Effect of Planting Depth and Irrigation Regimes on Potato Tuberworm (Lepidoptera: Gelechiidae) Damage Under Central Pivot Irrigation in the Lower Columbia Basin.

Phthorimaea operculella Zeller has proven to be a limitation to potato production. Although pesticides can effectively reduce P. operculella populations, information regarding effective cultural controls is lacking. The following study was designed to evaluate the effect of different irrigation regimes and planting depths to reduce P. operculella damage under central pivot irrigation. Field trials were conducted in 2007 and 2008 and experimental plots followed standard growers' agronomic practices. Three levels of irrigation were used: optimal, 10% less than optimal, and 10% above optimal; potato planting depth was arranged as shallow, normal, and deep; normal planting was considered tubers planted at 0.15 m depth. Mines and number of larvae per plant were counted weekly until harvest and tuber damage, above and below ground, was estimated. Overall, irrigation had a stronger effect than planting depth but there were not a clear planting depth:irrigation interaction. Both years, sampling dates had a strong effect on the number of mines per plant where the number of mines per plant increased as season progressed. There were not clear trends related to mines per plant, mines per tuber or yield related to planting depth, but there were strong tendencies related to irrigation. The data presented herein provide valuable information regarding the potential to adjust irrigation to warrant better P. operculella control.