Insecticides: Agricultural chemicals, article 3 of 3

Insecticides are agricultural chemicals used in pest management in crops. In

Kenya the insecticides bear different trade names that are popular among

farmers and the agro-dealer shops outlets. These names are given to have a

good appearance and appeal to the farmers. For each product however there is

what is referred to as the active ingredient. This is the specific molecule that

is contained in the product. This means that we can have many different

products bearing different names but will have the same active

To understand the insecticides and their work well we have to know what they

target. Insect pests are majorly divided into two broad categories; piercing and

sucking pests (aphids, thrip, whitefly, mealy bug, scales, spider mites-Acari) &

biting and chewing pests (caterpillar-Lepidoptera). This is a description based

on the type of feeding and damage each causes. For this reason we have

insecticides targeting each category. We also have insecticides that we call

broad spectrum; meaning they are able to target both categories.

Apart from these, the insecticides also bear another feature referred to as

mode of action. This is how the insecticide works when sprayed to a crop. First

we have contact insecticide; these will only be active on the specific part of the

plant that they have been sprayed on. For this type of insecticide coverage on

spraying should be intense to ensure all parts of a plant are sprayed. The second

type is referred to as systemic. This means if sprayed on one part of the plant,

it is able to spread to other parts of the plant through the plant system. Some

insecticides may be locally systemic, meaning they are able to spread to the

adjacent parts of the places they have been sprayed on. Others bear a feature

called “translaminar effect” which means that they are able to penetrate from

the upper part of the leaf to the lower part of the leaf and vice versa.

Residual refers to the number of days that the specific insecticide will remain

active in the plant. These have different day; some 7, others 14 and others 21

days. Post harvest interval (PHI) refers to the number of days after which the

sprayed crop is safe and fit for consumption. After these days the chemical

sprayed will not have any effect to the consumer; but may still have an effect

to the target pest. It is always healthy and safe to observe PHI days.

Every farmer should only apply the recommended rates of any given insecticide.

Safety precautions should be also observed during the spraying. After this the

chemicals should be well stored in a cool and dry place; away from any

unauthorised access. A farmer should always seek advice from crop protection

specialists on the best insecticides to use and the best way to use them in order