Biological control of two spotted spider mite Tetranychus urticae on ornamental nursery plants using the predatory mite Phytoseiulus persimilis
1987
Hart, R.N.S. (Hawkesbury Agricultural Coll., Richmond, New South Wales (Australia). Faculty of Horticulture)
The effectiveness of the predatory mite Phytoseiulus persimilis Athias-Henriot in controlling Tetranychus urticae in outdoor ornamental plants was investigated in a commercial trial at a plant nursery near Sydney. The trial, which was not able to be fully replicated, consisted of four thousand and potted Gardenia jasminoides which were evenly divided into two "release" treatment blocks and two "non-release" control blocks. Approximately 10,000 P. persimilis were uniformly distributed in each of the release blocks into existing T. urticae infestations. One hundred leaves were sampled from each block nine times during the trial period at approximately weekly intervals to determine levels of both mite species. For T. urticae, leaves were individually scored on a 0-6 rating where active stages of mites/leaf of 0,1-3,4-10, 11-20, 21-60, 61-100 and 100 were represented by ratings 0, 1, 2, 3, 4, 5 and 6 respectively. Predator numbers were scored as absence/presence expressed as percentage. Blocks were treated with miticides cyhexatin and chlofentezine only when mite damage was so severe as to render plants unsaleable. In release blocks, T. urticae levels decreased from an initial mean score of 1.95 to 0.09 in eight weeks. Only one reading (one week after release) exceeded the initial level. Predator numbers remained low (10 %) for the majority of the trial period, but reached a maximum (50 %) seven weeks after release. In non-release blocks T. urticae levels increased from an initial mean scope of 1.90, reaching a maximum of 2.64. This level of mite activity severely blemished the plants and necessitated one application each of cyhexatin and chlofentezine. The trial indicates that there is a potential for the use of P. persimilis to suppress T. urticae in ornamental plants produced outdoors under Australian conditions.
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