Answer: Elm trees are susceptible to emerald ash borers and the holes you see on the trunks and branches of the tree are signs of borer infestation. These pests are extremely difficult to control, although with small trees it is possible to skewer the worms that are hiding inside the holes with a straightened out paperclip. I doubt that's something you'll be able to do with such large trees, though. The grubs you're finding in the soil are not the same grubs as are making homes in your elm trees. It might be worth your while to hire an arborist to come out and inspect your trees so you'll know just how extensive the damage is/will become. You might also contact your local cooperative extension office for their recommendations about treatment and control. Sometimes extension agents and/or trained Master Gardeners will make house calls. It won't hurt to ask. Contact Arizona State University Cooperative Extension, 4210 N Campbell Ave, Tucson - (520) 626-5161
Best wishes with your trees.
Q&A Library Searching Tips