Agriculture Reference
In-Depth Information
cutting the grass can lead to the grass becoming
scorched. It is equally important to remember that
any spray being blown onto neighbouring garden
plants will damage (or kill) the plants concerned.
Lawn clippings from a lawn recently sprayed with
2,4 D
should not be used as a mulch on fl ower
beds.
X
Residual herbicides
containing active ingredients
such as
difl ufenican
remain chemically stable and
active over a period of months at the soil surface or
in the soil. They are usually in a mixed formulation
containing a total translocated ingredient such
as glyphosate. These products are used for total
control, usually in situations such as gravel paths,
away from direct contact with garden plants.
Figure 16.11
Comma butterfl y. Its caterpillars feed on
nettle leaves
Slug killers (molluscicides)
Benefits and limitations of molluscicide control: see
general points for 'chemical control' on p. 199.
Safe practice and environmental impact of slug killers:
X
Metaldehyde
, while being very effective against
slugs (and snails), is reported to be be toxic to
small mammals, birds and some predatory insects
(see p. 197).
X
Ferric phosphate
is considered to be less
dangerous to garden wildlife than
copper
ingredients (that may build up in soil and affect
earthworm numbers).
X
Methiocarb
,
previously a common slug killer, is
considered by many gardeners to be unsuitable
environmentally as it is toxic to many forms of
wildlife.
Minimization of risks:
X
While slugs are undoubtedly a constant major pest,
the use of nematode parasites (see p. 230) and
barriers to slugs (see p. 229) provide alternatives to
chemical control.
X
Use of resistant cultivars, and encouragement of
predators such as hedgehogs, ducks, frogs and
ground-living beetles may considerably lessen slug
damage for private gardeners.
X
Use ingredients such as
ferric phosphate
rather
than
metaldehyde
or
methiocarb
where possible
to reduce environmental problems.
X
Place pellets inside containers that allow access to
slugs, but prevent the entry of mammals and birds
(see p. 229).
X
Grow less susceptible species or cultivars. For
example, 'Pentland Dell' potato cultivar is one of
the least affected by slugs.
Natural balances:
Britain and Ireland has a climate
that may bring damp conditions to the garden or
greenhouse may well be suffi cient to cause similar
damage to tomatoes.
Restoring and maintaining natural balances:
X
Avoid killing plants which maintain benefi cial
predators, parasites and pollinating species such as
hoverfl ies, butterfl ies (Figure 16.11) and bees.
X
Avoid spray drift onto useful and desirable plants.
Types of herbicide action
Herbicides can be classified into
three
groups
according to their action against weeds:
X
Contact herbicides
enter the leaf or stem, and
then kill the tissues of susceptible plants in the
particular area where they have entered. An
example is
diquat
used by private gardeners to
control annual weeds on waste ground.
X
Translocated herbicides
enter the leaf, stem or
roots and then move via the vascular system (see
p. 79) to reach all parts of the plant. This property
is particularly useful in controlling
perennial
weeds
with their extensive underground root systems
(e.g. dock), rhizomes (e.g. couch) or stolons (e.g.
yarrow), which are otherwise hard to reach for
control.
Glyphosate
is an example of a
total
translocated weedkiller.
X
Selective herbicides
are
able to kill the chosen
weed species through the leaf (or root), but leave
the surrounding garden plants
unaffected
. The
best example in gardening is the active ingredient
2,4-D
that is used in lawn herbicides to kill off
a range of broadleaved weeds while leaving
the grass unaffected. It should be emphasized
that a
careful reading
of the instructions on
the herbicide packet is necessary. For example,
spraying this active ingredient immediately after
