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Re: iris


Can someone tell us(you) how much damage the borer could do in a
>season if the all natural garlic/onion cure didn't work?

The onion/garlic cure is a new one on me.  Since iris borers are highly
specific to irises, I would suppose that planting anything except irises in
ones garden for a season would get rid of your infestation--until the moths
flew in from a nearby garden (it would probably have to be quite nearby as
they are weak fliers).  While I'm no fan of insecticides, I do use them
from time to time.  Our gardens are not natural ecosystems and require our
intervention to maintain them.  As sceptical as I am about insecticides,
I'm equally jaundiced when it comes to "natural" cures, most of which
either don't work at all, or have so little effect as not to be useful in a
garden setting.

This spring I suffered a major incursion of borers and tried to control it
with hand methods, not using Cygon or any other insecticide.  I can report
that there was a great deal of devastation, especially in my Louisiana
Irises, which were essentially ruined.  While redigging the bed, I found
many fat caterpillars and pupae (so one positive thing was that I got some
pictures of them for my book) but am sure I missed many more.  Lesson: next
year use Cygon.  Borer infestations are not common here and if they can be
kept out for two years, spraying can be discontinued until they show up
again.

Cygon is relatively benign if you just restrict it to your irises.  As a
systemic, it  only kills things that feed on the irises and does not harm
beneficial or neutral insects.  The key is wise and infrequent use.  I am
worried, though, about throwing down Diazinon granules, which will kill
every soil arthropod in the vicinity.  Since the borers are in the irises
and do not feed once they emerge into the soil, Diazinon would be expected
to be relatively ineffective.

Listers have reported borers now from sites far outside their range as
given in the World of Irises, as far south as South Carolina and as far
north and west as Iowa.  With more irises being grown, it is not surprising
that the moth may be extending its range.  I would predict that the
extension would take place slowly because of the limited flight of the
adult moth.  A good way of spreading it around would be by the shipment of
infested rhizomes.  Many years ago I ordered plants of Iris albicans from a
dealer who claimed they were imported from Pakistan.  Maybe so, but each
one had its very own borer!  This raises questions--if the borer is really
a North American native, and those rhizomes really did come from Pakistan,
has the borer somehow gotten to Pakistan?  Or is it possible that there are
other borers in other parts of the world, just waiting to get to Europe or
America and devour our precious bodily fluids (Oops, I mean rhizomes!)?

Bill Shear
Department of Biology
Hampden-Sydney College
Hampden-Sydney VA 23943
(804)223-6172
FAX (804)223-6374
email<bills@tiger.hsc.edu>






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