When it comes to treating for grubs, you have 2 options. However, the best method would be to apply PREVENTIVE insecticides in June/July that will prevent grub damage in fall of 2018 and spring of 2019. The other method is applying CURATIVE insecticides in late August to September. This method is not as effective as the preventive compounds in reducing grub numbers. Here is a link to wonderful publication that will explain everything very well, http://msue.anr.msu.edu/news/how_to_choose_and_when_to_apply_grub_control_products_for_your_lawn .
Please do not hesitate to call the Fayette County Extension Office if you have any further questions or concerns, (859) 257-5582. Thanks!