Quantifying pesticide overuse from farmer and societal points of view: An application to Thailand

• Pesticide overuse is quantified from a damage control function and pesticide costs.
• By including externalities we determine social pesticide overuse.
• We apply the method to intensive Thai horticulture using farm- and plot-level data.
• We find that 79–80% of the applied pesticide amount is in excess of social optima.
• The findings suggest that a tax as stand-alone intervention might be ineffective.

The rapid growth in pesticide use is a significant problem for Thailand, as it is in many other developing countries with an intensifying agriculture. The objective of this study was to quantify how much of the total quantity of pesticides is overused. The novelty of this research resides in the fact that it considered the social rather than the private optimum by including negative pesticide externalities in determining levels of overuse. Marginal benefits of pesticides are quantified by estimating Cobb–Douglas production functions with an exponential damage control specification. The marginal costs are calculated as the sum of private and external costs with the latter quantified using the Pesticide Environmental Accounting (PEA) tool. The method is applied using farm- and plot-level data from one intensive upland vegetable production system in northern Thailand. The findings show that about 80% of the applied pesticide quantity is used in excess of the social optimum, while the difference between the private and social level of overuse is small for this particular case study. Therefore results from the study area suggest that internalizing pesticide externalities into the price of pesticides would only have a small effect on reducing pesticide overuse.