Understanding factors that affect dislodgeable foliar residues of pyrimethanil and their dissipation: How relevant is...

Pesticide dislodgeable foliar residues (DFR) and their dissipation half-time (DT₅₀) after application are important parameters for exposure and risk assessment from intended reentry activities or unintended dermal contact with treated crops. To understand the impact of agronomic factors on residue level a statistical based evaluation was conducted using ten DFR studies, with pyrimethanil applied in Scala^® to strawberries, raspberries, peppers, apples, and grapes, 30 trials in total. Influences on initial DFR (DFR0) and DT₅₀ were investigated by multivariate linear regression analysis. The application rate and the crop itself indicate a potential influence on DFR0 when related to ground area applied which is not notable for three dimensional crops regardless of indoor/outdoor cultivation, when related to leaf wall area (LWA). DFR0 values for pyrimethanil do not depend on the number of applications as the range of DT₅₀ values determined for pyrimethanil is consistently small (0.3-2.3 days). All DT₅₀ are significantly lower than the European default (30 days). The noted difference in DT50 of peppers to strawberries is likely attributable to indoor cultivation. A proposal is made how to refine the exposure assessment of pyrimethanil making use of the available DFR0 and DT₅₀ data for other crop types.