Let's talk about types of herbicide. Herbicides are chemicals used for killing weeds. Weeds are unwanted plants.
Herbicides can be classified according to:
1) when they are applied
2) how they kill plants.
3) the type of plants they killed.
So based on this herbicides can be:
1) pre-emergence or post-emergence herbides
2) contact or systemic herbicide
3) selective or non selective herbicides.
So, pre-emergence herbicides are applied before your planted crops emerge or grow out from the soil. This can be used for maize. When maize are planted, these herbicides are used a day after planting
Post emergence are used anytime after the emergence of crops. They are usually selective and are used to kill weeds around our crops. Example is 2-4-D amine.
Contact herbicides kill weeds by acting on their outer surfaces. The disadvantage is if rain falls not long after it has been applied, there won't be any effect.
Systemic herbicides kill weeds by acting on their system; vascular tissues up to their roots, and kills the weed inside out. Examples are herbicides with active ingredient of glyphosate.
Selective herbicides selects the plants to kill, there are ones that kill only broad leaf plants such as beans or cowpea and have no effect on elongated leaf plants such as maize and rice. There are some that kill elongated leaf plants and have no effect on broad leaf plants. An example of selective herbicide is 24D amine. It kills broad leaf weeds and therefore used for controlling weeds in maize farm
Non-selective kills all plants
The picture below is an example of non-selective systemic herbidicide with an active ingredient of glyphosate.
The picture below is 2-4 D amine; a selective post emergence herbicide
he is a seasoned educationist. He obtained his bachelor degree from Obafemi Awolowo University. He has written many educational articles on different blogs