Greetings, Tim, and thank you for your excellent question to Ask Extension/Ask a Master Gardener.

A little background information: I am a Master Gardener in Hamilton County Ohio and, along with a large group of others, I volunteer my time to answer questions from gardeners and homeowners across the state. To be certain that my response is current and accurate I have consulted several research-based sites. The links to the best of those are embedded in the response and/or included in the list of resources. If you need clarification or additional information you can reach me directly by responding to this email. I would be delighted to hear from you.

I think I can help you with your question, but the answer may not be as direct as you had hoped. There are several different beetles - including May/June beetle, Japanese beetle, and Masked Chafer - responsible for root-chomping larvae (white grubs) in Ohio, and different beetles emerge at different times. (This article from The Ohio State University Extension Ohioline can help you identify types of grubs.) To understand how to control grubs in your lawn, it is important to understand their lifecycle: they overwinter underground and emerge as adults as early as April with some species emerging as late as September. After emergence & mating, the females lay eggs underground which hatch in one to three weeks and these larvae (grubs) begin feeding, first on dead organic matter and then on roots.

As you can see, targeting insecticide application just prior to hatching may be difficult, but there are management strategies that can help you. Some are preventative while others are curative. This Lawn Care Calendar from the OSU Extension of Lake County is very helpful. If you have seen previous grub activity in your lawn it recommends a preventative “Late May application” of imidacloprid, halofenozide or Mach2 for “control through August.” It has additional advice for lawn insect control, which is curative, and other advice to maintain a strong and healthy lawn.

This article from the OSU Buckeye Yard and Garden Line (BYGL), offers management strategies (cultural and biological as well as chemical), and this article from Oklahoma State University Extension (the other OSU ;) is interesting and informative. It describes the lifecycle of beetle grubs and explains how preventative and/or curative application of insecticides can be effective. “Preventative applications typically are applied in late May and can provide season-long control of newly hatched white grubs. Larvae feed on roots of protected plants and consume a lethal dose of the insecticide. Insecticides used for preventative white grub applications include neonicotinoid products containing thiamethoxam, imidacloprid, and clothianidin and products containing the insect growth regulator, halofenozide. Preventative products are rapidly absorbed by turfgrass roots and tend to be most effective against young larvae. In general, preventative treatments are not recommended unless the area to be treated has a history of white grub infestations and is clearly demarcated.”

As always, when using lawn chemicals or insecticides, follow all package directions carefully and use all recommended personal protective equipment (PPE).

I wish you the best of luck in managing grubs in your lawn. Please feel free to contact me with any questions or comments.

Debra

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Resources about white grubs:

Identification of White Grubs in Turfgrass – Ohioline Factsheet https://ohioline.osu.edu/factsheet/hyg-2510

Lawn Care Calendar from Ohio State University Extension, Lake County https://lake.osu.edu/sites/lake/files/imce/Program_Pages/ANR/FS%20101%20Lawn%20Care%20Calendar.pdf

White Grubs (Life Cycle, emergence, chemical controls, preventative applications, ) from Oklahoma State Extension https://extension.okstate.edu/programs/turfgrass-science/educational-materials/white-grubs.html

White Grub Management https://bygl.osu.edu/node/855 Advice for keeping turfgrass healthy; dethatching.

Turfgrass Team Times (An excellent resource for lawn care from OSU Extension) https://bygl.osu.edu/index.php/taxonomy/term/1580

The Great Grub Switcheroo https://bygl.osu.edu/node/370