Eight hard red spring wheat cultivars were tested for tolerance to five postemergence grass herbicides at two locations in Minnesota in 1999 and 2000 at the labeled, one and one-half, or twice the labeled rate. Fenoxaprop plus safener and ICIA 0604 caused the least injury and did not reduce grain yield for most cultivars. Flucarbazone caused intermediate injury and a slight decrease in grain yield for half the cultivars tested. Difenzoquat caused the most injury, regardless of whether the cultivar was genetically sensitive to difenzoquat. Tank-mixing difenzoquat with imazamethabenz reduced injury, even for cultivars that were not genetically sensitive to difenzoquat. Drought stress before application of the postemergence grass herbicides that contain difenzoquat resulted in more potential for crop injury. Excess precipitation combined with high temperatures after application resulted in more potential for crop injury for the other postemergence grass herbicides included in this experiment.

Nomenclature: Difenzoquat; fenoxaprop; flucarbazone; ICIA 0604 (proposed common name, tralkoxydim; 2-cyclohexen-[1-one,2-]1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)-(9CI)); imazamethabenz; wheat, Triticum aestivum L. emend. Thell.

Additional index words: Crop injury, herbicide tolerance.

Abbreviations: HRSW, hard red spring wheat.