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September 28, 2020

Agritours

Agribusiness in one place

Safe use of agricultural chemicals; Herbicides, Article 2 of 3

3 min read

Herbicides 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

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