Growers have been mandated to use 10-ft maintained vegetative filter strips (VFS) on all PWG pyrethroid agricultural labels for several decades. Since the ability of VFS to trap sediment is known with greater certainty than any other performance aspect and was used for calibrating the VFSMOD model, uncertainty in predicted pyrethroid removal by VFS will be less than for other compounds due to the pyrethroid’s extreme hydrophobicity. Essentially 100% of pyrethroid being transported by runoff/erosion will be adsorbed to sediment as it leaves the treated field; consequently, the trapping efficiency of pyrethroids should be very similar to the trapping efficiency of sediment. The impact of the mandatory VFS on total loads of eroded sediment and pyrethroid entering receiving waters was modeled using VFSMOD with a 10-ft VFS linked with EFED’s PWC model across a range of 10 crop scenarios and 8 pyrethroids.  The fractions of the pyrethroid mass loading entering receiving waters after the VFS in the dissolved or absorbed states were examined. The impact of running VFSMOD with and without assuming carryover of residues in the VFS from one event to the next was also explored.  The magnitude of VFSMOD’s effect on EECs is highly scenario dependent due to weather and soil properties, resulting in a wide range of EEC and sediment load reductions.  Importantly, since some scenarios are dominated by aerial drift entry, the impact of VFS on water column EECs can be lower than expected; however, their impact on reducing sediment loading to receiving waters is vital. Moreover, VFS responses are often non-linear since they can be less effective during extreme rainfall events and therefore, their effect needs to be examined across the entire period as well as for the year corresponding to the 1-in-10 EECs since this mitigation is so important for reducing pyrethroid mass loading in all years.<br/>

Vegetative Filter Strip (VFS) modeling in risk assessment

254th National Meeting (2017)

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