With biologically intensive food growing, which favors diversity and life over chemical poisons, only about 5% of the crop is lost.
Where all pesticides, biocides, and rodentcides known to human kind are used in current agricultural practices, 37% of the crop is lost. If none are used under current practices, about 42% would be lost1
Footnotes:
1) David Pimentel, Environmental Costs of the Application of Pesticides Primarily in the United States, Environment, Development and Sustainability (2005) 7: 229-252.