Toluidine and Thiocarbamate Toxicity to Johnsongrass Rhizomes

The toxicity of several toluidine and thiocarbamate herbicides to johnsongrass [Sorghum halepense (L.) Pers.] rhizome tissue was determined by a triphenyl tetrazolium chloride (TTC) assay. Rhizome sections were incubated in herbicide solutions for 24 hr and then in TTC solution for 24 hr. The amount of reduced TTC was a quantitative measure of herbicide toxicity. Concentrations of the different herbicides required to cause 100% tissue injury indicated that the order of decreasing herbicide toxicity was: USB-3584 ( N 3 , N 3 -diethyl-2,4-dinitro-6-trifluoromethyl-1,3-phenylendiamine); trifluralin (α,α,α-trifluoro-2,6-dinitro- N,N -dipropyl- p -toluidine); benefin ( N -butyl- N -ethyl-α,α,α-trifluoro-2-6-dinitro- p -toluidine); nitralin [4-(methylsulfonyl)-2,6-dinitro- N,N -dipropylaniline]; San-9789 [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro- m -tolyl)-3(2H)-pyridazione]; and A-820 ( Nsec -butyl-4- tert -butyl-2,6-dinitroaniline). In another study CGA-11607 ( N -ethyl- N -tetrahydrofurfuryl-4-trifluoromethyl-2,6-dinitroaniline); AN-5647 [ N,N -bis(2-chloroethyl)-2,6-dinitro- p -toluidine]; and CGA-10832 ( Nn -propyl- N -cyclopropylmethyl-4-trifluoromethyl-2,6-dinitroaniline) were less toxic than trifluralin to johnsongrass rhizomes. Complete tissue injury caused by the thiocarbamates occurred in the same concentration range (10 −3 to 10 −2 M) as the toluidine herbicides. At a concentration required for complete kill the toxicity in decreasing order was: EPTC ( S -ethyl dipropylthiocarbamate); vernolate ( S -propyl dipropylthiocarbamate); butylate ( S -ethyl diisobutylthiocarbamate); and pebulate ( S -propyl butylethylthiocarbamate). R-25788 ( N,N -diallyl-2,2-dichloroacetamide) at 6.7 × 10 −5 M had no effect on vernolate, EPTC, or pebulate activity; but it increased the toxicity of butylate to johnsongrass rhizome tissue.