Although lasting control of high grub populations (>10/ft2) have been reported within 1-3 years after applications of a commercial preparation, control in the field has been variable. Researchers at the University of Kentucky tested commercial preparations to examine causes of this variability. Laboratory tests using Doom showed that this formulation was moderately infective with 39-44% of grubs becoming infested. Large scale field tests conducted in plots with pre-existing Japanese beetle infestations failed to link milky disease to lower grub populations during the 3 and a half year study. Small plots, artificially infested with grubs, and laced with milky disease according to manufacturer recommendations also failed to reveal disease symptoms over a 17 month period. Finally, grubs infected with milky disease were found to consume the same quantity of roots as uninfected grubs.
In summary, milky spore preparations were found to be ineffective when used according to label directions in the field. Reports of success by previous researchers were limited to very high infestations of grubs where other stresses may have increased their susceptibility to diseases. The only good news to report is that the commercially produced milky disease spores were able to infect grubs in the laboratory. The challenge that remains is to figure out how to get it to work in the field.
Redmond, C. T. and D. A. Potter. 1995. Lack of efficacy of in-vivo and putatively in-vitro produced
Bacillus popilliae against field populations of Japanese beetle (Coleoptera: Scarabaeidae) grubs in Kentucky. J.
Econ. Entomol. 88: 846-854.