Agriculture Reference
In-Depth Information
Nematicides
Action of fungicides
No active ingredients are at present available to
gardeners for nematode control.
Fungicides must act against the disease but not
seriously interfere with plant activity. Fungicides may
act either in a
protectant
way on the plant surface, or
in a
systemic
way inside the plant.
Fungicides
Benefits and limitations of fungicidal control: see
general points for chemical control on p. 199.
Safe practice and environmental impact of fungicidal
control: fungicides used in gardening do not represent
the danger of human and environmental toxicity that
may be found in insecticides.
X
However, care needs to be taken when mixing
and applying fungicides. The
concentrated
trade
product represents a particular risk. Products for
gardeners are chosen for their low level of toxicity
to humans (see toxicity aspects of pesticides, p.
200), but gardeners still need to be careful.
Natural balances:
X
While the fungicide ingredients available to the
private gardener do not have a high toxicity to
benefi cial animals that is seen with the insecticides
and acaricides, it should be remembered that fungi
are found throughout gardens, helping to break
down dead plant material to form humus. There
are also many fungi acting in
benefi cial
ways, as
biological control agents of pests, against disease-
causing fungi on the leaf surface (phyllosphere),
around roots (rhizosphere) and in composting (see
pp. 158-161).
X
Disease controls with broad-spectrum ingredients
such as copper, or systemic chemicals such as
myclobutanil
may reduce the levels of these
useful fungi, but strong evidence to support this
claim is not yet available.
Restoring natural balances:
X
Provide plants with optimal conditions of soil
fertility (see p. 140) and microclimate that will
reduce the likelihood of fungal (and bacterial)
infections, but will encourage benefi cial bacterial
activity.
X
Provide plants (particularly seedlings) with disease-
free soil and composts. Avoid the introduction of
infected plants (see p. 194).
X
Choose cultivars with a proven record of
plant
resistance
where possible (see p. 205).
X
Read the pesticide product
label
carefully to
check whether the chosen active ingredient kills
biological control and pollinating species. Internet
sources will give more detailed information.
X
Be particularly careful when spraying in
glasshouses using introduced
biological control
species
, or near
ponds
.
Examples of fungicide active ingredients
X
Inorganic chemicals
contain no carbon. Two
chemicals are available to gardeners. Copper salts
mixed with slaked lime (
Bordeaux mixture
) form a
microscopically thin protective barrier to fungi such
as potato blight when sprayed on the leaf. Another
copper formulation (
Cheshunt mixture
) has a
more 'tender' action on young roots of seedlings
and young plants while controlling damping-off
disease. Fine-grained (colloidal)
sulphur
, applied as
a spray, controls powdery mildews and apple scab.
X
Myclobutanil
belongs to the conazole group. It
is protectant and systemic, on powdery mildews,
black spot of rose and apple scab.
Formulations
Active ingredients are mixed with other ingredients to
increase the efficiency and ease of application, prolong
the period of effectiveness, or reduce the damaging
effects on plants and humans. The whole product
(
formulation
) in its bottle or packet is given a trade
name, which often differs from the name of the active
ingredient. The main formulations are liquids, wettable
powders, dusts and baits.
Plant damage
The commonest damage is from herbicide sprays.
Care should be taken not to spray in windy weather
or to spray too close to garden plants. Insecticides
and fungicide sprays may harm plants, particularly
in
hot weather
when the leaves may be scorched.
Plants growing in
greenhouses
are more susceptible
because their leaf cuticle is thinner than that of plants
growing at cooler temperatures. Careful examination
of the pesticide (particularly herbicide) packet
label
often prevents this form of damage occurring.
Product label
The 'statutory area' on the label present on each
packet or bottle of pesticide must provide the
following details:
X
The fact that the product is for garden use.
X
The plant species, crop or situation where
treatment is permitted and the maximum dose or
concentration.
