You can find beneficial nematodes on line. There is some question, however, if they can survive the shipping and they can be fairly expensive. Milky Spore Disease, now "Paenibacillus popilliae" formerly "Bacillus papillae", may be a better choice, next year.
Is it necessary to do anything at all? Do you have more than 5 grubs per square foot?

Yes, I'd say there is more than 5 grubs per sq ft. I'd say at least 8-10. Some patches of lawn basically rolled like a carpet while aerating. Also, japanese beetles hit pretty hard the roses near my lawn this year (don't japanese beetles start as a grub too?)

thanks.

in my MI ... the grubs are the beetles ...

i was never impressed with nems.. as a solution .... BUT!!!! ... i never tried them ....

with bugs like this... the populations ebb and flow over the years .... is this the first time you have noticed them????

ken

Yes first time I notice them. Lawn is about 4 years old.

Japanese beetles do come from some of the grubs found in soils, as do other members of the scarab beetle family.
However, a large number of Japanese beetles in your garden does not necessarily equal a large number of grubs in the soil. If there are large numbers of grubs in the soil timing of controls is essential since some work best when the grubs are fairly young while others might work on older and larger grubs.
Applying Milky Spore Disease is best done in late July to early August (before the grubs hatch from the eggs laid) so it is in place when the grubs hatch. Milky Spore Disease is a passive method of control, the grubs must find and ingest the bacterium, which is why some "authorities" consider it to be not very effective. MSD does not immediately kill, but it also does not kill beneficial soil organisms.
I find little information about when to apply beneficial nematodes except one reference to temperatures in the 45 to 105 range. Many sources (sellers) also suggest applying them every two weeks, which can get to be very expensive.