Toxicity of Soil-Incorporated Trifluralin to Johnsongrass (Sorghum halepense) Rhizomes

Rhizomes of johnsongrass [Sorghum halepense (L.) Pers.], cut into 2.5-cm or 15-cm lengths, were planted in the field within and below a 7.5-cm layer of soil mixed with trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0, 1.7, or 3.4 kg/ha. When planted 3.8- and 10-cm deep in nontreated soil, survival was 90% and 69%, respectively, for the longer rhizomes and only 39% and 10%, respectively, for the shorter ones. When planted within trifluralin-treated soil, 95% and 100% of the shorter rhizomes and 54% and 81% of the longer rhizomes were killed at 1.7 and 3.4 kg/ha, respectively. When planted below treated soil, only 11% or 19% of the longer rhizomes were killed. The shorter rhizomes planted below the treated soil survived at less than 10%.