Mutation of a cytochrome P450 (CYP) allele on the short armof chromosome 5 affects sensitivity in sweet corn to mesotrione and totembotrione plus isoxadifen applied POST. Hybrids that are homozygous forthe functional allele (i.e., CYPCYP) are rarely injured atregistered use rates, hybrids that are homozygous for mutant alleles (i.e., cypcyp) are frequently injured, and hybrids that areheterozygous for a functional and mutant allele (i.e., CYPcyp) have more variable responses over trials. Theobjectives of this work were (1) to conduct side-by-side comparisons ofsweet corn hybrid responses to mesotrione, tembotrione plus isoxadifen, andtopramezone under field conditions; and (2) to compare dose–responserelationships among CYPCYP, CYPcyp, and cypcyp hybrids. Among 4-hydroxyphenylpyruvatedioxygenase (HPPD) inhibitors used POST in sweet corn, topramezone was safeon the 746 hybrids tested. When environmental conditions favored cropgrowth, mesotrione injured the largest number of hybrids, and these hybridswere almost exclusively cypcyp or CYPcyp.The safener isoxadifen added to the tembotrione product greatly reducedoccurrence of injury to the CYPcyp genotypic class but notto the cypcyp hybrids. Despite a common genetic basis forherbicide metabolism, genotypic classes of sweet corn hybrids did not haveidentical field responses to mesotrione, tembotrione plus isoxadifen, andtopramezone.