Re: mustard as a fumigant

This is in response to Karen's question about brassicas as a soil fumigant.
Last year I set up an experiment in a commercial pea field here in SW
Washington to investigate the pest control potential of several crops
planted as overwintering covercrops.  I will say right off that my
experiment was washed down the river in 3 successive floods this spring.
Oh well - the trials and tribulations of on-farm research.  But what I did
learn was some of the literature on the subject.

Excuse the ad nausium message.  Just thought others might be interested in
the topic.  I am always collecting information for future reference and
would appreciate hearing from others who are researching or following this
topic.  This is an experiment which I hope to repeat in the near future.
Soil fumigants are expensive and in some cases being phased out.  I think
we need to seriously investigate alternatives.

Managment of the cover crop is critical to the success of pest control.
Winter cover crops are fall planted and plowed down in the spring.  Fall
planting should be timed so that the cover crop puts on enough growth
before winter, but not so much growth that flowering occurs before plow
down.  Not only is excess vegetative growth difficult to plow down, but
also, the seed can become a weed.

Winter hardy plants are likely to be the most effective for pest control
because it is the decomposition of green plant material which gives these
plants their pesticidal properties.  Correct me if I am wrong, anybody, but
I do not think that a dead plant when plowed down will produce the same
chemicals as decaying green tissue.  I have not seen any tests of this,
just my opinion.

Planting of the successive crop should not occur within 2 weeks of plow
down - otherwise the crop will likely suffer the same fate as the pests.
The mode of action of these cover crops does not appear to be very
discriminatory.  They likely affect beneficial organisms as well as
pathological ones.  I do not know if any research has measured this, but it
is my understanding.

To enhance the action of the pesticidal crop, tarping is suggested - this
will prevent the active chemicals from being volatilized.

Weed control - small seeded weeds are the most likely to be controled due
to some penetration factor.  I am sure this is related to seed coat and
uptake, but I do not have any results to quote.

Current research includes:

2 references from SARE/ACE report:

1.  1992.  Rapeseed planted as a green manure in potatoes for control of
root-knot nematode.  Control was up to 80%, yields were boosted 10-50%, and
weed biomass was reduced up to 50% - compared to standard pesticide plots,
I believe (not clearly stated in abstract). Project coordinator is Jeffrey
Stark, U. of Idaho, 208-397-4181.

2.  1992.  European fodder radish as alternative to aldicarb (soil
fumigant) in sugarbeets for cyst nematode control.  Infestation reduced
57%, yields boosted by 5 tons/A (30% greater than aldicarb-treated plots).
Radish acts as a trap crop.  Project Coordinator is David Koch, U of
Wyoming, 307-766-3242.

1994.  Weed control with green manures and cover crops - white mustard,
rapeseed, annual rye, and sudangrass - in green pea, potato and mint.
Kassim Al-Khatib, WSU Mt Vernon Research Station, 360-424-6121.  I do not
know if any results have been published yet.

Some papers:
Suppression of root-knot nematode populations with selected rapeseed
cultivars as green manure.  H. Mojtahedi, et al.  1991.  J of Nematology

Managing M. chitwoodi (Columbia root-know nematode) on potato with rapeseed
as green manure.  H. Mojtahedi, et al.  1993. The American
Phytopathological Soc. 77(1):42-46.

Cover crops for root lesion nematode (P. penetrans) suppression.  1994(?),
Oregon Hort Society, Diane Kaufman & Russ Ingham, OSU.

>          Dear Friends,
>          I recently attended one of the research stations field days
>          on Strawberries.  There seemed to be a great dependence on
>          chemical fumigants to control weeds, and kill every other
>          living creature.  It was mentioned that there is a variety
>          of mustard being used as a fumigant.  I am interested in
>          finding out what variety it is.
>          It was also suggested that there is a fairly good cropping
>          rotation in use in the New York area to control diseases and
>          pests.  I would also be interested in this information.
>          Thanks in advance.
>          Karen Ross
>          Extension Assistant/Water Quality
>          rossk@ext.missouri.edu
>          P.O. Box 1070
>          Buffalo, MO 65622

    Carol A. Miles, Ph.D.
    Washington State University
    Extension Agricultural Systems
    360 NW North Street
    Chehalis, WA   98532
    PHONE 360-740-1295   FAX 360-740-2792