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An integrated approach to controlling white grubs in forestry

Benice Sivparsad: Institute for Commercial Forestry Research

<div>In South Africa (SA), white grubs are the dominant and most economically important soil invertebrate pest during forest establishment. An effective control measure for soil-borne pests is deltamethrin, a chemical banned by the Forest Stewardship Council (FSC) but used by the SA forestry industry under temporary derogation. Therefore, there is an urgent need to find alternative chemical and biological control measures that will comply with FSC regulations in the management of soil pests. This study was initiated to (1) evaluate alternative ecologically sound insecticides and biologicals to reduce the impact of white grub feeding on post-plant performance and (2) monitor the incidence of white grub in selected sites to provide spatial and temporal trends of pest activity. Results of pot trial evaluations indicated that biological products containing azadirachtin, potassium silicate and <em>Beauveria brongniartii</em>, and chemical products containing imidacloprid and clothianidin, protected wattle and eucalypt seedlings from white grub damage. In addition, treatment with imidacloprid and <em>B. brongniartii</em> significantly reduced final mortality of wattle seedlings to 33% and 50% respectively. Temporal sampling of selected wattle, pine, and eucalypt sites have indicated that a greater white grub population and diversity is found in wattle sites that are in close proximity to sugarcane fields. Five morphospecies have been tentatively identified based on differential rasta patterns. These include: <em>Maladera</em> spp., <em>Pegylis sommeri</em>, <em>Adoretus ictercus</em>, <em>Schizonycha affinis</em> <em>and Schizonycha fimbriate. </em>Results of this study will form a basis for the formulation of an integrated approach for the control of soil-borne pests in forest regeneration.</div>