Both genetically-modified (GM) and non-modified baculoviruses were tested alone and with an ovicide for control of cotton bollworm, Helicoverpa zea (Boddie), in Bt and conventional cotton. GM viruses, engineered for faster kill (Dupont), were compared to a conventional virus (Dupont) and to Asana™ in Bt and conventional cotton in 1998. In 1999, bollworm populations were very low and did not reach treatment thresholds in Bt cotton. Therefore, the viruses were compared with a Karate™ standard only in conventional cotton. In 1998 in conventional cotton, bollworm populations were significantly lower in all treatments compared to untreated checks, however only the Asana™ standard gave adequate control. In 1998 in Bt cotton the GM virus IC917-11 with IC848-14 (Dupont) and the pyrethroid Asana™ both provided significantly better control than the untreated checks. In 1999, on conventional cotton, all virus treatments were significantly better than check plots and combinations with an ovicide substantially improved the efficacy of the viruses.