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Re: CULT: Marigolds and Nematodes.

From: John I Jones <jijones@ix.netcom.com>

RYFigge@aol.com wrote:
> Good Grief~!  No one told me I'd need to turn the end -of- the- season -
> marigolds under the ground!!!  Sob=sob-gnashing of teeth!  Are all those years
> of marigolds wasted?  Of course they were decorative, if not useful vs
> nematodes.  That is some recompense. but waste makes me sad. 


I wouldn't go off sobbing yet, (well maybe, but for a different reason)...

(long post follows - delete at your pleasure)

In all my years of vegetable gardening (that is, of course before, irises took
over), I never once heard that you have to grind up the marigolds and till
them in to make them effective. So I went searching in my library and found
the following quote in "CARROTS LOVE TOMATOES - Secrets of companion planting
for Successfull Gardening." June 1982 p101 by the Garden Way Press  (****s
added by me)

"Marigold (Tagetes). These strong-scented beauties are very bene-
ficial in discouraging nematodes which attack potatoes, straw-
berries, roses and various bulbs, especially if they are grown for
several seasons in ground where nematodes are suspected. Experi-
ments by P. M. Miller and J. F. Ahrens at the Experiment Station
in New Haven, Conn. have shown that marigolds suppress mea-
dow nematodes for up to three years, and control one or more
other nematodes for one or more years without injuring the
An easy way to use marigolds for nematode control is to rotate
plantings of marigolds with crops that are susceptible to nematode
injury. To lessen competition it is also wise to interplant mari-
golds two or more weeks after the plants which they are grown to

Marigolds control nematodes by producing a chemical in the
roots which kills them when it is released in soil. It is produced
slowly so the marigolds must be grown all season to give lasting
control. Interplanting them may not greatly help garden plants
during the first season, but the benefits become apparent the fol-
lowing years, since the nematode population is reduced.

Tomatoes interplanted with marigolds will grow and produce
better. Plantings with beans help protect against the Mexican
bean beetle, while they help deter weeds and may be planted as a
crop against invasions of ground elder, bindweed and ground ivy.
The older types with strong odor in both foliage and blossom are
considered the most useful.
Pot marigold (Calendula officinalis) or calendula planted in the
vicinity of choice evergreens will repel dogs. This is an old-fash-
ioned herb whose dried flowers were used by our grandmothers to
flavor soups."

So it may also be true that chopping them up at the end of the season helps,
said chopping and incorporating might release more of the chemical in the soil.

They also say on p114:

"Nematodes. These microscopic nuisances are discouraged by
marigokls, scarlet sage (Salvia) or dahlias (Dahlia). Soils rich in
organic matter discourage nematodes, while asparagus is a natural
nematicide. Tomatoes grown near asparagus thus are protected,
while in turn the tomatoes protect the asparagus from the aspara-
gus beetle."

So maybe just the act of adding organic matter (chopped up marigolds) is what helps.

Then I went to my other bible the "SUNSET WESTERN GARDEN BOOK" p541 May 1989:

"It is widely believed that marigold roots can entrap, destroy, or repel
nematodes. University tests discount this belief."

It is now 10 years later, maybe, somewhere, someone knows the "real" answer.
So I went searching the web (with the caveat that you daresent believe all you read).

Searching for "nematodes AND marigolds" to try to get only listings that
contained both words yielded over 200 references, some of which are cited below:

The Novascotia Agriculture and Marketing Berry Crops Newsletter, Number 1,
July 31, 1996 sez  (no source cited)


Research in California, New York, and The Netherlands has shown that marigolds
will kill nematodes (microscopic
worms which damage the roots of many plants, including strawberries). The
roots of the marigolds produce a chemical
which is toxic to the nematodes.

Two varieties of marigold, specifically bred and selected for nematode control
are being evaluated at Bill Wood's
strawberry operation near Tusket in Yarmouth County. The two varieties are
Nemakill from California and Nemanon
from The Netherlands.

These two varieties were planted on June 19 in two separate blocks on a field
that had a high root lesion nematode count.
They require at least 100 days of growth in order to knock down the nematode population.

In mid October, they will be mowed and ploughed under and additional soil
samples tested to compare the before and
after counts.

And from the New York Post (Once again no source cited):

Around The Garden
New York Post - June 1, 1997
C.Z. Guest

Make Room For Marigolds

It's true: Marigolds really can drive off some species of nematodes, those
unwelcome teeny, weenie, worm-like creatures that damage plant roots.

The French and African varieties are the ones to grow -- especially in heavily
infested soils. To guarantee marigolds' nematode power, grow a dense stand of
the plants and allow them to flower. Then, till the plants right into the
soil. Before growing other crops in that same bed, wait at least 60 days.

For best results, keep the roots of the marigolds close to the vulnerable
garden plants. They can protect their neighboring bedmates.

If the results look encouraging, this will give growers a nonchemical tool in
controlling nematode-infested fields.

Then from the North Carolina Dept of Agronomy (1995):

Root-knot Nematodes:  Biocontrol with French Marigold

Root-knot nematodes (Meloidogyne spp.) can be effectively managed in home
gardens without pesticides. One alternative to using nematicides is to
intercrop and rotate vegetables with French marigold (Tagetes patula). The
roots of this attractive flowering plant contain chemicals that kill
nematodes. As a method of biocontrol, French marigold culture is not only
pleasing to the eye but economical and environmentally sound as well. One
drawback, however, is that the benefits are not realized until the following
year. Also, the treatment frequently needs to be repeated with marigolds and
vegetables grown in alternate years. 

Be informed when selecting marigolds for use against nematodes. Marigolds sold
as bedding plants may be hybrids or species other than Tagetes patula. Studies
indicate that many T. patula varieties are effective in reducing the most
common root-knot nematode populations, Meloidogyne incognita and M. javanica.
Varieties proven to be effective, such as 'Tangerine,' 'Petite Harmony' and
'Petite Gold,' are no longer widely available. However, all of the currently
available varieties in the 'Hero,' 'Safari,' 'Disco,' 'Bounty' and 'Little
Janie' series are true French marigolds and are expected to have similar
beneficial effects in the garden. 

Then the Ag Ext of Fort Valley University,Fort Valley, Georgia 
(ummmm who?- smirking remark by this author with upfront apologies to all Georgians)

Plant marigolds…  Another approach is to devote one section of the garden to
growing marigolds. Companion planting or spot planting of marigolds in the
garden site will not control nematodes. A given area must be planted solid
with marigolds. Any other root system in the area may support root-knot
nematode populations. The marigold crop should be in the soil in the ground at
least 90 days. 

So, starting to get the drift here? Lots of anecdotal comments, some research
and no difinitive answers (at least that I found). But it appears the the
roots do the job and good gardening pracices help a lot. Then of course there
is solarization....

Had enough??? do I hear Uncle????    :>)))

John                     | "There be dragons here"
                         |  Annotation used by ancient cartographers
                         |  to indicate the edge of the known world.

USDA zone 8/9 (coastal, bay) 
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