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  • To: Multiple recipients of list <iris-l@rt66.com>
  • Subject: Nematodes
  • From: Ross <ross@dsrt.com>
  • Date: Tue, 23 Dec 1997 09:02:57 -0700 (MST)

	I have had an opportunity to digest the U. Of Maryland research and
talk to some folks in the field and have some preliminary conclusions.
=46irst, if you want to know more about nematodes per. se., please visit thi=
site (http://ianrwww.unl.edu/ianr/plntpath/nematode/wormepns.htm) It will
give you good general background about nematodes. (There may be another
good site, can't remember at the moment.)
	Last April, researchers at the University of Maryland applied two
kinds of nematodes and two commonly used chemical treatments to compare
results on iris borer. Nematodes used were: Steinernema carpocapsae (known
as Sc) and Heterorhabditis bacteriophora (known as Hb) . Chemicals tested
were:  dimetheoate (Cygon) and imidachloprid (Marathon). These were used on
groups of iris which had be=00=00=00=00=00=00=05en intentionally infected=
 with borer the
previous fall. As I said, the plants were treated in April, and dug up in
mid July. The findings were that one nematode Hb (Heterorhabditis
bacteriophora), dimetheoate (Cygon) and imidachloprid (Marathon) all
eliminated 87% of the borer problem, and Sc (Steinernema  carpocapsae) the
other nematode, did better, eliminating the borer population completely.
	I know many of you have been using Cygon, and given these results,
I want to urge you to consider changing. Cygon is a nasty chemical, rating
very high on the government's LD toxicity list. It's high toxicity is the
reason it works, but on the other hand, using chemicals like this is like
conducting nuclear war on your garden. It kills everything.  Unfortunately,
most of what it kills are beneficial organisms. It is also a little risky
to use. I have often wondered if Cygon wasn't a major contributor to the
reason virgin soil seems to do so much better for iris. Marathon is fairly
new (at least to me), and I don't know how dangerous it is. It is a
systemic poison.
	By contrast with both, nematodes are so safe that the government
does not even bother to regulate their use. Nematode suppliers will also
tell you that nematodes (depending on the variety) will control up to 300
other garden pests, while disturbing few beneficial garden organisms.
(Nematodes are relatives of earthworms.) I find that a fascinating prospect.
The one (sort of) advantage we have with iris borer over other pests is
that we know where to find them. Unfortunately where we find them is in our
iris plants! In the research study, nematodes were applied to a one square
foot area around each infected plant at a rate of 500 nematodes per square
inch (remember that nematodes are microscopic). (The researchers also
tested a 1,000 per square inch rate and found that the 500 rate was just as
effective.) Nematodes are routinely purchased per million, which would mean
that at the 500 per square inch rate, a million nematodes would treat 2,000
square inches. The researchers treated a square foot around each plant (144
square inches), but I think one might be able to do less, perhaps an 8 inch
square around each plant. The reason I suggest this is that normal nematode
rates for broadcast application run more like 4-5 per square foot, so 500
is considerably higher than normal.
	Anyway, using a 12" square, a million nematodes could treat 14
plants. Using an 8" square you could treat closer to 30 iris plants. All
these numbers are approximations because when you receive the nematodes thy
usually come in a damp sponge and you then disperse them in a bucket of
water. The mix is then poured or sprayed over the area you want to treat.
	Although possible, foliar treatment with nematodes does not seem to
be a good option=00=00=00=00=00=00=05=83pinion is not based upon research,=
 however. The
general consensus is that chances of success are greater using nematodes
applied to the soil. A factor to remember is that nematodes don't like cold
soil. So when you treat, for optimal results, make certain that your soil
temperature is at least 50 degrees to a depth of 5". Nematodes will last at
least two months in the soil if there is nothing for them to feed on and
reproduce. I know of one fellow in Vermont who has had nematodes remain in
his garden for six years.
	One of the suppliers used in the study, HydroGardens of Boulder
Colorado (800-634-6362) sells nematodes at $8 per million, 6 million for
$30. Because nematodes are living organisms they must be shipped by two day
air, and this adds about another $7.50 to the cost. Several people or a
club could get together however, and reduce the cost. Biosys of Columbia,
MD, the other nematode supplier used in the study, apparently had
formulated a water dispersable granule for the nematodes which may have
made normal shipping possible. However, they are apparently out of
business. There are many other nematode suppliers around, so shop around. I
can recommend M&R in Durango Colorado (800-526-4075) from personal
experience, I have not checked their prices recently. The fellow who
supplies nematodes to Garden's Alive has an excellent reputation, but at
the moment they are offering a different nematode species than SC.

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