St. Gabriel Organics 20 lb. Milky Spore Grub Control Spreader Mix. This organic compound effectively attacks the larvae of Japanese beetles, preventing them from developing into destructive adults. Apply it with a spreader anytime from spring through fall, and it will kill grubs for 15 to 20 years. Harmless to birds, bees, beneficial insects, fish, animals, plants, and humans, this spreader mix covers 7,000 sq. ft.