Last fall I started to see a grub infestation in my lawn. I did use Scott's Grub X in the areas that were obvious to the problem. My understanding is that the problem is yearly and actually keeps increasing if not treated annually. My question is I have 5 acres of lawn, so what product can I use that is effective on all five acres. I need something that you can buy to handle five acres and doesn't totally cost a fortune. Thank you for your help.
Be positive that your lawn has a 'grub problem'. It is normal (even beneficial) to have some grubs in the lawn. It takes about 12 per square foot to actually damage a lawn--and usually needs dry weather, too. Most of the time, grass roots grow faster than grubs eat. It is rare for grubs to be causing dead lawn. Fungal disease and other causes are more common. Though, irrigated lawns do tend to attract beetles when they lay eggs, which leads to lots of grubs.
Grubs are immature beetles, often Japanese beetles, which emerge in early summer and can fly off anywhere. No reason to stick around on your lawn. So, build up is not a problem. Here's our webpage on grubs: https://extension.umd.edu/hgic/grubs-lawns
We would recommend that you only use grub control when you have a problem, and apply it only to affected areas, just as you did. We know of no inexpensive grub control products. Annual application is not necessary. Also, since grub control is a pesticides that is toxic to non-target organisms that you want in your healthy turf, it's best to avoid it whenever possible.