Michael McCallum

Abstract

Glyphosate-based herbicides are widely used in modern agriculture. Their broad-spectrum efficacy as non-selective systemic herbicides, combined with the expiration of their patent in 2000, has made them a highly cost-effective tool across diverse agronomic contexts. However, their extensive use has generated increasing environmental and regulatory scrutiny. Since their incorporation into modern cropping systems, farmers have often expressed reluctance to accept restrictions on their use, reflecting an ongoing debate in which advocates emphasize glyphosate’s role in facilitating conservation practices, while critics highlight potential toxicological and ecological risks. Rather than seeking to resolve this debate, this thesis provides empirical evidence on the pathways leading to varying levels of glyphosate use by analyzing commercial arable and mixed farming systems from the DEPHY network over an eleven-year period.

A multi-phase analytical framework combining descriptive statistics, regression modeling, machine learning, and causal inference was applied to examine glyphosate use across three complementary dimensions: patterns of mobilization, cropping system archetypes associated with contrasting use pathways, and economic implications. Plowing emerged as the clearest factor associated with a reduced likelihood of glyphosate use. More broadly, glyphosate appears to function less as an agronomic necessity than as an operational buffer used to streamline workflows, provide temporal flexibility, and mitigate the risk of insufficient weed control. Crop diversification may reduce the intensity of GBH use, but does not necessarily eliminate reliance on them. When production contexts are comparable, no detectable differences were observed in gross product, gross margin, operating or equipment costs, or total workload, between users and non-users of GBH. By identifying structural pathways associated with glyphosate use, this research highlights the importance of cropping system redesign, advisory support, and policy frameworks in enabling feasible transitions toward more sustainable agricultural systems.

 Jury:

• Pr. Guillemin, Jean-Philippe - Président
• Pr. Médiène, Safia - Rapporteuse
• Dr. Thiollet-Scholtus, Marie - Rapporteuse
• Dr. Lamichhane, Jay-Ram - Examinateur
• Pr. Peigné, Joséphine - Examinatrice
• Dr. Chauvel, Bruno - Examinateur