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

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Abstract
In a field trial at Pukekohe the effect of sprinkler irrigation and wide ridging (91 cm) on potato infestation by the potato tuber moth Phthorimaea operculella Zell., Lepidoptera, Gelechiidae was assessed in a season of unusually low rainfall. Infestation of table grade tubers was 10% under sprinkler irrigation compared with 86% under no irrigation. Irrigation increased tuber yield four-fold. The combined effects of irrigation on tuber infestation plus yield produced a 27.9-fold increase in marketable potatoes, from 1513 kg/ha to 41 297 kg/ha. Wide ridging was associated with reduced infestation of table grade tubers. Closer spacing of seed to maintain correct plant density per hectare did not affect tuber yield. No interaction between irrigation and row width was detected. Irrigation reduced foliage-mining intensity (number of miners per unit available leaf). As the crop matured, foliage was denser under irrigation, and the actual population level (number of miners per unit land area) was higher than under no irrigation.