Cultural practices and insecticide treatments and combinations were evaluated for effect on tuber damage by potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) in the Columbia basin of eastern Oregon and Washington. A range of intervals between initial application of several insecticides and vine-kill were tested to determine how early to implement a program to control potato tuberworm tuber damage. Esfenvalerate, methamidophos, and methomyl were applied at recommended intervals, with programs beginning from 28 to 5 d before vine-kill, All insecticide treatments significantly reduced tuber damage compared with the untreated control, but there was no apparent advantage to beginning control efforts earlier than later in the season. Esfenvalerate and indoxacarb at two rates and a combination of the two insecticides were applied weekly beginning 4 wk before and at vine-kill, and indoxacarb was applied at and 1 wk postvine-kill as chemigation treatments. Application of insecticides at and after vine-kill also reduced tuberworm infestation. ‘Russet Norkotah’ and ‘Russet Burbank’ plants were allowed to naturally senesce or were chemically defoliated. They received either no irrigation or were irrigated by center-pivot with 0.25 cm water daily from vine-kill until harvest 2 wk later. Daily irrigation after vine-kill reduced tuber damage, and chemical vine-kill tended to reduce tuber damage compared with natural senescence. Covering hills with soil provides good protection but must be done by vine-kill. Data from these trials indicate that the most critical time for initiation of control methods is immediately before and at vine-kill.
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Vol. 103 • No. 4