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Part of rhododendron seems to be dying

MLau
12 years ago

Good day, I purchased a home last summer that had a rhododendron at each end of the house. Both of them were quite bushy from the ground up so a friend suggested they be pruned. He said he had done so with his and they came out fine. He proceeded to prune them. This spring parts of one of them has two large branches which are having problems with all the leaves falling off and the buds are darker then the seemingly healthy branches. Interestingly enough, one of the branches has a branch that has green and healthy leaves, the rest of the leaves are falling off. Does anyone have a suggestion as to what the problem might be? I have taken pictures if that can help. Thanks in advance for any assistance you may provide. Mel

Comments (15)

  • morz8 - Washington Coast
    12 years ago
    last modified: 9 years ago

    Mel, yes, photos would help. It's normal for leaves of approximate three years old to drop from rhododendrons, but I don't know if that is whats happening with the shrubs being pruned back to older growth - or if you might have something going on like winter bark split or even rhododendron borer.

  • mainegrower
    12 years ago
    last modified: 9 years ago

    Mel: I'm not sure why anyone would want to prune rhododendrons which are growing well and "bushy from the ground up",unless they're blocking a window or something, but what's done is done. If the pruning was done late - after late June or early July in MA - it's very possible that it stimulated a lot of vegetative growth which did not have time to harden off for the winter. This past year was very difficult for rhododendrons throughout New England because of cold and high winds.

    If the leaves which are falling off were curled and brown, winter dessication is likely. A picture would be very helpful, but it's likely that the plants will recover in time. By my reckoning, the season is at least three weeks later tahn normal at this point.

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  • MLau
    Original Author
    12 years ago
    last modified: 9 years ago

    Hello Morz8 and mainegrower, thanks so much for getting back to me. I am new to this site and haven't figured out how to upload images. My buddy pruned the plant because the plant on the left side of the house had been pruned so he thought it would make the plants symmetrical. Have either of you ever uploaded an image? I agree it would give you more info.

    Mainegrower, I grew up in Eastport.

    Thanks again for getting back to me. Mel

  • MLau
    Original Author
    12 years ago
    last modified: 9 years ago

    Good day, just set up this photobucket site to include pictures of the issue. Mel

    Here is a link that might be useful: Mel's photos

  • MLau
    Original Author
    12 years ago
    last modified: 9 years ago

    Here are photos to show the damage. Thanks for taking the time to assist. Mel

    Here is a link that might be useful:

  • morz8 - Washington Coast
    12 years ago
    last modified: 9 years ago

    Mel, 'Mel's Photos' asks me for your password, doesn't allow me to view.

    In clicking on 'Picture of the damage' to enlarge, it looks very much to me like bark split - although that isn't something I encounter in my climate so hopefully rhodyman or mainegrower will be back before long.

    Bark split is injury caused by freezing temps where bark on branches and main stems splits and separates from the body, causing anything above that point to die.

    That's a considerable amoung of damage, removing it is going to leave you with a somewhat abstract shape for at least a good while.

  • mainegrower
    12 years ago
    last modified: 9 years ago

    The bark is certainly split quite dramatically in the center background of the picture. It is, however, very hard to tell from where the healthy green leaves (and flower buds) are emerging toward the back of the plant. Much of the rest of the damage looks like classic winter burn/dessication.

    I assume the plant looked enirely healthy in the fall and I really don't mean to pick on the poor pruner, but if the picture shows the side of the rhododendron with the most intense winter sun exposure, here's what may have happened. The pruning opened up the plant enough to expose bark that had been shaded for many years and this led to the bark split. The split plus the sun and wind and cold did all the damage we see in the picture.

    What doesn't quite fit with this theory is the snow depth last winter. Unless the plant is in a place where snow does not accumulate, last winter's deep snow in New England should have provided a good deal of protection, especially for the bark.

    As morz8 says, you'll have an odd looking plant for a while once you prune out the dead stuff, but it will eventually fill in.

  • earthworm
    12 years ago
    last modified: 9 years ago

    Best time for rhododendron pruning ?
    And how often ?
    My plant is ? old ? , 5 to 6 foot high.
    I suspect the PO never pruned.
    I like doing the "no tool" pruning - whatever snaps off.
    Replies appreciated.

  • rhodyman
    12 years ago
    last modified: 9 years ago

    When: The best time to prune rhododendrons is right after they finish blooming. As with most spring bloomers, rhododendrons start to form the next year's flower buds in mid-summer and by fall the buds are fairly well developed. Pruning in mid-summer or later removes the next year's flower buds. Do not pinch after June because then flower buds will not have time to develop for the following year.

    How: Pruning is seldom needed except for removal of faded flowers, but if it is needed, branches may be trimmed immediately after flowering. There is little need for pruning azaleas and rhododendrons. If growth becomes excessive, reduce the size with light pruning. Plant form can be improved by pinching out the soft, new shoots of vigorous-growing plants. It is best to prune within two weeks of when they stop blooming. This is to prevent removing next year's flower buds. Rhododendrons and azaleas may be pruned after the flowers have faded to induce new growth. Prune out dead, diseased or damaged branches, and in cases where plants have become scraggly, start cutting the oldest branches back to encourage growth in younger branches. Pruning in the fall is not recommended since it will remove the buds for next year's flowers.

    With the larger-leaved rhododendrons (elepidotes), you must prune just above growth joints. Each year as the plant starts to grow there is a visible point where the plant started growth. We call this point a growth joint. Prune just above this point, because that is where the dormant growth buds are located. Don't prune between joints, because there are no dormant growth buds in that area. However, with azaleas and the small leafed rhododendrons (lepidotes), you may prune anywhere along the stem, though you may not be able to see them, these plants have dormant growth buds nearly everywhere.

    As a plant grows, some of the inside limbs will be shaded out and become weak and die. It is a good idea to remove these, plus other weak limbs that are on the ground or crossing over each other. This provides better air circulation and does not provide a place for insects and diseases to start. These branches should be pruned back to clean white wood that is not infected while the weather is dry to prevent the spread of diseases.

    Deadheading: For maximum flower production, pinch off faded flowers or the developing seed capsules that follow [deadheading]. Most successful rhododendron gardeners do not deadhead. It is not because they don't believe in it or that they don't want to do it, but rather because they have so many plants and so many other more important tasks that they don't have time to do it. Does this cause a problem? Not really. Some plants that are reluctant to bloom or have disease problems such as petal blight or in an area that is marginal for the plant in question may benefit from deadheading, but that is unusual.

    Pinching: A friend of mine has the most beautiful rhododendron and azalea garden. All plants are about waist high. From any place in the garden you can see just about every plant. During the flowering season it is awesome. I asked him how he keeps the plants so well kept and his reply was that he just removes the top foliage buds each year with his fingers in the late fall or early spring. This can be done once the rhododendrons reach the height you want. Then each spring after the flower buds start to swell and the smaller leaf buds are obvious, break off leaf buds [pinching] on the top of the plant to prevent it from growing taller. You must be careful not to damage any flower buds. No pruning at all. This technique minimizes disease and insect damage. It works very well for him. It is labor intensive, but well worth the effort.

    Severe Pruning: If necessary, you can remove a great deal of material. It is a general rule to not remove over 1/3 of the leaf area each year. Pruning is generally used to control unsatisfactory height or width of a plant. I don't prune very often and try to limit pruning to plants which have a shape that is unsatisfactory or dead branches. If I want to cut trusses for bouquets, I always cut the flowers in the highest branches since this helps keep the plant within bounds and they are also the best flowers.

    Severe pruning is not uncommon with rhododendrons and azaleas. A healthy plant can be cut to the ground and will usually come back. Rhododendrons and azaleas have dormant buds beneath the bark which sprout to form new growth after severe pruning. However, Richard Colbert reported that such attempts at Tyler Arboretum were only successful if the plant had enough sun light. Those in heavy shade frequently died. He recommend first opening up the shade by thinning the forest canopy. Then he recommends just removing some of the top to induce new growth at the base. Then when that new growth is established, the remainder of the top can be removed.

  • donnaroe
    12 years ago
    last modified: 9 years ago

    I think that two of our rhododendrons have wilt disease. Should we dig these up and discard, or try to replant them somewhere and treat them? I read where it will eventually kill them-no matter what we do. I can furnish a photo if anyone needs one.thanks

  • rhodyman
    12 years ago
    last modified: 9 years ago

    Wilting can be caused by too little water or too much water. Drought damage usually results in dieback of individual branches. Usually watering and cutting back the affected branches will save the plant if caught in time.

    If you mean root rot, then it is normally terminal. It is caused by poor drainage. I don't know where you live, but here we have had lots of rain the past 2 months and areas with poor drainage have problems. The root rot fungus is in the ground just about everywhere. There are varieties that are more resistant to root rot. But even more important is to use a raised bed so that drainage won't be so critical.

    Some disease resistant varieties and their cold hardiness rating are:

    'Aunt Martha' (-10F), 'Blue Jay' (-10F), 'Blue Peter' (-10F), 'Boule de Neige' (-25F) , 'Cynthia' (-15F), 'English Roseum' (-25F), 'Myrtifolium' (-15F), and 'PJM' (-25F)

  • mainegrower
    12 years ago
    last modified: 9 years ago

    donnaroe: Don't be too quick to dig up your plants. If you live in the Northeast, northern New England especially, you've had a long spell of unseasonably cool wet weather. This can cause rhododendrons to put out a great deal of soft, succulent growth. Once the sun and heat hit this growth, it wilts until its had a chance to harden a bit.

    rhodyman is absolutely right about the conditions also favoring various root problems, but there's nothing to be lost and a great deal to be gained by waiting a few weeks to see if things improve.

  • donnaroe
    12 years ago
    last modified: 9 years ago

    Thank you, everyone, who has answered. I believe my rhododendrom has verticillum wilt disease. (spelling?). Can it recover? These two nova zembla have been sick since last summer. The nursery where we purchased them came out in the fall and said that it looked like verticillum wilt disease, and made good on them. We purchased some viburnum to put in their plac. Now I am seeing new growth on these rhodies. They still have some totally dead brown complete branches on them. Should I dip some pruners in bleach and prune off all the dead and replant them somewhere? These are not mature plants-they were $70 a piece and are not that big-I can move them if need be.
    As a final note (if someone can comment), we had some Lees Dark Purple rhododendron planted around our house that died of virticillum wilt about 20 years ago. I read somewhere that this disease stays in the soil. Is this true, and what other plants are suceptable to this disease that I should stay away from? I can try to put pics if anyone wants them. Thank you!

  • rhodyman
    12 years ago
    last modified: 9 years ago

    Verticillium and fusarium wilt is fairly unusual in rhododendrons. Purdue University considers rhododendrons resistant. Ohio State considers rhododendrons to be typically free of this disease.

    There are other fungi that cause dieback in rhododendrons. It probably isn't a root rot since that is usually fatal. Dieback is usually caused by f Botryosphaeria Dieback, Phomopsis Dieback, Phytophthora Dieback, or Rhizoctonia Dieback.

    Botryosphaeria dothidea causes leaves to turn dull green and then brown and roll and droop. Cankers form on branches which may girdle the branch. This is the most common disease of rhododendron in the landscape. A typical symptom of this fungal disease is scattered dying branches on an otherwise healthy plant. Leaves on infected stems turn brown, then droop and roll inward. These leaves often lay flat against the stem and will remain attached. The pathogen can infect all ages of stem tissue through wounds, pruning cuts, and leaf scars. Heat, drought stress, and winter injury can increase disease incidence. Cankers on branches can gradually grow through the wood until the stem becomes girdled. Diseased wood is reddish brown in appearance. Discolored wood viewed in longitudinal cross section often forms a wedge that points toward the center of the stem, and the pith may be darker brown than the surrounding wood. Sanitation and applying a fungicide such as metalaxyl (Subdue) after pruning my provide some control. Plants should be grown in partial shade, with mulch and kept well watered during dry periods. All dying branches should be promptly pruned out in dry weather and all discolored wood should be removed. Plants should also be protected from rough treatment during maintenance activities to prevent unnecessary wounds.

    Phomopsis rhododendri symptoms vary from leaf spots to chlorosis and then browning of leaves which then wilt. Browning streaks extend down the stem to a wound. Fungicides such as metalaxyl (Subdue) should control an outbreak. Sanitation and applying a fungicide after pruning may provide control.

    Phytophthora cactorum causes the central vein of a leaf to turn brown and the discoloration extends to the petiole on tender new growth. The infections spreads outward from the midrib tissue and the leaf wilts. Infections are more severe on azaleas. Some varieties of rhododendrons are vulnerable (Chionoides, Catawbiense Album, Nova Zembla) and some are resistant (Roseum Elegans, Scintillation, PJM). Control of the disease is difficult. Since the infection goes from the roots to the tips, when you see the symptoms it is too late. To prevent it, use a raised bed with lots of sphagnum peat moss. Also, keep the mulch back 2 to 3 inches from the stem. Prevention with fungicides and careful control of exposure to high humidity may be practical.

    Rhizoctonia solani: causes small necrotic spots on leaves, which later become dark brown or black. Defoliation follows severe leaf spotting. The fungus is omnipresent in the soil and appears to be most virulent at high humidity levels. Microscopic examination of roots and crown are the surest diagnosis. Cultural practices to control this disease include improvement of drainage and avoiding excess irrigation. It seems to only be present in irrigated beds such as at nurseries. Nurseries now have a chemical-free way to prevent Rhizoctonia; a hot water treatment.

    Rhizoctonia Web Blight causes dieback of interior leaves of compact tightly-growing azaleas within irrigated landscape beds. Rhizoctonia web blight is often seen during the warmer, humid summer months. Infection begins in the interior of the plant as the fungus survives in the soil or container rooting medium. Infected leaves develop brown lesions and eventually the entire leaf will brown and separate from the stem. The affected leaves often remain matted together by the fungus´s web-like growth (hyphae) that holds the brown leaves within the canopy. As the temperature cools in the fall, the fungus stops growing and the matted leaves drop from the plant. The disease is only a problem in landscape azaleas that are sprinkler irrigated. Wet foliage and high humidity favor infection. Use drip irrigation or soaker hoses to irrigate landscape beds. Also, remove fallen leaf debris from beneath plants. Fungicides can provide some control but should not be relied upon solely. Apply fungicides at the first sign of disease and continue through the summer months.

    The Department of Agriculture Research Service has found a prevention. Plant pathologist Warren Copes found placing the cuttings in water at 122 degrees Fahrenheit for 20 minutes is the most effective method to eliminate Rhizoctonia without damaging the plant, thus eliminating the need for fungicide treatment. The pathogen can be eliminated in less time when placed in water at higher temperature, but the risk of damaging the cutting increases. According to Copes, there is still potential for the cuttings to be re-contaminated in other areas of the production process. He is trying to identify which steps pose the most risk for re-contamination, with the goal of maximizing control of this fungal disease with the least amount of effort and expense for producers.

    Here is a link that might be useful: How to care for rhododendrons

  • MLau
    Original Author
    12 years ago
    last modified: 9 years ago

    Hello everyone, I have been sidetracked trying to get our seniors graduated from school and during that time my rhododendron is making a comeback. There are leaves and blossoms beginning to show themselves. The buds are slowly opening up and leaves are sprouting along the branches. Perhaps it was the positive karma you all sent. The guy who pruned the plant is now walking around saying "I told you so." Hmmm, I am just glad it is recovering. Thanks to all. I will use some of the pruning techniques some of you mentioned, but I think I might leave it alone this year. Mel

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