I develop a mechanism in which farmers can respond rationally to heat stress and still fail to offset yield losses. The mechanism is biological timing: the phenological phase associated with the pest-related signal guiding pesticide adjustment can differ from the phase in which heat most strongly affects yield. When these signals are misaligned, defensive expenditure may be imperfectly targeted to the yield-critical threat, a pattern I term structural maladaptation. Across four major crops in Quebec over 1991–2022, yield falls significantly with heat exposure, while estimated unit-cost responses are positive for all four crops and statistically significant for oats, barley, and soybeans. The strongest evidence comes from barley, the only crop for which the retained pesticide-response and yield-critical phases differ. For barley, the interaction between yield-critical heat and pesticide expenditure is negative and precisely estimated: as sowing-phase heat rises, the conditional pesticide–yield association becomes less favorable. For oats and corn, the corresponding interactions are statistically indistinguishable from zero, while soybeans exhibit a positive interaction; all three are phase-aligned crops. A falsification exercise further shows that the barley interaction is not statistically distinguishable from zero when indexed to growing-phase heat. These results provide evidence that biological timing can constrain agricultural adaptation and motivate greater attention to phase-specific information and agronomic decision support rather than input expansion alone.

In Quebec, organic-certification exits remained persistently high at 5–7% annually over 2021–2025, while entries fell sharply from 10.8% to 3.4%. By 2025, exits exceeded entries for the first time, contracting the certified stock and reversing a decade of expansion. Using enterprise-level data spanning all product categories, we document three life-cycle exit patterns: the exit hazard follows an inverted-U shape, peaking around the third year; more than 50% of exits occur within five years of certification; and enterprises certified in more product categories face lower exit risk. A calibrated dynamic model with heterogeneous time preferences and idiosyncratic pest shocks reproduces the hump-shaped hazard through the differential exit of impatient versus patient producers. Policy counterfactuals indicate that an 80% pesticide tax raises ten-year survival from 81.0% to 89.3%, while a 1% productivity penalty in organic production lowers it to 71.8%. Long-term retention is shaped by behavioural heterogeneity in time preferences and exposure to ecological (pest) risk.

Governments overwhelmingly fight pesticide overuse with information-based instruments (national plans, quantitative targets, and integrated pest management, or IPM) and only rarely with taxes. Using a new, hand-validated database of all four instruments for 45 OECD and major agricultural economies (1990–2023), we show that the apparent success of the soft instruments is largely an artifact of selection. IPM, the most widely adopted pesticide policy in the world, carries the largest raw effect of any instrument, yet that effect collapses to zero once country-specific trends are allowed: adopters were already on declining pesticide paths before they adopted. Plans and quantitative targets have precisely-estimated null effects on the volume applied. Only the rarely-used tax shows a robust negative effect, though, resting on four adopters, its magnitude is suggestive. A circularity-free consumption footprint and a bilateral sourcing test find no large trade leakage. The robust lesson concerns instrument class: information-based policies do not measurably cut use, and their evaluation must confront endogenous adoption.

We develop a computable general equilibrium model of Quebec agriculture distinguishing conventional and organic production. Using CECPA farm-level data, we estimate a partial pesticide demand elasticity of −0.83; general-equilibrium adjustments attenuate this to −0.44, so a 28% pesticide tax is required to reach the 12% reduction target of Quebec's Plan d'agriculture durable. Revenue recycling leaves aggregate pesticide use unchanged but reshapes the structural transition: organic acreage expands by 15.1% when revenues fund organic farmers, against 1.8% under government retention and 1.0% under household transfers. The recycling rule, not the tax rate, is the primary lever of agricultural transformation.

Mandatory agronomic prescriptions insert a licensed intermediary into the pesticide purchase decision, but their causal effect on farm-level demand is unknown. We exploit Quebec's 2018 prescription requirement as a natural experiment and find that the reform reallocated pesticide demand across active ingredients rather than reducing it in aggregate. Using annual compound-level data spanning 1992–2022 and combining difference-in-differences, slope-break, and synthetic control methods, we document three patterns. The prescription accelerated the exit of atrazine at roughly 39% per year faster than its pre-policy trend; it had no statistically detectable aggregate effect on neonicotinoids, the primary public target of the reform; and sales of diamide insecticides, an unregulated substitute class, rose sharply relative to controls. The substitution roughly offsets the gain from atrazine's accelerated exit, so the prescription's identifiable causal effect on within-panel risk-weighted aggregates is approximately zero.