Milky spore should be applied in the late summer or fall. Success is soil type and pH dependant, and may take 2 to 5 years before you see a substantial change in the grub population (the average is 3 years). In the meantime, put away your traps, which attract more beetles into your yard.

Beetle damage may not be indicitive of the grub problem you have. If you have more than your fair share of plants that JB love, or you are luring them into your yard, you will have all sorts of damage from the adults but may not have a grub infestation. Do a grub scout of a sunny portion of your lawn to determine the population.

If your JB issue is from neighboring grub infestations, your application of milky spore is a waste of time and money.