Greenhouse experiments were conducted in the summer of 2002 to determine the effect of root-knot nematodes on purple nutsedge suppression and chile pepper response after applications of halosulfuron. Purple nutsedge and chile pepper plants were grown together in 20-cm-diam pots, inoculated with root-knot nematodes, and treated with halosulfuron 2 or 4 wk after inoculation. Root-knot nematode infection had no effect on purple nutsedge control or chile pepper injury after treatment with halosulfuron, regardless of application timing. However, root-knot nematode reproduction was lower in pots that received a halosulfuron treatment, particularly halosulfuron applied 2 wk after inoculation. Controlling purple nutsedge using halosulfuron in a field infested with root-knot nematodes could also decrease the amount of nematode inoculum that is available for infecting chile plants later in the season.