It was reported on June 10th that the first Japanese Beetles have emerged for the season. This means a couple things for our lawns and landscapes.
The biggest thing to keep in mind is dealing with grubs. Japanese Beetles are one of the few white grub pests of our lawns. Consider this: if the adult beetles are emerging now from the lawns, that also means their grubs are no longer in the lawns. Therefore, this is not the time to put grub applications on the lawns. The eggs for the next set of grubs will not be laid until August at the earliest. If you want to do a preventative treatment for them, it's best to put down an application sometime in the month of July. You can find more information in this publication.
With the emergence only starting, that means the populations will only be increasing over the next couple weeks. That also means there is still more than enough time before you pull out sprayers to deal with damage from the insects. Consider this: some of the products that could be used to control the beetles, could have a negative impact on the bee population, especially if applied during flowering. The best option is to wait as long as you can tolerate after starting to see damage before your first spray. Spraying at this time reduces pesticide usage as it can help to cut out at least one treatment a year that doesn't always kill a worthwhile amount of the insects. Reapplications may still be necessary as the beetles fly around to different locations as they can travel up to 2 miles in one day. You can find information on products to use in this publication.