Differential Selectivity of Herbicides on Six Setaria Taxa

Abstract

Differential selectivity was shown for 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 2-chloro-4, 6-bis(isopropylamino)-s-triazine (propazine), and S-ethyl diisobutylthiocarbamate (butylate) on giant foxtail (Setaria faberi Herrm.) yellow foxtail (Setaria glauca (L.) Beauv.), giant green foxtail (Setaria viridis var. major (Gaud.) Posp.), robust white foxtail (Setaria viridis var. robusta-alba Schreiber), and robust purple foxtail (Setaria viridis var. robusta-purpurea Schreiber). The differentials obtained could explain the reports of uncontrolled Setaria species and the apparent increase of the latter three varieties. The two new varieties of green foxtail, robust white and robust purple foxtails, were the most tolerant varieties or species to atrazine and propazine with giant green foxtail intermediate between the robust foxtails and green, giant, and yellow foxtail. The ED50 values for the robust foxtails were also higher than for the other varieties and species studied. Yellow foxtail was the most tolerant to butylate. The effective rate, measured as percent of control, was directly related to soil organic matter content.