Safe use of agricultural chemicals; Herbicides, Article 2 of 3
3 min readHerbicides are agricultural chemicals that are used to control unwanted/undesired
plants/vegetation in the field. These unwanted plants are what we refer to as
weeds. In other instances herbicides may be called weed killers. They interfere
with the growth of the target crop. They may be applied in the soil or sprayed in
the leaves/foliage. This can be done at different times. Pre-plant means
herbicide application before planting. Pre-emergence application means
application before weed seedlings emerge through the soil surface. Post-
emergence application is done after weed seedlings have emerged through the
Herbicides are broadly divided into two categories; selective herbicides and
non-selective herbicides. The selective herbicides only destroy selected plants
leaving the desired crop intact. A good example is the 2, 4-D herbicide used in a
maize field; this destroys all other crops except the maize. Selective herbicides
are available for other wide varieties of crops like bean, onion, carrot, tomato,
wheat, among many others. On the other hand, non selective herbicides are used
to destroy any existing vegetation that comes into contact with it. This is a
great tool used for land preparation during land preparation. It is worth noting
that non-selective herbicides are also used in other industries like construction
to help completely eliminate any vegetation on site.
There have been debates on whether herbicides really destroy/degrade the
soil. For us to establish the correct answer we should know how herbicides work;
residual effect, means of uptake and the mode of action. First we should know
on the residual effect, which tells us how long the chemical remains active in
the sprayed crop or soil. Some will take just a few hours while other may take
several days to become inactive. Some herbicides will be absorbed through the
leaves while others are taken through the roots. In the mode of action some will
be systemic while others are contact. Contact means that they will only act on
the part they come into contact with, while systemic means that regardless of
the part they come into contact with, the chemical is able to run through the
plant’s system to reach all parts of that plant. We should also note that some
herbicides will work even when sprayed on the soil. Others will not work if they
come into contact with soil; even dirty/muddy water makes them inactive, a
good chemical example is the Glphosate. So if a herbicide isn’t affected by
soil, have a long residual effect and may be taken up through the soil may
destroy/degrade the soil. If it is a selective herbicide with these qualities then
it will destroy any subsequent target crops planted in the sprayed field. The
effects that they may bring include persistence in the soil and toxicity.
The use of herbicides is greatly encouraged in the practice of conservation
agriculture. The emphasis is on minimal disturbance of the soil in order to
conserve both the soil qualities and the moisture available. Great emphasis is
put on safe use of herbicides by the farmer observing the correct application
rates as well as using the right herbicide(s) at the correct time in the crop