North American Fruit Explorers mailing list at ibiblio

["Lucky.Pittman@murraystate.edu" <Lucky.Pittman@murraystate.edu>]

Alan,
I've got no doubt but that pecans do produce juglone,
though all the scholarly writings I've seen indicate
that it is in minimal amounts - at least compared to
J.nigra.  Saw something in print somewhere, sometime,
suggesting that of the Carya species, C.ovata -
shagbark hickory - was the worst offender, insofar as
juglone production was concerned.  
I've always wondered how much of the 'juglone
toxicity' effect was actually due to the direct
effect of juglone, and how much was due to the
ability of the roots of a big mature black walnut(or
pecan, for that matter) to outcompete smaller
plants/trees for available water & nutrients - as
well as shading them.
When you've severed the roots of these pecans and
seen a concurrent improvement in the lot of the
peaches, is it because you've caused a reduction in
juglone, or removed a significant degree of root
competition?

Growing up in east-central AL, there were plenty of
big old pecans all around the farmstead, including a
number of sizeable seedling trees that had popped up
in the fencerow surrounding my grandmother's garden -
as well as a number of seedling landrace-type
peaches.  I never really noticed any significant
effect on the peaches or vegetables from the pecans,
but I might not have noticed it if it had been there
- and the pecans have the potential to still be there
200 years from now, but all the peaches are now gone.

I also had several pomegranates I'd started from
cuttings as an 8 yr old kid, but I'd planted them
about 15 ft from the trunk of what was then a young
eastern black walnut - I didn't know anything about
juglone then.  They grew, without fruiting, for
nearly 30 years, until my parents had to replace the
drain tile from the septic tank, necessitating
trenching right between the walnut and the
pomegranates - all but killing the walnut.  The
pomegranates have borne heavily, on a yearly basis
ever since.

Make of it what you will....

Lucky Pittman
Hopkinsville, KY


------- Original Message -------
>From    : Alan Haigh[mailto:alandhaigh@gmail.com]
Sent    : 1/11/2009 11:35:12 AM
To      : nafex@lists.ibiblio.org
Cc      : 
Subject : RE: [NAFEX] alleopathy of Carya sp.

 I manage an orchard which is adjacent to 2 very old
northern hardy pecans.  The soil is shallow and at
the orchards closest proximity to these pecans there
are a group of peach trees which have failed to grow
well at all.  I notice that the pecan roots look and
smell very similarly to black-walnut roots and have
come to the conclusion that they may well be the
cause of this faulty performance.

 
When I first arrived at this site years ago, I was
asked to replace peach trees that had died in this
spot.  I broke up a considerable amount of soil,
severing competing roots some distance from the trees
and these trees grew as vigorously for 2 or 3 years
but than began to runt out.

 
I was unfamiliar with pecan trees so it was a while
before I identified them (noticed very small pecans
at their base).  Once I decided that my problem could
be alleopathy I took a metal spade with a long handle
and long blade (King of Spades) and trenched a couple
of feet down in about 8' diameter circles around each
peach tree.  After this the trees became vigorous
again for a year but runted out later and didn't
respond the next time to this treatment.  My theory
is that the roots of the pecans are now well
established beneath the depth I am reaching.  To go
still deeper is not practical.

 
My question to you out there with more experience
with pecans is whether you've had similar
difficulties growing peaches under them.  Other trees
in the orchard, even apricots and cherries just as
close, have not suffered to the same degree (if at
all).  Am I even correct that Carya sp. have the same
alleopathic tendency as Juglans?  My google search
seems to indicate that to be so but I was unable to
find specifics before running out of patience.

 
I also have had the same problem with brambles on the
same general site where there is another very large
pecan nearby and black pecan roots visible where the
berries are planted.