Control of beet armyworm larvae was tested in Northern Mexico in Chihuahua and Tamaulipas under commercial cotton and lab conditions from July to September 1996 with a growth regulator insecticide, Confirm 2F. This insecticide showed rapid, satisfactory control of beet armyworm larvae. From Ll to L2 were killed in 2-3 days. Under lab conditions, L4 larvae were killed in 2-4 days, but in commercial cotton beet armyworm larvae needed 6-8 days to die, due mainly to higher temperatures in the lab than in the field. Literature reports Confirm action is affected by low temperature. Confirm 2F was applied at 330 cc/ha in commercial cotton (4 Has.) that had 3-5 larvae/lineal meter. The main species of beneficial insects present, Chrysopa and Cotesia marginiventris, were not affected by this insecticide. The product appears useful for IPM programs for cotton growers.