When glyphosate treatments occur next to a potato field or the same sprayer is used to treat potatoes with pesticides that has been used for glyphosate, there is the risk that glyphosate may contact potato plants. Glyphosate enters the potato plant through the leaves or shoots and then translocates to the growing points above and below ground. During daughter tuber development, tubers act as a “sink,” or a place to accumulate assimilates produced by the leaves and other exogenous compounds (such as glyphosate) translocated by the plant. Glyphosate injury can appear as a yellowing or necrosis in young leaves, plants can be stunted in growth, and this can affect the yield potential and tuber quality.
Various research reports that potato response varies by potato cultivar, glyphosate rate, and timing. Russet Ranger potatoes had an estimated 10% reduction in yield when 1.1 to 2.2 oz/acre (5-10% of 22 oz/acre) of glyphosate was applied to 4 inch tall potatoes in a study in Oregon. In the same study, potatoes were most sensitive to glyphosate when in the hooking stage, which only took an estimated 0.6 to 0.8 oz/acre (3-4% of 22 oz/acre) of glyphosate to cause a 10% yield reduction. Studies have shown that up to 16% of a spray solution can drift when ground applied with a 19 mph wind. Drift can be reduced by nozzle selection, pressure, boom height, travel speed, and not spraying when wind speeds are high.
Sprayer contamination is also a concern for all herbicide applications. This is especially true when spraying a potato crop following the use of a non-friendly potato herbicide in the sprayer. Rinsing with just water may not remove the residue and the herbicide may remain tightly adsorbed in the sprayer through several loads. Further loads that contain other herbicides, oils, fertilizers, or basic pH blend may cause the herbicide to desorb, disperse into the spray solution, and damage susceptible crops.
I have observed a potato field with dicamba injury that was determined to come from dicamba residues left in the sprayer from a dicamba application to a corn field three tanks earlier. More information on sprayer cleanout can be found in the NDSU Weed Guide on page 79.
Seed potatoes generally are most affected when glyphosate contacts potatoes during the bulking stage. However, in a year like we are in with late planting dates, any inhibition in growth and development will have a greater effect on the plant’s yield potential. Be vigilant in your spraying, communicate with your neighbors and let them know the locations of your potato fields, and if that does not work consider planting a border around the potatoes.