Discuss the advantages and disadvantages of use of herbicides to replace hand weeding. What will ...

The principal advantage is that the person who had been weeding no longer has to
do that job. As one who has hand weeded, I can attest to a sore back afterwards. Another
advantage is the amount of time committed to clear the weeds, clearly less than with hand
weeding.
The disadvantages are many. Herbicides can adversely affect the plant you are growing as a
cash crop, though less than that of the target species. They often adversely affect the health
of the person who applies them. Herbicides applied aerially can drift from the farm field to
nearby fields. Even herbicides that do not drift through the air on application may evaporate
and spread that way. The plants killed outside the target area may be essential to supply
nutrients to local insect and animal species. Local bodies of water may be adversely affected,
as can the humans who drink the water. The type of soil, the humidity, and the prospect (or
lack of prospect) of precipitation are all important.
In many cases, farmers are planting herbicide-resistant crop varieties. According to S. Z.
Knezevic and K. G. Cassman (Use of Herbicide-Tolerant Crops as a Component of an
Integrated Weed Management Program, Crop Manage., 17 March 2003,
doi:10.1094/CM-2003-0317-01-MG.), disadvantages include (A) yield performance, (B)
single selection pressure and weed resistance, (C) shifts in weed species, (D) gene escape,
(E) gene flow and contamination of organic crops, (F) drift and non-target movement, and
(G) marketing and food labeling in global markets.