What other products have you applied to the same lawn? If any of the products applied kill grubs then the use of Milky Spore is a waste of time. You need live grubs to consume the Milky Spore so the stuff can multiply in the soil to kill future grubs.
There is a listing of articles about Japanese Beetle control here:
http://www.gardensalive.com/ca...
For the Milky Spore to work it must be applied at the correct time and temperature when the grubs are actively feeding. Using Milky Spore for Japanese Beetles isn't like taking an aspirin for a headache. The results from Milky Spore are seen over the long term.
