The good news is that we don’t have a lot of folks that have root maggots. Just the thought of them gives people the heebie-jeebies. They mainly show up in vegetable gardens. The main cause of root maggot infestation is adding animal manure that has not has not been fully composted. If you have access to raw/un-composted manure, you should look into installing manure tubes, also called worm tube and composting tubes. They are 4 to 6 inch PVC pipe that are 4 to 6 foot long. Drill several .5 to 1 inch holes in the bottom 18 inches. Burry the pipe(s) about 2 to 3 feet. Mix some soil with the raw manure and put it in the pipe. These can also be used for other composting operations. The manure composts and releases slowly. This will somewhat isolate any root maggot larva.
Unfortunately there just isn’t a good way to get rid of root maggots in a timely manner. Beneficial nematodes show good promise but they are a long term solution to a root maggot problem.