What are the problems of using herbicides?

Herbicides kill plants and insecticides kill insects. Sometimes they kill other things such as animals and fish as well.

As they travel downstream they may harm wildlife and wild animals. If they get into the water supply used by humans they could be poisoned too.

We rely on the balance of nature for many predators to be killed off. Many insects naturally prey on other insects. If an insect that damages plants does not have its numbers limited by the insect that preys on it it will carry our more damage than usual and may do more damage than the plants can recover from. Once the balance of nature is lost it is difficult to exactly work out what the consequences might be.