Shields, E.J., J.T. Dauer, M.J. VanGessel, and G. Neuman. 2006. Horseweed (Conyza canadensis) seed collected in the planetary boundary layer. Weed Sci. 54:1063-1067. <BR> <BR>Altitude <BR> (ft) <BR> 230 <BR> 460<BR>Seeds found <BR>(#/1000 m3)* <BR> 3.3 <BR> 1.7<BR> * Approximately 33 by 33 by 33 ft<BR>