Is field plankton safe to use if you have a mosquito sprayer system? The tiny frogs and toads in our yard don't seem to mind, and neither does the plankton.
not sure what kind of mosquito sprayer your talking about but most municipalities that spray for mosquitoes (i assume this is what your talking about) generally use malathion mixed with diesel fuel to spray. the pesticide degrades sufficiently within two weeks so your probably in the clear since i assume sprayings have discontinued in this colder part of the year.
i would personally be more afraid of pathogens hitching a ride on the feeders. thats not to say that i havent personally done field sweepings in the past, but i havent done it in a long time.