Agriculture Reference
In-Depth Information
(e.g. mustards) may be superior to those with longer-chain or aromatic ITCs (rapeseed)
due to higher volatility, reduced sorption of those compounds to organic matter in soil,
and the resultant maintenance of biocidal activity (Matthiessen & Kirkegaard, 2006). This
may override their often lower level of contact toxicity demonstrated in laboratory agar
assays (Matthiessen & Shackleton, 2005). The species or variety selected will preferably
grow vigorously and remain vegetative or have just commenced fl owering at the intended
time of incorporation. The best commercial biofumigants can produce >300 mol ha
-1
of ITC-liberating GSL. Ideally, the biofumigant should not host the targeted disease or
other diseases and pests of the commercial crop involved and should have a low risk of
becoming a weed.
(c) Grow and incorporate at least 5% W/W of fresh material if possible
Recent studies suggest that increasing the amount of incorporated fresh material up
to around 5% W/W improved pathogen suppression, while a diminishing response
was observed at higher rates (JA Kirkegaard, unpublished data). This is equivalent to
incorporation of 5-6 kg m
-2
of fresh vegetative biomass into the top 20 cm of soil. As far
as ITC-based suppression goes, the diminishing response at higher rates of incorporation
may result from the liberated ITC reacting with proteins and amino acids associated with
the incorporated plant material itself, rather than with the targeted disease organisms. This
may explain the lack of increased effectiveness of biofumigants at higher rates of amend-
ment such as those used for high N seed meals (Brown & Morra, 1997). Suppression
which is related to non-GSL mechanisms may improve at higher rates of amendment and
in this case the strategy would be to maximize organic matter input.
(d) Incorporation strategy - macerate-incorporate-irrigate
Pulverize the plant tissues to generate as much cellular disruption as possible prior to
incorporation to maximize ITC release. Machinery with fl ailing or crushing actions
rather than chopping can generally achieve greater ITC release (Matthiessen
et al
., 2004).
Incorporate the pulverized material rapidly into the soil with thorough mixing to distrib-
ute the ITCs. Alternatively, if soil structural preservation is a priority, or application is to
perennial vine or tree crops, watering from the top can also move the ITCs into the soil
from pulverized material or seed meals. Irrespective of incorporation method, ensure high
water availability to facilitate hydrolysis, assist to distribute ITC evenly and to assist in
reducing volatile losses from the surface.
(e) Cover the soil to reduce volatile losses
The losses of ITC from the soil surface can be reduced if the material is buried or covered
by soil during incorporation, or the soil is tapped or covered following incorporation. In
some systems (e.g. strawberries), this can coincide with the placement of the standard
plastic mulch on the beds. Opportunities to utilize integrated strategies using solariza-
tion or biological dis-infestation can potentially be combined with biofumigation using
various covering material (see Chapter 10).
(f) Allow at least 1-2 weeks prior to planting following crops
GSL hydrolysis products including ITCs can have signifi cant phytotoxic effects on plants
if suffi cient time is not allowed for the compounds to dissipate in the soil. In most cases
depending on the conditions, 2 weeks is generally suffi cient to avoid negative impacts of
persistent allelochemicals. Re-watering during the days immediately after incorporation
