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chester_grant

A few Roseum shoots turning brown with leaves wilting

chester_grant
15 years ago

I have now had to remove three or four shoots - new growth this season - where the new green branch has turned brown in the middle with the leaves at the end dieing. This has affected only a portion of the plant - I would guess some kind of root fungus? Recommendations?

Comments (6)

  • rhodyman
    15 years ago
    last modified: 9 years ago

    Terminal buds and leaves turning brown and leaves wilting is symptomatic of Botryosphaeria Dieback, Phomopsis Dieback, Phytophthora Dieback, or Rhizoctonia Root Rot dieback. All four diseases spread rapidly and may threaten an entire plant. They are more active in warm summer conditions. It can also be borer damage.

    1) 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. Prevention with fungicides and careful control of exposure to high humidity may be practical.

    2) 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.

    3) 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.

    4) 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 avoidance of excess irrigation. [Return to Problem Menu]

    5) Ends of branches die when a Rhododendron Stem Borer, Oberea myops, Dogwood Twig Borer, Oberea tripunctator, or Rhododendron Borer, Synanthedon rhododendri, is in a branch. Borers only affect the portion of the plant away from the roots from the borer. If the borer is in the main trunk, then the entire plant will wilt and die. The plant can be save by cutting off the area with the borer and letting the plant regenerate from the roots. There are no conventional insecticides that will kill stem borer larvae once they are inside the branches. The best control option for homeowners with only a few plants is to prune out and destroy wilting branches in early spring or late summer.

    Here is a link that might be useful: Common Problems and Their Solutions.

  • chester_grant
    Original Author
    15 years ago
    last modified: 9 years ago

    Phytophthora cactorum - I am pretty sure this is it.

    I understand I cant plant another rhody or equvalent plant in that area.

    If I get some antifungus or whatever I wonder if I can soak the roots and save the plant? A $100 rhody is an expensive item to lose..

  • rhodyman
    15 years ago
    last modified: 9 years ago

    It could be many things for which the best course of action is to wait and see.

    If it is phytophtohora cactorum, I doubt that you can save it. If the plant is still alive and only a few branches are affected, then the best course of action is to make sure the plant has good drainage.

    You didn't mention whether the plant is stressed by drought, or being pruned, or being recently planted or recently transplanted.

    If the plant should not be stressed by drought, then I would make sure the plant is planted properly, that is that the root ball has been opened up so the roots don't strangle each other and that the site is in good acidic soil that is well drained. Some nurseries will sell a plant that has been recently improperly transplanted to a larger container without opening up the roots. These plants will eventually decline as the roots will eventually stangle each other.

    Usually, when planting, the soil is amended with peat humus or bark dust. These actually help prevent disease as does good drainage. To insure good drainage, plant in a raised bed and never plant deeper than it was planted originally.

    It it has good drainage and the plant has been recently planted, it may just be showing sun burn on the new foliage. After the plant has been established, this should not be a problem except in years when you prune the plant. Then you will always get sunburn on leaves that were previously shaded before being pruned.

  • chester_grant
    Original Author
    15 years ago
    last modified: 9 years ago

    The roseum was planted two years ago and is in a spot where it gets full sun after mid-day - facing west. There are 5 roseums interspersed with conifers dotted along that border in front of a wall topped with a 6 ft hedge of manhattan eunonymous. Those rhodies dry out pretty easily as the roots havent yet established so I have been watering liberaly - thats another reason why I suspect root rot. Although I wonder if it could be a root weevil as I have noticed the eunonymous leavrs in that vicinity have leaves with the characteristic weevil notches..........

  • rhodyman
    15 years ago
    last modified: 9 years ago

    Don't water unless the leaves look dry in the morning. It is normal for the leaves to look dry in the heat of the day.

  • chester_grant
    Original Author
    15 years ago
    last modified: 9 years ago

    Since cutting out the browned wilting parts there have been no more problems for a couple of weeks. Nevertheless I have dug this one up just in case it infects the other roseums in the vicinity. I have planted it in a shady location where it wont dry out as easily

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