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Environmentally safe weed killer
Name: Maryjean Ricchiutto
Status: Other
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
The black walnut tree disperses a poison from its roots that prevent other
plants in that area from growing. Have scientist developed a synthetic
chemical like that to use as a "weed killer"?
Replies:
I can only provide a little information here. I believe you are referring to
the substance called juglone which as you mention is made by the black walnut
and is given off through both the roots and the tree's canopy. Trouble with
the chemical, which by its nature acts as a hormone, is that I believe it is
indiscriminate as to what it will kill. Most research into marketable weed
killers strives to find those chemicals which (1) are demonstrated non-toxic
to the environment (2) will not persist indefinitely in the environment (i.e.
will break down into other non-toxic substances) and (3) will not be toxic to
all plants (i.e. will be selectively toxic to those plants targeted as
"weeds." Naturally "weeds" are really any plant material growing outside of
its desired location--you might call a rose plant growing in an area where you
intended to grow cabbage a "weed.") I think juglone or a synthetic-produced
version of it might be useful as a weed killer perhaps to kill vegetation
between the panels of a sidewalk, for example. The trouble might be when the
first rain happens after application and when the weather clears, you find the
chemical has gone into solution and killed part of you lawn adjacent to the
sidewalk. Naturally, the dose could be controlled and some sort of chemical
additive might be possible to prevent movement to prevent this. One last
consideration might be: would juglone be safe, after application, to have
people (for example, children) playing or running through bare footed and
getting the material on their skin. This would deal with how the material
might be absorbed into the body and whether it indeed is safe.
Personally, I have planted two walnut trees (in my case English walnut,
Juglans regia) in my yard at home. The trees are currently quite small. I am
not certain whether the substance juglone is produced by the species I have
planted, and I do often check for any killing of the grass directly adjacent
to the trees. No killing has been observed thus far. By the way, it is felt
that the chemical is made by the black walnut to serve as a means of
competition which other plants which might grow nearby and compete for
minerals and moisture. This is Juglans nigra's way of "keeping distance" from
its neighbors.
One last thought is, and YOU might be interested into looking into this is
whether or not the fruit of the walnut (that is the NUT) has ever been
chemically analyzed for its composition. Since the tree does try to kill its
competition using juglone, I often wonder, each time I reach for a walnut-
laced Christmas cookie in fact, whether or not I might be consuming another
chemical which might be designed to be toxic to me. Let me stress I have no
information to support this position, and in fact I hope it is not the case.
Perhaps you could try a search of the literature to see if any chemical
analyses have been done of either juglone or the nut itself.
Rickru
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Update: June 2012
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