Technical Abstract: Two Italian ryegrass populations from Mississippi, Tribbett and Fratesi, were suspected to be tolerant to glyphosate. A third population from Mississippi, Elizabeth, known to be susceptible to glyphosate, was included for comparison. Plants, 10- to 15-cm-tall (3 to 6 leaves, 2 to 3 tillers), were treated with the isopropylamine salt of glyphosate at 0, 0.11, 0.21, 0.42, 0.84, 1.68, 3.36, and 6.72 kg ae/ha. GR50 (herbicide dose required to cause a 50% reduction in plant growth) values for the Tribett, Fratesi, and Elizabeth populations were 0.66, 0.66, and 0.22 kg/ha, respectively, indicating that both Tribbett and Fratesi populations were 3-fold more tolerant to glyphosate compared to the Elizabeth population. These three populations were also treated with diclofop at 0, 0.13, 0.25, 0.5, 0.75, 1, and 2 kg ai/ha when plants were 8- to 10-cm-tall (2 to 3 leaves, 2 to 3 tillers). Diclofop GR50 values for the Tribett, Fratesi, and Elizabeth populations were 0.25, 0.28, 0.21 kg/ha, respectively, indicating similar tolerance to diclofop in the three populations. Response of all three populations at two growth stages, 8- to 10-cm-tall and 15- to 20-cm-tall, to clethodim rate (0, 0.02, 0.03, 0.05, 0.06, 0.08, 0.09, and 0.13 kg ai/ha) was measured. Clethodim GR50 values for the Tribett, Fratesi, and Elizabeth populations at the small growth stages were 0.016, 0.023, 0.014 kg/ha, respectively, and at the large growth stage were 0.04, 0.034, 0.02 kg/ha, respectively. Alternative chemical control options, mesosulfuron, clethodim, nicosulfuron + rimsulfuron, glufosinate, and paraquat, are available for managing glyphosate-resistant Italian ryegrass, depending on weed growth stage and prevailing weather conditions among other factors.