Some denoise filters have an Interlaced arg (or similar) eg FFT3DFilter (spacio/temporal) and VagueDenoise (Spacial).
Also, Stickboy's jdl-interlace.avsi has JDL_UnfoldFieldsVertical, and JDL_FoldFieldsVertical (using flip arg), used to apply
spatial filters to interlaced material.
http://www.avisynth.nl/users/stickboy/