Alternatives to Methyl Bromide - DTIE

3 Control of Soil-borne Pests
Soil-borne pests can cause substantial crop
damage and economic losses. This is particularly
true in intensive agriculture where crops
are planted in the same place year after year,
creating conditions that foster pest populations
in the soil.
The five main categories of soil-borne pests
are as follows:
Nematodes. Tiny worm-like creatures
that live in the soil, nematodes vary in
size from microscopic to about 5 millimetres
in length. Some species are agricultural
pests, while others are actually
advantageous to agriculture. Pest nematodes,
generally called plant parasitic
nematodes, feed in or on the roots of
crops. Root knot nematodes for example,
cause large swellings in plant roots.
These root galls drain a plant’s energy
resources and limit the uptake of water
and nutrients, thus reducing crop
growth and yields (Strand et al 1998).
Some nematodes transmit harmful viruses
or leave open wounds that allow
pathogenic fungi to enter roots.
Fungi. Certain soil-dwelling fungi (such
as species of Fusarium, Verticillium and
Phytophthora) attack plant roots or the
base of stems, causing diseases in the
plants and reducing crop yields.
Bacteria and viruses. A number of soilborne
bacteria and viruses are also
harmful (pathogenic) and cause diseases
in crops. As with nematodes and fungi,
the soil contains some beneficial bacteria
that help to protect plant health.
Soil insects. Certain soil-dwelling
insects, such as cutworms and false
wireworms, damage plants by eating
roots or infecting them with fungi or
bacteria. Some of the insects that eat or
damage plant leaves and fruit spend certain
stages of their lives in the soil, typically
as larvae or pupae.
Weeds. A range of weeds and weed
seeds cause problems by competing with
crops for root space, nutrients, water
and sunlight. These include annual and
perennial broadleaf weeds, grasses and
sedges. A few weeds, such as broomrape,
are actually parasitic on crops.
Though it is capable of controlling many
pests (see Table 3.1 through 3.5), MB is often
applied to control just one or two groups of
pests or used as general insurance against the
broad range of soil pest problems. Frequently,
farmers who use MB do not know which
pests are present in soil. Thus some MB is
applied when it is not actually necessary.
Though sometimes portrayed as the perfect
pest control tool, MB does not control all
pests. For example, MB has only limited effect
in controlling the disease caused by
Phomopsis sclerotioides in cucumber
(Gyldenkaerne et al 1997). Likewise, corms
and seeds of weeds such as horseweed, mallow
and legumes, and many bacteria are not
effectively controlled by MB (Klein 1996).
There are other disadvantages as well. MB
kills many of the soil organisms that benefit
agricultural production. It is highly toxic;
some forms of application are rather complicated;
it may leach into water in some areas;
Section 3: Control of Soli-borne Pests
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