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USE OF METHAM SODIUM TO ELIMINATE PHYTOPHTHORA SPP. FROM
ROADING GRAVEL
E.M. Davison A , S. Kazemi B , S. McDonald C , S. Paton D , F.C.S. Tay A , B. Warton E and N. West B
A
Department of Environment and Agriculture, Curtin University, GPO Box U1987, Perth, WA 6845, Email: e.davison@curtin.edu.au
B
ChemCentre, PO Box 1250, Bentley Delivery Centre, WA 6983
C Curtin Water Quality Research Centre, Curtin University, GPO Box U1987, Perth, WA 6845
D Nufarm Australia Ltd, Lot 51, Mason Road, Kwinana, WA 6167
E Department of Applied Chemistry, Curtin University, GPO Box U1987, Perth, WA 6845, present address: ENV. Australia Pty. Ltd., PO
Box 7480 Cloisters Square, Perth WA 6850
ABSTRACT. The introduced soil-borne pathogen Phytophthora cinnamomi (the dieback fungus) can be spread to areas of
native vegetation by the movement of soil, including gravel. Gravel is widely used in Western Australia for road
construction, and many contracts for its supply specify that it must be dieback-free; however, dieback-free gravel is in short
supply. Metham sodium is a soil fumigant that has the potential to eliminate Phytophthora spp. from infested gravel. It is
currently registered for treating soil, but not for treating gravel. Our experimental work shows that it is effective at killing
Phytophthora spp. in infested gravel, and can be used safely. This is the basis of an application to the Australian Pesticides
and Veterinary Medicines Authority for a label change to allow its use for treating gravel stockpiles throughout Australia.
INTRODUCTION
About 3 000 m 3 of gravel are needed to construct a km of
rural road. MAIN ROADS Western Australia estimates that
more than 5.5 million m 3 of gravel are required annually in
WA. Gravel is cheap, costing about $4 per m 3 at the gravel
pit, but costing $9.90-$14.80 per m 3 delivered on site.
Cartage is a major cost because gravel is bulky and heavy
(1).
Phytophthora cinnamomi (the dieback fungus) is an
introduced soil-borne pathogen that is associated with the
death of native plants in the south-west of WA. It is readily
spread in infested soil, including gravel. Many contracts for
gravel supply specify that it must be dieback-free, i.e.
sourced from an uninfested site. In the past, gravel suppliers
have been able to meet this requirement; however this is
becoming increasingly difficult. Suitable gravel may be
available, but only from an infested site, so will not meet
contract specifications, or it may only be available a distance
from where it is required, resulting in high transport costs.
Metham sodium is a soil fumigant that may be suitable
to treat infested gravel. It is registered by the Australian
Pesticides and Veterinary Medicines Authority (APVMA)
and is used in intensive horticulture. When applied to moist
soil it decomposes into methyl isothiocyanate (MITC), the
active toxic compound. When metham sodium is applied to
soil, surface sealing is needed to increase the residence time
of MITC and minimise the risk of exposure to the operator.
Gravel contains a small amount of water and fines that
crust on exposure to air. This crust may be sufficient to seal
a stockpile, thus minimising MITC exposure and increasing
residence time.
Metham sodium is currently not registered for treating
gravel. We have conducted several experiments to determine
the rate of metham sodium needed to kill Phytophthora spp.
in gravel, to determine the distribution and persistence of
MITC in treated gravel, and to determine the concentration
of MITC emitted from treated stockpiles. This information
is used in an application to the APVMA for registration of
this treatment to produce dieback-free gravel.
MATERIALS AND METHODS
Efficacy Several experiments using small gravel stockpiles
were prepared on a secure experimental site. Pine plug
inoculum of either P. cinnamomi or P. cinnamomi and P.
multivora contained in small wire cages, was added during
stockpile construction. Metham sodium at the required rate
was also added during construction, ensuring that it did not
come into direct contact with the inoculum. Pine plugs were
removed at different times after treatment and plated onto
selective agar to determine the persistence of Phytophthora.
MITC concentration in gravel Small quantities of gravel
were removed from different parts of the stockpiles at
different times after treatment. MITC concentration was
determined by standard methods.
Air quality monitoring Air sampling for MITC was
conducted between 0 and 16 m from a treated stockpile for
up to 7 days.
RESULTS
Efficacy Phytophthora spp. could not be re-isolated from
pine plugs in gravel stockpiles treated with metham sodium
within the label rate for soil treatment. A representative
example of results is given in Table 1.
Table 1. Mean recovery (%) of Phytophthora spp. after
13 days in gravel treated with metham sodium. Standard
deviation is given in parenthesis.
Treatment P. cinnamomi P. multivora
Metham sodium 0 0
Control 97 (5) 89 (16)
MITC concentration in gravel MITC was well distributed
in treated stockpiles within 3 days; it was not detected after
28 days.
Air quality monitoring MITC was only detected adjacent
to the treated stockpile within 24 hr of treatment with
metham sodium.
DISCUSSION
Metham sodium is effective at killing Phytophthora spp. in
gravel. The surface crusting of gravel is sufficient to prevent
MITC escaping from treated gravel on all but the day of
application. An application has been made/is about to be
made to the APVMA for registration of this treatment.
ACKNOWLEDGEMENTS
MAIN ROADS Western Australia, MERIWA, B&J
Catalano Pty. Ltd. and Nufarm Australia Ltd. provided
financial and/or in kind support. This work was undertaken
at DAFWA’s Medina Research Station, under APVMA
Permit Number PER 7250.
REFERENCES
1. MAIN ROADS Western Australia (2008). Road building
needs.doc. www.mainroads.wa.gov.au.
7th Australasian Soilborne Diseases Symposium 14