S-Ethyl dipropylthiocarbamate (EPTC) is a soil-applied herbicide registered for use in many specialty crops and provides limited weed control applied alone. However, the lipid synthesis inhibitor mode of action of EPTC may improve POST-applied herbicide efficacy by altering cuticle formation. Studies were performed in 2014, 2015, and 2016 to assess whether EPTC applied PRE or POST increased POST-applied herbicide efficacy. Treatments were arranged as a randomized complete block design with three replications. EPTC at 3,360 or 4,480 g ha⁻¹ or ethofumesate at 280 or 560 g ha⁻¹ were applied pre-plant incorporated in late May 2014 followed by bentazon at 70 g ha⁻¹, halosulfuron-methyl at 35 g ha⁻¹, or fomesafen at 210 g ha⁻¹ applied POST to 5- to 8-cm weeds in late June. EPTC was applied in late May 2015 at 980, 1,960, and 2,940 g ha⁻¹ followed by bentazon, halosulfuron-methyl, or fomesafen as previously described. EPTC was applied POST at 980, 1,960, 2,940 g ha⁻¹ in combination with or 7 days prior to bentazon, halosulfuron-methyl, or fomesafen as previously described in May 2016. Visible injury to redroot pigweed (Amaranthus retroflexus L.), lambsquarters (Chenopodium album L.), and common ragweed (Ambrosia artemisiifolia L.) was evaluated 14 and 28 days after treatment (DAT). EPTC applied PRE at labeled field rates increased the efficacy of all POST herbicides to greater than 90 % control 14 and 28 DAT on all weeds. The benefit of EPTC was more apparent at 28 DAT when the control remained higher compared with POST herbicides alone. The rate of EPTC should be greater than 1960 g ha⁻¹ to achieve an acceptable level (80–100 %) of weed control. EPTC applied POST 7 days prior to or tank-mixed with POST herbicides increased weed control approximately 10 % regardless of POST herbicide.