The use of the WISDEM model in the simulation of weed shifts in glyphosate-tolerant cropping systems

WISDEM (Weed Interference and Simple Demographic Model) is a decision-aid model developed initially by Wiles et al. (1996) and recently augmented in response to some major theoretical work by Canner, Wiles, and McMaster (2002). This model has been significantly upgraded by the present author and is presented as an ecologically-based approach to the simulation of weed shifts as well as a realistic decision-aid management tool for glyphosate-tolerant cropping systems, specifically for selecting optimal weed management products and optimal application timings. WISDEM represents each crop rotation as a controlled sequence of scheduled plant disturbance events whose timing and intensity can be varied. Crop emergence is represented as a singular pulse event, while emergence for each weed species is depicted via an empirically derived Weibull curve. Population dynamics for each plant species are calculated via a set of proportional yield equations that estimate seed production per unit area for each plant species. These equations assess the competitive influence of each cohort of each plant species according to the species' relative competitive index, degree of competitive asymmetry, and emergence timing.;In the context of the present work two algorithmic upgrades have been implemented, one which imposes a reduction in per-plant fecundity for late-emerging weed species and the other defining an effective weed density for crop yield reduction by averaging the weed densities for each species over the crop's competitive period. In addition, the curves defining the emergence timing of each weed species are re-parameterized. Sensitivity analyses are performed along with validation studies that suggest a significant improvement in WISDEM's ability to represent realistic dynamics.;Lastly, two modeling experiments are performed on the field study from which validation comparisons have taken place. In each case various model runs are performed in an effort to find an option that is economically optimal. One experiment seeks to find a suitable burn-down herbicide replacement for a pre-plant tillage event. The other experiment seeks to find optimal timings for the applications of Roundup Ultra™. In both instances the WISDEM model provides realistic recommendations that confirm its usability as a decision-aid tool.