Rhododendrons: Juglone persistance in soil

Discussion in 'Ericaceae (rhododendrons, arbutus, etc.)' started by MXB, Jun 20, 2006.

  1. MXB

    MXB Active Member

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    Hi,
    I am going to take down the 20 ft tall, 20ft wide Black Walnut in my garden as everything around it is dying because of the Juglone and/or root system (I clean up the husks and leaves but to no avail).

    I have 3 big rhodos that I would like to move into this newly cleared area in the fall.

    Does the Juglone persist even after I've killed the tree? Or does it dissipate quickly once the tree is dead? Any insights are appreciated. I am going to grind the stump out.

    Thx

    MXB
     
  2. Raakel

    Raakel Active Member

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    Hello,

    Here is a link for an article which discusses the topic in detail. Very interesting reading. On page 8 there is reference to Black Walnut. The article states that juglone persists for up to one year after the tree has been removed. Ericaceous plants, such as rhododendron are particularly susceptible, so I would be patient in planting them.

    Raakel
     
  3. mr.shep

    mr.shep Well-Known Member 10 Years

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    I've grown Rhododendrons under the canopy of an
    English Walnut but far away from or so I thought
    of the roots. Depending on the age of the tree and
    how long it takes for the roots to die out, you can
    figure that the juglone will persist in the soil for
    longer than a year. What you will not have once
    you take out the tree are the elements that have
    probably the highest concentration of the juglone
    in them to contend with later.

    Walnut-Rhododendron compatabilty

    Jim
     
  4. jimmyq

    jimmyq Well-Known Member 10 Years

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    Hi Raakel, the link doesnt seem to flow through, it bogs at the home page for the link.
     
  5. Daniel Mosquin

    Daniel Mosquin Paragon of Plants UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    I spoke with Raakel - she'll find the article again and post a summary of it on Monday, since the site is subscription-only access.
     
  6. jimmyq

    jimmyq Well-Known Member 10 Years

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    thx Daniel
     
  7. NiftyNiall

    NiftyNiall Active Member 10 Years

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    From my reading about the subject, I remember that it was variously reported that the Juglone compounds persisted in the soil, from 8 to 25 years,(probably Dependant on the trees age). Handle Walnut tree parts, with gloves.
    The juglone compounds, are activated by light, and will stain your skin brown,(photodermatitis).
    Nothing I have come across will remove the colour, accept for waiting for your skin to shed,(which it does continually).

    The Juglones, certainly do inhibit many plants, for quite a while, even placing pockets of earth, over top of the roots, and then planting; the inhibitory effect appears to translocate through,(pers.obs.)
     
  8. Raakel

    Raakel Active Member

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    Hello,

    Sorry about the link. I was working on a UBC computer and forgot about the accessibility of some scholarly articles. I took the information provided from an article titled "The Role of Root Exudes and Allelochemicals in the Rhizosphere" by Cecile Bertin, Xiaohan Yang & Leslie A. Weston of Cornell University in the journal titled "Plant and Soil". There is section describing Black Walnut specifically which states the following: "Plants sensitive to the presence of walnut in the landscape and garden include tomato, potato, pea, pear, apple, cucumber, watermelon, bean, garden cress, corn and many ornamental ericaceous species such as rhododendron and azalea." ...and

    "Since juglone is not particularity water soluble, it does not readily leach through soil settings, but instead can persist underneath the tree canopy where living roots are located. After walnuts are removed from a site or die, toxicity can persist for up to one year following removal, due to the persistence of juglone in the soil."

    It was difficult to find much information about the allelopathic effects of julone after the tree was cut down. In the text quoted it states that juglone does not readily leach the soil. So one questions what breaks it down. There is a lot written about the degradation of juglone by soil bacteria. A second article titled Degradation of Juglone by Soil Bacteria by S.K. Schmidt of the Department of Environmental, Population and Organismic Biology at the University of Colorado, states that Juglone will be metabolized at a rate that is directly proportional to both the concentration of juglone and the size of the microbial population mineralizing juglone. This is also a function of the amount of air in the soil, as the bacteria function only in aerobic conditions. So it seems safe to say that the length of time in which the juglone degrades in the soil also has to do with the aeration of the soil and the amount of bacterial in the soil (which naturally occur in the presence of juglone).

    To play it safe I would wait longer than a year to plant your rhododendrons. If your tree has already been removed wait until the fall of 2007. If you cant stand to look at bare ground, or you want to prevent the invasion of opportunistic weeds, chose plants which are tolerant of juglone.

    Raakel
     
  9. MXB

    MXB Active Member

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    Superb info. Many thx to all ;-)

    MXB
     
  10. cowboy

    cowboy Active Member

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    You might want to check with woodworkers in your area. A 20' oak could be put to use. There may be people with portable sawmills that would be willing to come out to cut it up. A phone call or two should give you some information on this option.
     
  11. Dixie

    Dixie Active Member

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    black walnut wood is highly valuable. good suggestion from cowboy.
     

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