Two corn hybrids were evaluated to determine tolerance to foramsulfuron applications with and without the safener, isoxadifen-ethyl at five application timings. The corn hybrid N58D1 was more sensitive to foramsulfuron applications than N59Q9. Averaged across all application timings, the addition of isoxadifen-ethyl decreased corn injury of the more sensitive corn hybrid, N58D1. Foramsulfuron application timing had a significant effect on corn tolerance. The greatest corn injury generally occurred from foramsulfuron applications to V6 and V8 corn (visible collars). Foramsulfuron injury ranged between 9 and 37% from these two application timings, 7 d after treatment (DAT). By 21 DAT, corn generally recovered from foramsulfuron injury, and there were a few cases of reduced corn yield at the end of the season. Yield reductions and ear malformations were greatest at the Urbana location with both hybrids when foramsulfuron was applied to V12 corn. The addition of isoxadifen-ethyl alleviated ear malformations and increased corn yield from this application timing. Applications of foramsulfuron before V6 corn also were important in reducing corn injury and protecting yield. Therefore, when growers are using foramsulfuron for weed control, it will be important to select proper hybrids that are more tolerant as well as making applications before V6 corn.

Nomenclature: Foramsulfuron; corn, Zea mays L.

Additional index words: Application timing, crop tolerance, hybrid sensitivity.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAT, days after treatment; POST, postemergence; WAP, weeks after planting.