Economic Threshold Theory and Decision Models for Integrated Weed Management in Nigerian Smallholder Cereal Systems

This study develops original economic threshold theory and decision models for integrated weed management in Nigerian smallholder cereal systems, providing a theoretically rigorous and practically applicable framework for weed management decision-making in the Nigerian agronomic context. Economic threshold theory, which determines the weed density at which control intervention becomes economically justified, is well-established in developed country agriculture but has not been rigorously developed for the distinctive characteristics of Nigerian smallholder systems, where labour costs, input market imperfections, risk aversion, and subsistence orientation create fundamentally different decision environments. This study extends classical economic threshold theory by incorporating risk aversion preferences, seasonal labour market imperfections, and multi-season weed seed bank dynamics into a dynamic threshold model. Weed yield loss functions are estimated from controlled infestations of Striga, Digitaria, and Chromolaena at representative population densities in maize and sorghum at sites in Kogi, Kano, and Enugu States. Stochastic threshold values are computed under assumed distributions of crop prices and control costs. Weed management decision models are validated by comparing model recommendations against farmer decisions in a three-season observational study with 80 farmers. Findings reveal that economically optimal thresholds for Nigerian smallholders are significantly lower than those applicable in mechanised high-input systems due to lower opportunity cost of labour, high crop price variability, and strong yield risk aversion. The observed threshold behaviour of Nigerian farmers is more consistent with risk-adjusted than with profit-maximising threshold models. The study contributes an original risk-adjusted weed management threshold framework for Nigeria and recommends its integration into farmer decision support tools.

Keywords: economic threshold, integrated weed management, Nigerian smallholder, decision models, weed seed bank.