Insect pests and plant pathogens are a challenge for every farmer and the temptation to wipe them out is strong. It is tempting to always reach for chemicals. In the short-term, chemicals may provide a quick knock-down to the attackers, but they may also kill beneficial organisms.
In the long-term, you expose yourself and the environment to toxic chemicals, and risk disrupting the natural ecosystem in your garden. Pest and disease occur mainly due to wrong cultivation practices.