To be a problem, according to the turf grass people at Michigan State, Ohio State, and Purdue, your grub population would need to be in the area of 10 per square foot, 5 or less per square foot would not be a problem. To determine that population dig out a one square foot section of your turf, or take a spade and cut in a :_: and fold the turf back and then count the wee buggers there.
Milky Spore Disease, "Bacillus popilliae", is present in most soils already, just not enough and it can take some time to show spectacular results and since it is a passsive means of control, the grubs must ingest it, many people think it does not work. Parasitic nematodes can also be used IF there is a real grub problem.
For most people grubs are not a real problem, and do not need as much control as the people that sell control products want you to believe.

Grubs were more than 10 per foot. More like 20 per foot. Damage was total dead grass. When should I apply parasitic nematodes? In the fall and spring? I have had grubs for 10 yrs. But this invasion was massive. Also, what should I apply now for my fall fertilizer? I have been using SBM, now what? Grass seed is just poping their hair up. I don't what to smother them. Did I do much damage to my organic lawn using the Grub killer? Thanks