Into the Weeds: A Structural Model of Herbicide Demand and Glyphosate Resistance on U.S. Corn Farms
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The first case of glyphosate resistant weeds was documented in 1998, two years after the
commercialization of genetically engineered, herbicide tolerant (HT) corn and soybeans.
Currently, over 14 resistant weed species affect U.S. crop production areas. This study uses
a novel two-stage, structural model to derive cost functions for pre-emergent and postemergent
herbicide use. The parameters of the structural model are estimated using
censored nonlinear full information maximum likelihood. Control functions from firststage
regressions account for endogeneity of farmers’ profit-maximizing decisions. The
results of the analysis are used to determine the extent to which resistance has eroded the
benefits associated with glyphosate applications in HT production systems. Our
preliminary results suggest that glyphosate resistance may have decreased weed control by
as much as 11 percentage points from 2005 to 2010.