Sensitivity of winter wheat to preplant and preemergence glyphosate tankmixes

Field experiments were established at the Huron Research Station and at the University of Guelph Ridgetown Campus in the autumn of 2004 and 2005 to evaluate the tolerance of winter wheat to tankmixes of glyphosate plus either amitrole, dicamba, dicamba/diflufenzopyr, 2,4-D amine, 2,4-D ester, chlorimuron-ethyl or thifensulfuron-methyl/tribenuron-methyl applied either preplant (PP) or preemergence (PRE). Contrasts comparing PP vs PRE treatments showed no difference in visible injury, plant height and yield between application timings. The tankmixes of glyphosate (1800 g ha−1) plus either amitrole (1155 g ha−1), dicamba (300 g ha−1), 2,4-D amine (700 g ha−1), 2,4-D ester (700 g ha−1) or thifensulfuron-methyl/tribenuron-methyl (15 g ha−1) caused minimal (less than 6%) and transient visible injury in winter wheat. In addition, these tankmixes had no effect on plant height and yield. The tankmix of glyphosate (1800 g ha−1) with dicamba/diflufenzopyr (200 g ha−1) or chlorimuron-ethyl (9 g ha−1) caused as much as 8 and 18% visible injury in winter wheat, respectively. Glyphosate (1800 g ha−1) plus dicamba/diflufenzopyr (200 g ha−1) did not affect plant height but glyphosate plus chlorimuron-ethyl reduced plant height 11%. Yield was reduced 15% when glyphosate was tankmixed with dicamba/diflufenzopyr and 26% when glyphosate was tankmixed with chlorimuron-ethyl.