The lack of sufficient observed data led us to estimate crop-specific pesticide use intensity factors on the basis of expert knowledge as well as from technical guides published by various agricultural cooperatives and extension organizations. Information was gathered from interviews with a panel of 21 experts from the public agricultural research sector, extension organizations, and private companies (for further details, see the acknowledgment section at the end of this paper). Interviewees were identified as recognized national experts on crop protection for each of the crops considered. In the case of the most widely grown crops, such as small grains, several experts were identified according to pesticide category (fungicides, insecticides, etc.). The experts’ estimates correspond to the principal protection programs applied at the national level in recent years. This meant that we did not calculate crop-specific pesticide use intensity factors for each year, but average factors over several years. Each factor ∝k,t is thus constant over time. The subscript t is superfluous and can be suppressed;∝k,t is thus replaced by ∝k.This approach allowed us to define an overall index of pesticide use (NODU [LU]t) equal to the sum, for all crops, of the fixed pesticide use intensity factor specific to each crop(∝k) multiplied by the agricultural land area devoted to that crop (Sk,t), or: