Field experiments were conducted in 1977 and 1978 to determine susceptibility of rhizome johnsongrass [Sorghum halepense(L.) Pers.] to metriflufen3{2-[4-(4-trifluoromethylphenoxy) phenoxy] propanoic acid, methyl ester} applied as preplant-incorporated, preemergence, or postemergence treatments. Rates of metriflufen applied preplant incorporated and preemergence were 1.12, 2.24, and 3.36 kg/ha. Postemergence treatments consisted of 0.56, 1.12, and 1.68 kg/ha of metriflufen plus a non-ionic polyethylene glycol alkyl ester, each applied to johnsongrass at growth stages of 30 to 38 cm, 60 to 75 cm, and heading. Johnsongrass control increased with each increase in rate of soil-applied metriflufen with no differences in control between preplant incorporated and preemergence treatments. Johnsongrass density was reduced by increased rates of metriflufen, and 1978 soil-applied treatments reduced densities by 62%. Preplant-incorporated and preemergence applications of 3.36 kg/ha of metriflufen resulted in higher soybean yields than did the two lower rates. Results from treatments with trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were similar to those with metriflufen at the same rate. Metriflufen applied to 30-to 38-cm johnsongrass reduced stands by 60% in 1978, but stands increased by 51 and 71% in plots treated at the 60- to 75-cm or heading stages of growth. Soybean tolerance to postemergence applications of metriflufen was excellent for all stages of growth and rates of metriflufen.
