University of Tasmania
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Biological and ecological studies of two spotted spider mite (Tetranychus urticae Koch) and its control on hops in Tasmania

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posted on 2023-05-27, 08:37 authored by Cao, Yong
This study was initiated in March 1987 and completed in March 1989. Aspects of the general biology and ecology of Two Spotted Spider Mite (TSSM), Tetranychus urticae Koch, and its natural enemies in hop fields were investigated in the years 1987-88 and 1988-89. The investigation found that TSSM overwinters in hollow cavities of hop twigs in the litter around hop rootstocks. In late August to early September TSSM becomes active to lay eggs and progressively colonizes hop on the lower surface of hop leaves. The teneral female mites of new generations were found to move upward with elongation of hop vines.The distribution patterns of the mites on hops vary with time and mite stage. In early or mid-March, mites move downward along hop vines to seek overwintering refuges. The native predatory mite, Amblyseius longispinosus (Evans), was found to overwinter in the litter around the hop base. While the imported predatory mite, Phytoseiulus persimilis Athias-Henriot, cannot survive the Tasmanian winter. The effects of TSSM feeding on hop production and the control of TSSM on hops by various means were studied in the two consecutive seasons. If unchecked, the mite can cause as much as 30% loss in cone production. The loss is mainly due to the reduction in numbers of cones hop plants produce under high mite feeding pressure. Damage was most often associated with large numbers of immature TSSM. However, mite populations can be effectively suppressed by either multiple application of Summer-oil/ Limesulphur, or the release of predacious mite P. persimilis at appropriate time. A tolerance to mite feeding by hop plants was demonstrated. If insufficient numbers of cones are formed due to mite infestation, hop plants will produce larger cones to achieve maximum production. Two cultural activities can be effectively included into a TSSM control programme. Ploughing hop fields in late August - early September, after overwintering adults have moved onto notably thistles, can retard the build up of TSSM populations. Furthermore frequent use of overhead sprinkler irrigation of hop fields can result in suppression of TSSM populations. Several simple ways of assessing TSSM densities on hops were assessed in 1987-88 and were employed throughout this study. A 'modified counting method' was developed for estimating mite densities using a mite-brushing machine. Adult female mite densities were estimated in hop fields by the naked eye and these counts related to total numbers of all mite stages. In the phenology of the hop plant economic damage by mites was caused through infestation during the flowering phase and not by infestation of the earlier vegetation growth phase. Trial results indicated that application of Summer-oil during the post-vegetation phase could provide a potential alternative to conventional miticides.


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The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Includes bibliographical references (p. 257-278). Thesis (M.Agr.Sc.)--University of Tasmania, 1991

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