Question
I moved into a new home last May. Sometime in July I found that I had a very serious grub problem over half of my lawn which is about a half acre.  The grass can be lifted easily, like a carpet.  I put a grub control product on the lawn in late September but the grubs were still visible up until the winter.  I am thinking of replacing the whole lawn but I would rather not do that since it is very expensive.  Is their any other remedy.  I REALLY NEED HELP! Thank you in advance.

Answer
Good afternoon Dom:
White grubs are the most serious and destructive insect pest in the lawn. The extent of grub damage may vary from year to year. Grubs are white in color, with a characteristic "C" shape body when found in the soil feeding on lawn roots. Grubs are the larval stage of beetles.
The most common grub specie is the annual white grub, of which the adult is a tan chafer beetle. Eggs are laid in the soil in mid-summer, usually on well-watered lawns in full sun, often near pavement. Damage from annual white grubs in cool season grass lawns typically starts in mid August and may continue until early October. Other species may damage lawns, but usually are not as common as annual white grub. Control of these species is the same as for annual white grub. The white grub (May or June beetle), for example, typically has a 3-year life cycle, meaning it could potentially damage lawns throughout the season. Japanese beetle grubs can also occur, with timing very similar to annual white grub. Adult Japanese beetles are serious defoliators of many ornamental plants.
Since grubs feed on the roots of lawn grasses, damage will appear as browning of the lawn. Of course this also could be due to problems such as drought, poor soil, and diseases. Grubs are easy to find, as you have done, by lifting sod in damaged areas and checking the root zone for the whitish grubs. Don't treat for grubs that don't exist! Skunks and raccoons may tear up lawns in search of grubs, even when grub numbers are relatively low. Typically a population of about 8 to 12 grubs per square foot causes lawn damage that requires control; whereas lower populations may not damage the grass, they may however attract skunks and raccoons.
Lawns showing damage from grubs may be treated with an insecticide. Insecticides available for homeowners include diazinon (25% EC [liquid] or 5% granular); trichlorfon (Dylox) (6.2% granular); bendiocarb (Intercept), halofenozide (GrubBGon, GrubEx), or imidacloprid (Merit, formerly GrubEx) for control of white grubs. Heterorhabditis bacteriophora nematode is an example of an alternative product for white grub control that is available.
For all products, read and follow all label directions, then apply to damaged areas only. Water the insecticide into the soil immediately. If treating a large area, stop after a portion has been treated and water the material in, then complete the rest of the lawn area needing treatment. Only treat in and around affected areas; grubs may only be in a small part of the lawn. Imidacloprid and halofenozide are suggested to be applied before grub damage appears. An example of a way to use these products would be to apply in July to irrigated lawns that are surrounded by dry lawns, especially when adult beetle flight is high in areas with a history of grub damage.
Spring treatment for annual white grub is not suggested since the grubs feed for a short period of time in spring and are reaching maturity, thus are not controlled easily. In addition, turfgrasses are actively growing at that time so usually don't show damage.
Applying pesticides for control of anticipated grub populations is not recommended. However, in  your case where adult activity has been observed or perennial infestations have occurred, preventive applications may be warranted. Currently, imidacloprid (=Merit), isofenphos (=Oftanol) and isazophos (=Triumph) are the only registered products which seem to have extended activity. In field trials, imidacloprid and isofenphos generally perform best when applied before mid-August, or when white grub egg laying is underway.
You have indicated that your application of insecticide occurred in late September. Next year begin your insecticide application in July and water it in immediately. Depending upon the seriousness of the grub infestation and the type of grass you have, the lawn may recover in the spring or complete renovation may be necessary. Wait and see what happens then make up your mind as to what you want to do. If you decide on renovation let me know and I will guide you. Remember that it is best to perform renovation in early fall.
Have a good lawn.
Floyd McMahon