Do yourself a favor and visit a John Deere/ Lesco branch for your commercial products.
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Granular grub products are better for homeowners because they don't usually have the spray equipment necessary to get enough chemical mixture volume into the soil. Merit is one of the best but there are others such as Mach 5, etc., that will do a great job.
Milky spore is a bacteria that occurs naturally in the soil but in small amounts. If you apply it to your soil it does take weeks, months, or more to be active throughout. It CAN last for years but it's best to replenish it also over time.