Question

It is said that we shouldn't use weedicides because it causes pollution. But if we don't use then our crop get destroyed by the harmful pest. So what we should do at that stage.

Answer 1

Hey Bro! I think that you are in 9th class. So consult chapter 5 i.e The Fundamental Unit of Life. My Answer:
At that stage, you can sprinkle saturated $NaCl$ $solu^n$ that is common salt solution, which will cause exosmosis and ultimately 'Plasmolysis; i.e the death of weeds' cells.