Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/21/2010
Publication Date: 7/1/2010
Citation: Williams, M., Pataky, J.K. 2010. Factors Affecting Differential Sweet Corn Sensitivity to HPPD-inhibiting Herbicides. Weed Science. 58:289-294. Interpretive Summary: We compared sweet corn hybrid sensitivity to three of the newest herbicides used in corn - mesotrione, tembotrione, and topramezone. Examining 746 sweet corn hybrids under field conditions, we found the hybrids do not have a similar response to the herbicides at a two-fold use rate. Mesotrione injured the largest number of hybrids, whereas topramezone injured none. When plants were exposed to a range of herbicide doses in the greenhouse, a clear pattern emerged. As the number of functional alleles involved in herbicide metabolism increased from zero to two in the hybrids, a higher dose of herbicide was required to cause crop injury. The fact that hybrids had different responses to the three herbicides under field conditions is explained by 1) differences among the herbicides in their registered use rates, and 2) only one herbicide (tembotrione) is formulated with a safener that enhances herbicide metabolism. The impact of this work is being the most extensive report of a side-by-side comparison of corn hybrid response mesotrione, tembotrione, and topramezone. It gives those who provide weed management recommendations (i.e. extension personnel, industry representatives, consultants, and growers) knowledge of the crop injury risks associated with use of the herbicides. It also provides justification for genetic improvements of herbicide tolerance in sweet corn.
Technical Abstract: Mutation of a cytochrome P450 (CYP) allele on the short arm of chromosome five affects sensitivity in sweet corn to mesotrione and tembotrione+isoxadifen applied POST. Hybrids that are homozygous for the functional allele (i.e. CYPCYP) are tolerant of both herbicides and rarely injured at registered use rates, while hybrids that are homozygous for mutant alleles (i.e. cypcyp) are frequently injured. Responses to mesotrione and tembotrione+isoxadifen differ between hybrids that are heterozygous for a functional and mutant allele (i.e. CYPcyp). Reports of injury to sweet corn from topramezone are scarce. Examination of responses of CYPCYP, CYPcyp and cypcyp hybrids to these herbicides under common conditions is nonexistent. The objectives of this work were 1) to conduct side-by-side comparisons of sweet corn hybrid responses to mesotrione, tembotrione+isoxadifen, and topramezone under field conditions, and 2) to compare dose-response relationships among CYPCYP, CYPcyp, and cypcyp hybrids. Among HPPD-inhibitors used POST in sweet corn, topramezone was safe on the 746 hybrids tested. When environmental conditions favored crop growth and subsequent injury (e.g. typical moisture conditions preceding application), mesotrione injured the largest number of hybrids and these hybrids were almost exclusively cypcyp or CYPcyp. The safener isoxadifen added to the tembotrione product appeared to greatly reduce occurrence of injury of CYPcyp hybrids, but not of cypcyp hybrids. Despite a common genetic basis for cytochrome P450 metabolism of these herbicides, sweet corn hybrids did not have identical field responses to mesotrione, tembotrione+isoxadifen, and topramezone, in part because inherent differences in product formulations resulted in differential responses of hybrids in the three genotypic classes.