Atrazine Accentuates Carryover Injury from Mesotrione in Vegetable Crops

Trials were established in 2003, 2004, and 2005 in Ontario to determine the effects of residues of mesotrione, atrazine, and mesotrione plus atrazine 1 and 2 yr after application on broccoli, carrot, cucumber, onion, and potato. One yr after mesotrione application, injury was 43, 37, 18, 24, and 0% in broccoli, carrot, cucumber, onion, and potato, respectively. The addition of atrazine to mesotrione in the year before planting increased injury to 55, 53, 30, 42, and 3% in broccoli, carrot, cucumber, onion, and potato, respectively. Plant dry weight and yield were also decreased by mesotrione residues the year after application in all crops except potato. The addition of atrazine to mesotrione accentuated the reduction in dry weight and yield in broccoli, carrot, cucumber, and onion. There was no injury, or reductions in dry weight or yield in any crop planted 2 yr after application of mesotrione alone or in tank mix with atrazine. A recropping interval of 2 yr is recommended following applications of mesotrione or mesotrione plus atrazine for broccoli, carrot, cucumber, and onion. Potato can be safely planted the year following application of mesotrione plus atrazine.