Evaluation of an application procedure for Metarhizium anisopliae in sugarcane ratoons for control of the white grub Dermolepida albohirtum

The biological control product BioCane™, containing spores of the fungal pathogen Metarhizium anisopliae isolate FI-1045, is available for soil application against the white grub Dermolepida albohirtum (Waterhouse) in sugarcane in Australia. Currently, BioCane™ granules can only be applied in plant crops, where they are distributed in a horizontal band in the planting furrows and covered with soil. Options for management of D. albohirtum would be broadened if M. anisopliae could also be effectively applied in ratoon crops. We evaluated the efficacy of spores of M. anisopliae sprayed as an aqueous suspension into two vertical slots cut into the soil in the rows of sugarcane ratoons. We were able to achieve vertical bands of spores, as determined by collecting soil samples at incremental depths and counting colonies after plating on artificial media, although spores were concentrated towards the bottom of the slot. Numbers of white grubs were reduced by treatment in some trials in comparison to untreated plots, but results were inferior to those obtained using the standard chemical insecticide, imidacloprid (Confidor®). When a low application rate of M. anisopliae was combined with bifenthrin (Talstar®), only bifenthrin was shown to contribute to efficacy with no interaction between effects of the two products, despite promising results in a previous bioassay. Application of M. anisopliae is not likely to be an economically viable treatment for sugarcane ratoons using this technique.