The 2009 ASHS Annual Conference

Field research was conducted to evaluate Russet Burbank growth the same year simulated glyphosate drift occurred to irrigated potatoes.  Glyphosate was applied at rates one-third, one-sixth, and-twelfth, and one-twenty-forth the standard use rate (0.25, 0.125, 0.0625, and 0.0313 lb ae/A) at the tuber hooking (TH) 0.25 lb ae/A only, tuber initiation (TI), early tuber bulking (EB), and late tuber bulking stage (LB).

In 2007, total yield from potatoes treated with glyphosate at the TH stage was significantly lower than any other treatment (88 cwt/A).  This was followed by potatoes treated with 0.25 lb/A glyphosate at the TI stage (187 cwt/A).  Only plants treated with 0.25 lb/A glyphosate at the TH, TI, and LB stages or with 0.125 lb/A glyphosate at the TI stage yielded less marketable tubers than the untreated due to an increase in cull tubers. Fewer 4 to 6 oz tubers were produced when potatoes were treated with 0.25 lb/A glyphosate at the TH stage.  Likewise, fewer 6 to 10 oz tubers were produced when potatoes were treated with 0.25 lb/A glyphosate at the TH and TI stages.  Fewer >10 oz tubers were produced when plants were treated with 0.25 lb/A glyphosate at the TH, TI, or LB stages, or when treated with 0.125 lb/A glyphosate at the TI stage. 

In 2008, total yield from plants treated with 0.25 lb/A glyphosate at the TH, TI, and EB stages or with 0.125 lb/A glyphosate at the TI and EB stages were significantly lower than any other treatment, except 0.063 lb/A glyphosate at the TI stage.  Results were similar for marketable tubers except that plants treated with 0.063 lb/A glyphosate at the TI stage also had significantly less marketable tubers due to an increase in cull tubers.   Fewer 4 to 6 oz tubers were produced when potatoes were treated with 0.25 lb/A glyphosate at the TH, TI, and EB stages.  Likewise, fewer 6 to 10 oz tubers were produced when potatoes were treated with 0.25 lb/A glyphosate at the TH, TI, and EB stages, or with 0.125 lb/A glyphosate at the TI and EB stages, or with 0.063 lb/A glyphosate at the TI stage.  Fewer >10 oz tubers were prduced when plants were treated with 0.25 lb/A glyphosate at the TH, TI, or LB stages, or when treated with 0.125 lb/A glyphosate at the TI and EB stages, or when treated with 0.063 lb/A glyphosate at the TI stage.