Abstract: Field studies were conducted in 1998 and 1999 at Simcoe and Exeter, ON, to evaluate the tolerance of nine sweet corn cultivars, representing a range of genotypes, to RPA 201772 applied preemergence at 105 and 210 g ai/ha. The location × year interaction was significant for visible plant injury, plant height, and yield. All cultivars showed significant injury at Simcoe in 1999, especially at 210 g/ha. Calico Belle was the most sensitive cultivar, with RPA 201772 resulting in severe injury at Simcoe in 1999. Increased injury in 1999 was due to significant rainfall (48.5 mm) within 10 d of RPA 201772 application at Simcoe. Calico Belle also showed injury at Exeter in 1999 and at Simcoe in 1998. Plant height of all cultivars was reduced at the Simcoe location in 1999. Yield of five cultivars was also reduced at Simcoe in 1999. Sensitivity to RPA 201772 increased as application rate increased. Plant height and yield was not reduced at Exeter.

Nomenclature: RPA 201772 (proposed common name, isoxaflutole), 5-cyclopropyl-isoxazol-4-yl 2-mesyl-4-trifluoromethyl phenyl ketone; sweet corn, Zea mays L.

Additional index words: Plant height, crop injury, preemergence, benzoly isoxazole.

Abbreviations: DAT, days after treatment; OM, organic matter; PRE, preemergence.