Field assessment of several insecticides against the potato tuber moth ( <i>Phthorimaea operculella</i> Zell. Lepidoptera, Gelechiidae) at Pukekohe

Abstract

Abstract Field trials at Pukekohe of insecticides against potato tuber moth ( Phthorimaea operculella Zell.) showed that little direct control of tuber infestation was achieved. Foliage infestation, however, was effectively controlled; and this indirectly effected a reduction in tuber infestation, as long as nearby areas were also clean. Although both recommended insecticides, azinphos ethyl and endosulfan, were effective against foliage mining under low to moderate population pressure, only azinphos ethyl was consistently effective under high to extreme pressure. Four additional candidate insecticides (ENT 27041, acephate. methamidophos, and chlorpyrifos) were compared with azinphos ethyl, but none proved as good, although acephate showed some promise. The standard aphicide oxydemeton methyl was found to have a small but significant effect on the foliage‐mining population. It was found that 4.8% of infested tubers escaped detection at harvest grading because young mines and eggs are not easily seen. As a result, it is recommended that table grade tubers be re‐sorted 7–14 days after the first sorting.