Use of pesticides and fertilizers on farms and in other places has increased by a lot over the past 50 years, fueling increases in crop production globally.
But there have been serious environmental consequences. Indiscriminate pesticide and fertilizer application may pollute nearby land and water, and chemicals may wash into nearby streams, waterways. Pesticides can kill non-target organisms, including beneficial insects, bacteria and fish. Fertilizers are not directly toxic, but their presence can alter the nutrient system in freshwater and marine areas. This alteration can result in an explosive growth of algae due to excess nutrients, as nitrogen, phosphorus and sulfur.
As a result, the water is depleted of dissolved oxygen, and fish and other aquatic life may be killed. This phenomenon is called eutrophication:
https://it.wikipedia.org/wiki/Eutrofizzazione
Are there better ways instead of which to use the pesticides ???

Impact on the environmental:
Reduction of biodiversity and so many other things... 
For example an emblematic case ( bees) 
http://www.legambiente.it/sites/default … i_2015.pdf