Cultural practices in relation to infestation of potato crops by the potato tuber moth

Abstract

In field trials at Pukekohe the effects were assessed of increased seed depth, re‐moulding, pre‐harvest defoliation, and delayed harvest on infestation of potato tubers by Phthorimaea operculella (Zeller). Tuber damage was halved by planting seed 25 cm below the ridge apex rather than the standard 18 cm. Re‐moulding at flowering reduced tuber damage in one trial, but was ineffective in another. Mechanical defoliation of infested foliage before harvest was associated with increased tuber infestation, which was evident only at second grading 12 days after harvest. Chemical defoliation showed a direct correlation between foliar and re‐graded tuber infestation levels, but the tuber infestation level was not significantly greater than control. A 2–4 weeks' delay in harvest resulted in increased levels of tuber infestation, indicating that adults are attracted to, and will oviposit in, potato crops in the absence of foliage.