Controlling Aphids
Compared with other insects, aphids are relatively easy to control. With light
infestations on small areas the plants can be sprayed vigorously with a soap and water
solution, or even water alone. This knocks the aphids to the ground; normally they do
not climb back onto the plants, and the soap acts as a deterrent to further attack.
With more severe infestations of aphids, mild non-persistent insecticides such as
derris (a climbing leguminous plant Derris elliptica from SE Asia that contains rotenone
in its roots) and pyrethrum (Chrysanthemum cineralifolium) give good and safe control.
Aphids very often congregate together at the tips of plants such as broad (horse)
beans. If the plants are big and strong enough the infested tips can be removed by hand,
then destroyed.
Preventing Aphids
On a small, garden scale a repellent can be made by boiling in water the leaves and
stems of plants such as rhubarb, anise, chrysanthemums, coriander, asters and
marigolds, or mixtures of these plants. A strong solution of this sprayed onto plants acts
as a fairly reliable deterrent. Soap and water sprays can also work.
Insecticides
Most modern insecticides, or pesticides, are synthetic organic compounds such as
chlorinated hydrocarbons, organo-phosphorus compounds and carbamates. They are
available in either granular, liquid or powder (dust) form.
Systemic Insecticides
These work by being absorbed by plants, remaining within the plant tissues. They are
used to control sap-feeding insects such as aphids and capsids. Many of them also kill
by contact and give protection for a week or so in this way, until the active chemical is
absorbed within the plant.
Contact Insecticides
These rely on coming into physical contact with the insects.
The third group of insecticides, which includes gamma-BHC and Malathion, are
essentially contact insecticides but also have some systemic action.
Online information is available from the Pesticide Action Network website.
Even under rigidly controlled safety conditions insecticides are highly toxic chemicals
which can cause suffering and death to fish, insects—beneficial as well as harmful—
livestock, wild animals and people. If it is absolutely necessary to use insecticides then
the greatest care must be taken to observe all safety precautions, which are normally
clearly described on the chemical container. In Sri Lanka, and elsewhere, one of the
commonest causes of farmer death is from pesticide poisoning.
In Europe, the mandatory Pesticide Safety Precautions Scheme (PSPS) and
registration scheme ostensibly minimises hazards.
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)Insecticides are Deadly!