Sensitivity of Three Red Potato Cultivars to Glyphosate Drift

Field research was conducted at the Northern Plains Potato Grower’s Association Research site near Grand Forks, ND to evaluate Red Lasoda, Red Norland, and Sangre response to glyphosate simulated drift that may have occurred to plants at one of three growth stages.  Glyphosate was applied at rates one-third, one-sixth, and one-twelfth the standard use rate (0.25, 0.125, and 0.0625 lb ai/A) at the tuber initiation (TI), early tuber bulking (EB), and late tuber bulking stages (LB). 

Seed pieces (2 oz) were planted on 36-inch rows and 12-inch spacing on June 10, 2009.  Plots were 4 rows by 25 ft arranged in a split-block design with cultivar as the main factor and the combination of application timing and herbicide rate as sub-plots with 3 replicates.  Glyphosate was applied with a CO₂ pressurized sprayer equipped with 8001XR flat fan nozzles with a spray volume of 5 GPA and a pressure of 35 psi.  The first application timing (TI) occurred on July 23, 2009.  Extension recommendations were used for cultural practices throughout the year.

Red Norland was the most sensitive cultivar to glyphosate.  Plants treated with glyphosate at the TI stage or with at least 0.125 lb ai/A glyphosate at the EB stage produced significantly more cull tubers (< 4 oz) compared to the untreated control and reduced marketable yields 37 to 50%.  Unfortunately, excessive tuber cracking and russet skinning occurred with most of the tubers in these application timings, further reducing marketable yields. 

Red LaSoda was the next most sensitive cultivar to glyphosate.  Plants treated with 0.25 lb ai/A glyphosate at the TI stage or with at least 0.125 lb ai/A glyphosate at the EB stage produced significantly more cull tubers (< 4 oz) compared to the untreated control and reduced marketable yields 34 to 57%.  Excessive tuber cracking and russet skinning was most severe in the EB stage with 70 to 100% rejection of marketable tubers due to visible tuber defects.

Sangre was the least sensitive tested cultivar to glyphosate.  Plants treated with 0.25 lb ai/A glyphosate at the TI or EB stage produced significantly more cull tubers (< 4 oz) compared to the untreated control and reduced marketable yields 31 to 58%.  Excessive tuber cracking and russet skinning was most severe in the EB stage with 30 to 100% rejection of marketable tubers due to visible tuber defects.