Late-Season Irrigation Influences French Fry Color

Given the increasing challenges of water scarcity and the stringent quality requirements of the frozen potato-processing industry, this multi-year research trial aimed to determine whether reduced late-season irrigation on potatoes could improve French fry color. The study was conducted near Othello, WA, and was comprised of five irrigation levels: 40%, 60%, 80%, 100%, and 120% of modeled evapotranspiration (ET), and five potato cultivars: Alturas, Clearwater Russet, Ranger Russet, Russet Burbank, and Umatilla Russet. Irrigation treatments started 100 to 105 days after planting (DAP), approximately 1500 day degrees (at or near peak canopy growth), and ended at vine kill, 150 to 155 DAP. Fry color was assessed following storage durations of 45 and 90 days after harvest from three storage temperatures of 4.4 °C, 6.7 °C, and 8.9 °C, using a photovolt reflectometer, measuring percent light reflectance, in which higher values represented lighter fries. The study found that reducing late-season irrigation generally improved overall fry color. Fry color improvements were observed in four potato cultivars grown with 20% to 40% less irrigation than the control (100% ET); Ranger Russet exhibited no improvement. Reducing late-season irrigation by more than 40% resulted in darker fries for Clearwater Russet, Russet Burbank, and Umatilla Russet when tubers were stored at 4.4 °C and 6.7 °C. Excess irrigation, greater than 100% ET, generally darkened fries in Alturas, Clearwater Russet, Russet Burbank, and Umatilla Russet. These findings provide valuable guidelines for potato growers, indicating that while reducing late-season irrigation can enhance fry color, the effects may depend on a combination of cultivar, irrigation level, and storage temperature.