Witches Broom Condition

This time of year, I drive around looking at all the trees with their leaves off and I study the branching structure of them.  One common condition that exists is Witches Broom.  It is considered a disease, but I call it a condition since I think of diseases having a pathogenic organism creating them.  The Witches Broom I am referring to is caused by salt.  Here are a few pictures.

Tufted growth from highway salt spray

These photos were taken along the side of a roadway where salt is used to melt ice in winter.  The cars spray up brine and it coats the trees all winter.

Tufted growth habit

Many buds grow with no distance between them

 The salt damages the terminal bud on the branch.  That bud, in usual situations, subordinates the proximal buds by the production of the plant hormone Auxin.  Auxin is a group of hormones with numerous functions.  The function here being the production of a strong terminal growing bud that extends the length of a healthy branch each year.  Without a healthy terminal bud producing Auxins, the lateral buds break and grow into a disorganized tuft of small branches called Witches Broom.  There is no cure for this except for pruning out the tuft.  If no more salt spray occurs, a bud will start a new elongating branch and will grow more or less normally.   

Given the salt spray situation these young trees grow in, they are going to grow little each year and have a stunted habit.

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1 Comment

  1. Kevin said,

    January 9, 2010 at 6:32 PM

    Oo very cool


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