Field experiments were conducted to determine establishment of fall armyworm, Spodoptera frugiperda (J.E. Smith), infestations on whorl stage sorghum when larvae in different stages were reared on either sorghum foliage or wheat germ based diet and artificially inoculated onto the plants. No differences were observed in numbers of larvae per plant on days 1, 2, 6 or 12 after infestation when plants were inoculated with third instar larvae reared on sorghum foliage or wheat germ diet. Inoculations using first or third instars at day 1, 6 or 12 after infestation were not compared because of non-significant interactions. However, at day 2 after infestation and when first instar larvae were used, the mean numbers of larvae per plant were greater when inoculations were made at 7:00 am and 1:00 pm than at 6:00 pm, whereas when third instar larvae were used a greater number of larvae was on the infested plants when inoculated at 7:00 am than at 1:00 pm or 6:00 pm. For experimentation, it is better to inoculate whorl stage sorghum with first or third instar fall armyworm larvae reared on either sorghum foliage or wheat germ diet during early morning than later during the day to obtain suitable survival of larvae to successfully establish infestations of this pest.