When should I apply a preventive type insecticide to control white grubs in the lawn?

FAQ
Question: 

When should I apply a preventive type insecticide to control white grubs in the lawn?

Answer: 

White grub populations and damage to lawns vary greatly from year to year and place to place, even varying from spot to spot within the same lawn due to variations in beetle numbers, weather, turfgrass vigor, soil conditions, and other factors. 

There are basically three approaches to grub management in the home lawn.  One approach is to apply a preventive insecticide to the lawn on an annual basis.  The second approach is to wait and see and apply a curative insecticide only when damage symptoms or signs of a grub infestation appear.  The final approach is to do nothing (in regards to insecticides) and repair damaged lawn areas when grub damage occurs. 

Late June to early August is the best time to apply a preventive insecticide.  Several insecticides are available to commercial applicators for prevention of white grubs.  Preventive insecticides available to homeowners include imidacloprid (Merit®, Grub-Ex®) and halofenozide (Mach 2®, Grub-B-Gon®).  When using insecticides, carefully read and follow label directions.