The downside to preventive control is that a decision must be made to treat before the extent of infestation for that year is known. Preventive control is best suited to sites that have a history of grub infestation or for homeowners seeking “insurance” against grub damage.

With curative control, a short residual insecticide is applied after egg hatch. The best timing is in the last part of July or early August when grubs are still small. Grubs are much harder to control in late summer when they are full-sized. Granular products containing the active ingredients trichlorfon or carbaryl are labeled for curative control.

Confirm the presence of grubs by digging several samples with a shovel in areas that previously have been infested or in which Japanese beetle adults have been active.

Regardless of what insecticide is used, water the turf immediately after treatment to move the residues into the root zone. Use a lawn sprinkler to wet the soil to at least 1⁄2-inch depth.

Milky spore disease dusts containing a naturally occurring bacterium that infects Japanese beetle grubs can be found at some home improvement stores and lawn and garden centers. Research in other states has not shown these products to be reliable for grub control.