If, today, I dig out a dollop of soil 4 inches deep and find no grubs in it, is it safe to assume I have no grubs? Or might they be deeper than that, so can't be detected?
Ottawa County Michigan lawns and turf
Grubs overwinter just below the frozen soil and quickly return to the grass roots to feed once the ground has thawed. Checking a square foot of turf at the root level is usually adequate to see if have a problem. Low-maintenance turf will tolerate five to 10 grubs per square foot. Irrigated and high -maintenance turf can handle more. The following links should be useful:
I hope this helps,