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snails

More than you really wanted to know about snail & slug control:

I was interested to read the report from the person who tried encircling
his/her snails with copper as a test of its efficacy since that is exactly
the way the experiment was done by Dr. Koehler at the University of
California in the mid 80's.  Great minds think alike.  UC tested copper
screening, 6" wide, in an ideal setting(plastic sheeting placed over
asphalt with a board to provide the critters with shade).  He also tested
diatomaceous earth, hardwood ashes, softwood ashes and sand.  Several
materials worked pretty well.  The ashes actually kept more snails inside
than the copper or DE.  (Hardwood 93% captured;  softwood 89%;  copper 87%;
DE 76%; sand 19%)  In a second trial the DE caught 91% when compared with
a relatively ineffective forest product called Snailproof(ground incense
cedar).  The last product may be trying out the same principle as the
gorilla hair that someone mentioned.

The reason that copper came to be the organic material of choice was the
simple fact that everything else tested is ruined by rainfall, a definite
disadvantage with those aqua-phillic mollusks.

All the available copper products, to my knowledge, contain some zinc.  The
UC study bought theirs off the shelf and it contained 30% zinc. If you're
thinking of ringing you veggie garden with copper the general
recommendation is to use screening at least 4 inches wide nailed to a
board.  The board should be sunk in the ground about 2 inches to prevent
the snails from digging under.(The entire 4" of copper would be above
ground, the wood would be sunk.)

One researcher gave detailed instructions for using copper around trees.
Since there was some discussion about trees I thought it might be useful to
quote him at length:
        "There are basically two ways of applying the copper as barrier.
The trunks can be painted or sprayed with a slurry of copper bordeaux
mixture.  The width of the copper band should be at least six inches and it
is applied between ground level and the first branching.  Since this
material is relatively soluble, rain and irrigation water can wash it away
after about one year.  A small percentage of white latex house paint, or a
good spreader/sticker may be added to increase the persistence of the
copper.
        For a more permanent barrier, a copper foil...is wrapped around the
trunk....One end of the foil is stapled to the tree, then the foil is
wrapped around and fastened with a nickel plated paper clip.  Several extra
inches of foil are left to allow for expansion of the trunk.  These
barriers have been found to last more than five years.   However, in some
areas, birds and other small animals tear the bands off the trees,
presumably seeking food such as insects which hide between the foil and
trunk.  Inspections must be made to see that the bands are in place and
working properly."


Every study that I've read reported that the scientists don't really know
*why* copper/zinc works as it does but some of our learned members have
obviously contributed astute speculations.

You may be interested to know that there are some other 'organic' or IPM
techniques in development.  One British researcher mixed bran with chelated
iron(essentially a special kind of soil) and got very good results.  He
tried it in a trial side-by-side with the leading commercial
product(metaldehyde) and the chelates were superior.
Another researcher has successfully used predaceous
nematodes(*Phasmarhabditis hermaphrodita*).  He had to dig them into the
soil a little bit to prevent them from drying out but with that provision
they worked well.  I don't have my catalogues at hand but I *think* that
species in available by mail order from some of the companies that sell
predaceous insects and such.  Unfortunately if you've ever tried to use
predaceous nematodes to control pests(the most common one is used on peach
tree borer) you know that they cost a bundle.  I'd guess that they'd cost 5
to 10 times as much per square foot as metaldehyde.

Forgive me for belaboring a subject that probably isn't officially within
the purview of the group but I couldn't help myself.
Jerry Heverly, Oakland, CA
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