Glyphosate Injury to Sweetpotatoes Adjacent to Field Roads
Maintaining clean and weed-free field roads around sweetpotatoes is thought to help minimize rodent injury and make access for crop scouting and monitoring more efficient. Roads are most often maintained weed-free with glyphosate applications. However, off-target movement of glyphosate onto adjacent sweetpotato plants can be problematic.
Sweetpotato vines exposed to glyphosate often exhibit chlorotic/yellow leaves and stems near the youngest portion of the developing vine (Figure 1). Sweetpotato response to off-target glyphosate exposure is dependent upon exposure rate and the stage of the crop. Glyphosate applied to four-week-old sweetpotato vines is often lethal. However, crop tolerance increases at six weeks after transplanting and increases again at eight weeks. Sweetpotato vines exposed to off-target glyphosate often have reduced yields and increased incidence of storage root cracking (Figure 2).
The vining nature of sweetpotato shoots makes it difficult to avoid contact with the crop completely, but exposure can be reduced by increasing droplet size (using a higher volume nozzle at a lower pressure) and avoiding excessive boom height.
At harvest, instruct laborers to be mindful of cracked roots along field edges and avoid including them in bins with otherwise healthy storage roots.