INTERACTION OF GRAMINICIDES APPLIED IN COMBINATION WITH PYRITHIOBAC

Field experiments were conducted from 1992 through 1994 to determine t he effect of selected graminicides when applied in combination with py rithiobac for johnsongrass control in cotton. Quizalofop-P, clethodim, sethoxydim, and fluazifop-P were applied at rates recommended for rhi zome johnsongrass control with or without pyrithiobac at 70 g ae/ha. A t 14 DAT johnsongrass control without pyrithiobac was more than 85% fo r all graminicides all years except sethoxydim in 1993. When graminici des were applied in combination with pyrithiobac, johnsongrass control was 86% or less and was lower than when each respective graminicide w as applied alone, At 21 DAT, similar differences were apparent, Seed c otton yield, determined only one year, was not affected by reductions in johnsongrass control when either quizalofop or clethodim were used in combination with pyrithiobac. Pyrithiobac applied alone controlled johnsongrass 20 to 44% 14 DAT depending on year.