Chemigation of various rates of cypermethrin emulsifiable concentrate (EC) and technical grade formulations, and a single formulation of esfenvalerate, resulted in varying mortality of Helicoverpa zea (Boddie) neonate larvae. Mortality rates decreased throughout the 120-h posttreatment exposure period. Cypermethrin active ingredient rate was not as important a factor in bollworm mortality as was the time of sampling after the treatment. Application of cypermethrin EC mixed with Orchex^® 796 non-EC petroleum oil resulted in greater mortality of bollworm larvae than did cypermethrin EC mixed with water. Neither the duration of residual activity nor the percentage bollworm mortality was influenced by the formulation of cypermethrin.