Sweet potato weevil (Cylas formicarius) incidence in the humid lowlands of Papua New Guinea

K.S. Powell, A.E. Hartemink, J.F. Eganae, C. Walo, S. Poloma

Research output: Chapter in Book/Report/Conference proceedingChapterAcademicpeer-review


Sweet potato is the main staple crop in PNG and this paper presents a study from the humid lowlands of the Morobe Province. Three experiments were carried out at two locations (Hobu and Unitech) to evaluate the effect of inorganic fertiliser inputs and fallow vegetation on the incidence of sweet potato weevil, Cylas formicarius (Coleoptera: Brentidae), and damage to sweet potato (Ipomoea batatas) under natural levels of infestation. Nitrogen and potassium application at rates from 0 to 150 kilograms per hectare and 0 to 50 kilograms per hectare, respectively, and fallow vegetation treatments of Imperata cylindrica, Piper aduncum or Gliricidia sepium, had no significant effect on sweet potato weevil incidence and tuber damage over two consecutive seasons. At Hobu, the mean tuber damage category in the continuous sweet potato treatment was slightly higher than fallow treatments in two consecutive seasons, though not significantly so. In the second season, there was a 20-fold increase in the numbers of weevil stages found in damaged tubers of the continuous sweet potato treatment. Differences in above-ground weevil incidence were recorded between sites with up to 28.5 weevils per square metre at Unitech and a maximum of 0.5 weevils per square metre at Hobu. Levels of tuber and vine damage also differed between sites. At the Hobu site, despite low above-ground weevil incidence, vine and tuber damage was high over consecutive seasons with more than 51% of vines and 34% of tubers damaged. At Unitech, vine damage was consistently above 83%, yet tuber damage did not exceed 16%. Tuber damage, although sometimes high in terms of the percentage of tubers damaged, was superficial at both sites. This had little effect on marketability or yield as low levels of weevil life stages were recorded in the tubers. Site-related differences, in particular rainfall, soil properties and cultivar characteristics may have contributed to the relatively low levels of tuber damage compared with the high levels of weevil incidence on the vines and foliage
Original languageEnglish
Title of host publicationFood Security for Papua New Guinea
Place of PublicationCanberra
Publication statusPublished - 2001

Publication series

NameACIAR Proceedings
PublisherAustralian Centre for International Agricultural Research


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