Christina,

The spray the testimony reveals a spray that is quite prone to drift.  Oil based sprays do not evaporate fast like water based sprays which leave such tiny droplets after evaporation that gravity becomes irrelevant.  This inhibits the spray from getting carried vertical and diluted to the point it is not a problem down wind.  Another critical factor is how high were the planes flying during application?  It makes a big difference if the planes were 20 feet off the canopy or 200 feet.  The spray nozzles are usually on the trailing edge of the wings out towards the tip to keep the spray off the tail surfaces.  The tip vortex from the wing smashes the spray down on the target quite effectively at low altitudes.  But, I suspect they were flying high over the canopy and in that case that tip vortex will just mix the spray droplets with the air very effectively in the vortex behind the wing tips.  Wind speed goes up dramatically with altitude.  It roughly
 doubles between five feet altitude and 50 feet altitude and keeps going up as you go higher.  The net result is spraying at high altitudes sets the situation up for spray drift.  And, with a kerosene based spray like this one those droplets could go a long way down wind I think.  I do not know what a long way is.  I have never seen data on high altitude spraying.  My gut feel is five or ten miles is within reason. Maybe farther?  A lot also depends on how stable the winds are at altitude as well as local terrain.  Gusty conditions and lots of hills will cause dispersal and dilution faster than steady wind and fairly flat land.  Time of day could even be important.  Thermal activity generally starts at 10 AM and peaks late afternoon on clear days and that also would cause dilution.

Drift is a horribly complicated topic.  Drift minimization is the reason application is usually done at the lowest altitude the pilot can fly at.  Those guys are crazy that fly those planes in my opinion.

Dick


" Any discovery made by the human mind can be explained in its essentials to the curious learner."  Professor Benjamin Schumacher talking about teaching quantum mechanics to non scientists.   "For every complex problem there is a solution which is simple, neat and wrong."  H. L. Mencken


 

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