures in that environment."

Not that I doubt this can happen sometimes, but, in my several foolhardy attempts to grow various big leafs like R. rex, they didn't die until they were planted out in the ground. I kept the pots in almost 100% (w/respect to direct light hitting the pot) shade, on a clean paved surface at the north side of a building. Maybe they got 30 minutes of early morning sun at most.
I don't believe Phytophthora naturally occurs - or maybe I should just say occurs - in any commercial potting or peat mix. It's either not there or they sterilize it. So your disease free plant from RSF, put in a disease free mixture, doesn't face innoculation...yet. OTOH the spores spread around a garden quite easily. At least 5 root rot sensitive plants survived at least a year for me in their pot, but died w/in the first couple years they were planted.

"It's a disease that nurseries treat for routinely because it can be so devatating."
Again I have no doubt someone like Monrovia might pump their Ericaceous plants full of fungicide. But the manager of a certain renowned east coast specialty mail order retailer assured me they do not routinely treat any of their rhododendrons with fungicides.

FWIW some Cunningham White's I keep for the very utilitarian purpose of serving as rootstocks have survived horrid abuses in pots - lack of watering, over watering beyond my control (i.e., Hurricane Irene) very well. Not to mention 2 incredibly hot summers (2011, 2012). I doubt anything they face in NH, in summer at least, should really challenge them. How long ago were they planted? To me they do not look too bad if you they experienced a dry summer and were only planted w/in the last 3 years. I've had plants recover from looking much worse.


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ok I see now

planted 2 years ago
Yeah...as long as you made sure to tease their roots out of the pot mold, didn't plant them too deep, cut any circled roots, etc...I wouldn't worry about them. I personally believe a little bit of drought forces a plant to have to get better rooted than if you ran to it with a hose during every dry spell. I have a 7 year old 'Vulcan' that has survived bone dry soil several times recently. Never watered it past its first year. I would only worry about watering them _now_ if you are still in the midst of a drought.

This post was edited by davidrt28 on Tue, Oct 29, 13 at 22:17


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RE: please help rhododendron problem

  • Posted by morz8 Z8 Wa coast (My Page) on
    Wed, Oct 30, 13 at 0:07

Robes, if your Fall has been dry, go ahead and water, never mind that you've had frost You want the soil completely moist before really cold weather takes place.. Watering after frost won't reduce winter hardiness, it will help - not harm - your plant.


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RE: please help rhododendron problem

In regard to davidrt28 comments about the spread of phytophthora. It's no doubt true - let's hope - that commercial potting mixtures for rhododendrons are sterile and phytophthora-free when their containers are first opened. As soon as the mixture is placed in a container and exposed to the environment it can be quickly infected. Wind, wind driven rain, contaminated water sources, contaminated surfaces on which the pots are placed, are all possible sources of infection.

Your success with large leaf rhodoendrons in pots is very likely due to the low soil temperatures acheived in a shady environment as well as an extremely free draining potting mix. Planted out in a less than ideal environment the infection, whether previously present in the pot or encountered in the new planting environment becomes far more virulent. Root rot prone species need an almost 100% organic planting area raised above grade to provide optimum drainage, very careful attention to watering in order to avoid both too much dryness and too much moisture. Even with the best of care success is not assured, as I well know. There is really nothing that can be done about sudden uncharacteristic hot spell. The one I experienced last July allowed root fungi to do a great deal of damage.


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RE: please help rhododendron problem

So the general opinion after looking at the pictures of my Cunningham white rhoddys is that their brown stems and lack of leaves is due to lack of water and they should make a full recovery?


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"Root rot prone species need an almost 100% organic planting area raised above grade to provide optimum drainage,"
Yes. Not that I didn't ignore many opportunities to learn this lesson years ago, but in future ALL of my rhododendrons...except maybe something like a R. hyperythrum hybrid, will be planted on mounds. It just saves trouble down the road. OTOH, in the period around Hurricane Irene I had almost 40 inches of rain in 40 days. Granted, that might be a once or a twice in a lifetime experience. A large R. rex I drove in from the PNW died in these conditions, and its possible no amount of mounding would have prevented it. The soil was simply 100% saturated and bath water warm for too long. My longterm approach to that species is going to be to try to graft it onto R. maximum X R. calophytum. One survived that innundation, in a spot where water was slightly ponding, with no ill effects.


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A couple points:

First, Phytopthora is not the only or the most prevalent cause of rhododendron death.

Second, the rhododendron nurseries I am familiar with do not use chemicals to prevent Phytopthora. They use a media like bark dust that doesn't retain water. In fact this super draining material requires that the plants are watered every day.

Third, commercial nurseries do get Phytopthora, not very much, but it does happen. Their plan is to quickly spot and destroy the infected plants before they infect other plants.

Fourth, the most common causes of death are to underwater plants in pot and to not open up the root structure of root bound plants taken out of pots.

Fifth, yes, raised beds and well drained planting sites are very important also.


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RE: please help rhododendron problem

Robes22: I think you're correct in your understanding of the general consensus.

davidrt28: Grafting does offer an excellent solution for highly susceptible species. It's somewhat surprising that no American nursery - at least to my knowledge - has explored this option since it is such a common practice in Europe. It would add considerably to the retail cost, but I think dedicated rhododendron gardeners would be willing to pay it.

It would be great if we were able to duplicate the non-water retaining characteristics of pure bark as used in pots in the landscape, but sooner or later earthworms and other soil organisms alter it and that superb drainage is lost.


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First, Phytopthora is not the only or the most prevalent cause of rhododendron death.

Well, true but given that phosetyl-type fungicides have generally been protective for me (I kept a Trewithan Orange alive for 3 years, experimentally; it died when I discontinued) it safe to assume what kills rhodies in hot, moist soil is Phytopthora or a related oomycete (water mould; not actually a fungus even though we refer to agents acting against them as fungicides) Pythium is another one that infects plants.

"but sooner or later earthworms and other soil organisms alter it and that superb drainage is lost."
Yeah this is the problem with people thinking they are improving their soil with organic matter. In all likelihood their soil was not as bad as they thought it was, and once the plants are established a lot of the organic material they added will be gone though some will continue to cycle in from decaying leaves, mulch or whatnot. If you want to permanently alter the structure of clay soil, you have to use something like Turface, which is what sporting field and golf course managers use. You can say that they have nothing to do with ornamental horticulture but they do have to keep a demanding plant organism looking green and healthy as it gets trampled daily. Aeration and good drainage is part of the key to that. Of course many golf courses just use sand and water every day, too.


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Rhododendrons will die in wet conditions even if phytopthora isn't present. Just lack of oxygen to the roots will kill them. My rhododendrons stay alive with no fungacides and no raised beds. I test soil drainage before planting. I make sure the soil will pass this test. I do have springs coming up in my yard, so I have installed a drainage system underground to keep the area from being a swamp.

Fungicides, pesticides and herbicides aren't an option for me. We have a large yard and a very shallow hand dug well. Any chemicals we use can get in our drinking water. I do use roundup, mainly to get moss going where I can't mow or mulch. The most dangerous part of roundup is the spreader-sticker they use which is basically a soap.

I have only watered my plants a couple times in 45 years. I do loose branches during periods of drought from fungal dieback. But I remove the infected portion and the plant ends up being stronger.

Before I planted most of the rhododendrons I planted shade trees, so they tend to buffer the harsh sun and hot summers. Otherwise, my plants would be in full sun on a south facing hillside.

Here is a link that might be useful: Testing soil drainage before planting


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"Rhododendrons will die in wet conditions even if phytopthora isn't present...lack of oxygen to the roots will kill them."

No doubt this is a useful reminder. But it's true of most plants other than things like bald cypress. Rhododendrons are notable for an extra sensitivity to this problem, almost certainly related to pathogens. I have camellias thriving in places that aren't exactly low-lying, but are on flat ground that doesn't drain well (even though, yes, camellia enthusiasts say they need drainage too) during the torrential downpours I tend to have from July to October. It's hard to imagine rhodies doing well under similar situations. Along similar lines I noticed out west along the Pacific that rhododendrons seem less sensitive to planting aspect...not exactly growing in swales but not needing to be on high spots either. I surmise that because of the lack of conditions favoring root rot out there, they can get away with this. Their innundations occur in winter when the plants are dormant anyhow.

OTOH could there be a bald cypress like rhodie? Remarkably I had a Rhododendron delavayi for breeding* whose 14"X14" pot was left in a non-draining display box during Hurricane Irene. It was concealed in some shrubbery and with the semi-disastrous conditions at my place: power out for almost 72h, cellar flooded, several large branches down, I forgot about it. It's roots were *completely* underwater for roughly 72h. Amazingly it survived the unscathed and had absolutely no top dieback!

* not a long term outdoor plant here though I'm sure it would survive milder winters like the last 2. My goal is to breed a tree-like zn 7 hardy, semi-sun tolerant red rhododendron. Here at least R. arboreum/R. delavayi seems relatively sun tolerant, and in maritime climates like New Zealand they grow in full sun as specimen plants in lawns.

This post was edited by davidrt28 on Sat, Nov 9, 13 at 15:30


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"Fungicides, pesticides and herbicides aren't an option for me. We have a large yard and a very shallow hand dug well. Any chemicals we use can get in our drinking water. "

I completely agree and I have no interest in plants that will require long term chemical care, which is why I'm trying to figure out how to graft particularly sensitive varieties. Though if you are concerned about this I hope you buy organic produce because, for example, reading about the anti-oomycete compound mefenoxam you see that it can be used on things like strawberries and peppers up to one day pre-harvest.


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What is strange is that most natural inorganic fertilizers are considered "organic" and most organic chemicals are not unless they are naturally occurring in manure.

I have an "organic house", it was built in 1820. Modern houses are a nightmare with formaldehyde and many other nasties. Most people that buy "organic" produce sleep in toxic fumes like formaldehyde, the new house smell.

"Organic" is not always good. Most episodes of poisoning come from natural organic contamination like listeria, salmonella, E coli, rotavirus, and giardia. Chemical fertilizers are much safer. I don't use any fertilizer unless there is a problem and then I use something like cotton meal.

The term "organic" is of very little value because it can mean just the opposite. Also natural includes castor beans, daphne, lead and arsenic which are all lethal. So "organic" and "natural" can be very misleading generalizations and can lead to serious mistakes. The answer is common sense and not misleading labels. If something is pesticide free, say pesticide free.


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RE: please help rhododendron problem

  • Posted by bboy USDA 8 Sunset 5 WA (My Page) on
    Sun, Nov 10, 13 at 14:39

Instances of chemical fertilizers (and pesticides) having been found to contain toxic components not on the label have been reported.

Like other heaths wild rhododendrons are often typical of elevated positions or sites otherwise not involving a large percentage of fine textured soil particles that reduce air levels in the rooting environment. Descriptions of Asian species coming from rainy areas list native growing locations as places like cliffs, logs, stumps and trees over and over again. In my region the native Rhododendron macrophyllum is seen on very coarse looking, often stony soils (where it may also be foggy) and R. albiflorum occurs on mountain slopes where there may often be rock slides in the vicinity.

Hot + wet = rot, you generally can't grow any rhododendrons other than adapted types of evergreen azaleas in the deep South no matter how much shade and drainage you give them because the intense climate keeps the rooting environment unsuitable.

Why is it okay to abuse potted stock because it is going to be grafted upon? The finished combination still has to have a good root system at final planting time in order for a satisfactory outcome to be achieved. During peak spring sales periods outlets here are full of expensive grafted novelties with terrible roots; much of this material comes from a pervasive wholesale grower that makes a big deal about their growing systems and plant quality in their publicity campaign.

This post was edited by bboy on Sun, Nov 10, 13 at 14:45


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RE: please help rhododendron problem

"Why is it okay to abuse potted stock because it is going to be grafted upon?"

Haha, was that directed at me? Well, it's never ok to abuse any plant, but that doesn't mean I'm not sometimes a deadbeat plant owner. When I'm in a rush with watering and care in general, I tend to think about the rootstock plants "oh, they're just for root stocks" and prioritize rare cultivars that are hard to obtain. I've never made it a secret that I'm a lazy gardener.

"Descriptions of Asian species coming from rainy areas list native growing locations as places like cliffs, logs, stumps and trees over and over again." You definitely raise a good point here. Some of these native rhododendron haunts are absurdly rainy in summer, sometimes less so but still with much lower summer temps and higher rainfall than we are used to on the east coast of the US. I got a taste of what a very wet summer could do for Asian BLEs this summer, it was nice! I had above normal rainfall in every summer month, well above normal in some months like June, that was over 2X normal. In fact I didn't have to water anything this year - including stuff in pots - until a brief dry spell around late Sept/early Oct, but by that point days are so short and cool that one watering goes a very long way. It was a nice change from the prior 3 summers, which all had bad droughty periods and were probably the hottest stretch of summers in the mid atlantic since the 1930s.


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