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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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Cao, Yong 1989 , 'Biological and ecological studies of two spotted spider mite (Tetranychus urticae Koch) and its control on hops in Tasmania', Research Master thesis, University of Tasmania.

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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.

Item Type: Thesis - Research Master
Authors/Creators:Cao, Yong
Keywords: Tetranychidae, Mites
Copyright Holders: The Author
Copyright Information:

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).

Additional Information:

Includes bibliographical references (p. 257-278). Thesis (M.Agr.Sc.)--University of Tasmania, 1991

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