TIMING OF INSECTICIDE APPLICATIONS FOR CONTROL OF SOFT WAX SCALE (HOMOPTERA, COCCIDAE) ON CITRUS

The efficacy of four insecticide treatments-buprofezin, chlorpyrifos, 1 and 2% mineral oil, applied at four single, and a double application time, was evaluated against soft wax scale, Ceroplastes destructor Ne wstead, on 'Seminole' tangelo (Citrus paradisi (Macfadyen) x C. reticu lata (Blanco)) in Kerikeri, New Zealand. Settlement of the insecticide -sensitive ray stage(1st instar and 2nd instar) onto leaves, and the l ater dispersal of rays onto the wood to form the wax-protected peak st age (3rd instar), was monitored. Spray application times on 15 and 25 January, 12 February, and 2 March 1993 corresponded to 64, 96, 100, an d 50% of total ray abundance on leaves in untreated trees. Maximum ray abundance, after correcting for natural mortality, was estimated to o ccur on 4 February. There was no significant difference between chlorp yrifos and both mineral oil treatments which resulted in 71 and 90% co ntrol of rays, when averaged over all single and double applications, respectively. The highest level of control was achieved about the time of maximum ray settlement and insecticides should be applied during t he period, 18 days before and 28 days after maximum settlement. A long er-term evaluation of the success of treatments showed that all treatm ents significantly reduced peak stages in April by 71%, averaged over all times of application. The 1% mineral oil treatment was the preferr ed choice in an integrated pest management programme.