Pot trial assessment of alternative chemical and biological products for the control of white grub on wattle and eucalypt seedlings

Sivparsad BJ, Nadel R, Morris A
Publication Type
Technical Note
Publication Year

In South African forest plantations, the soil pest complex can contribute to serious transplant mortality immediately following re-establishment. White grubs (Scarabaeidae larvae) are one of the most important components of the soil pest complex. The control of white grubs using insecticides is highly regulated by the Forest Stewardship Council (FSC), which promotes the production of wood in an environmentally sustainable manner. An effective control measure for soil-borne pests is deltamethrin, a chemical banned by the FSC but used by the forestry industry under temporary derogation. Therefore, there is an immediate need to find effective alternative products for the control white grubs. A pot trial was undertaken to assess the effectiveness of alternative chemical and biological products to control white grub feeding on Acacia mearnsii and Eucalyptus grandis seedling roots. Four alternative products (imidacloprid, Beauveria bassiana, potassium silicate, azadirachtin) and two insecticides with known efficacy against white grubs (chlorpyrifos and deltamethrin) were evaluated for seedling performance and phytotoxicity effects, white grub control and a combination of phytotoxicity and white grub control. The products were compared to two control treatments; a positive control (white grub present, no chemical product), and a negative control (no white grub present, no chemical product). Seedlings of A. mearnsii and E. grandis treated with imidacloprid showed a significant increase in total biomass when compared to the positive control (white grub present, no chemical). Application of B. bassiana at double the prescribed rate (x2) resulted in phytotoxicity of E. grandis seedlings. This study indicates that potential alternative white grub control options exist and that pot trial evaluations are useful as an initial screening method. Further pot trial evaluation of control options is warranted as a precursor to a field trial evaluation.