Pot trial 2: refined screening of alternative chemical and biological products against larvae of Schizonycha affinis (Coleoptera: Scarabaeidae) on wattle and eucalypt seedlings

Sivparsad BJ, Germishuizen I
Publication Type
Technical Note
Publication Year
TN 03-2018

White grubs can contribute to serious transplant mortality immediately following re-establishment. Registered insecticide treatments of deltamethrin and imidacloprid have been deemed highly hazardous and their use is restricted by the Forest Stewardship Council (FSC). Therefore, there is an immediate need to find effective alternative products for the control of white grubs. A previous pot trial was conducted to screen a broad range of alternative chemical and biological products for the control of white grubs. The study showed that treatment with alternative chemical (imidacloprid +clothianidin tablets) and biological (Beauveria brongniartii, azadirachtin, potassium silicate) products protected seedlings from white grub damage and could be used as a viable control alternative. However, further pot and field trial evaluations were warranted to confirm product recommendations. To this end, the pot trial was repeated to include the screening of a refined list of the best performing alternative chemical and biological products against white grubs on Acacia mearnsii and Eucalyptus grandis seedlings. Three alternative biological options (B. brongniartii, azadirachtin, and potassium silicate), two alternative chemical control options (clothianidin, and imidacloprid + clothianidin tablets) and three insecticides with known efficacy (deltamethrin, imidacloprid liquid and imidacloprid tablets) were evaluated for the control of Schizonycha affinis on A. mearnsii and E. grandis seedlings. All treatment combinations 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). Overall, treatment with imidacloprid tablets and liquid (registered products), clothianidin (a chemical alternative) and B. brongniartii (a biological alternative) were significantly superior to all other products resulting in increased total biomass and biomass index of eucalypt and black wattle seedlings. Treatment with imidacloprid + clothianidin tablets resulted in a significantly greater total biomass and biomass index for eucalypt seedlings only. Biological products containing potassium silicate and azadirachtin did not reduce white grub damage of seedlings. Taken together, results indicate that potential alternative chemical (clothianidin) and biological (B. brongniartii) control options exist, and further field trial evaluations are currently underway to validate product recommendations.