Question
Just noticed a wasp digging a hole in the base of our 2 yr. old Ash tree!  Do they do this?

Answer
Yes there are wasps  that will tunnel in the ground or under the roots of trees making nests. If there is a wound in the trunk and decay they can even make their nests in hollow trees.

If ground-nesting bees and wasps can be ignored and their tunnels tolerated, do so since they are valuable in agricultural production and helpful by controlling pests in nature. If nests are in locations undesirable and stinging is a great possibility, control is justified. During the day, carefully watch where the nest entrances are located. After dark, tunnels and the surrounding area can be treated with dusts of carbaryl (Sevin), bendiocarb (Ficam D) or diazinon when the nest is in the ground. Other lawn and garden insecticide sprays can also be used, but dusts have the advantage of not soaking into the soil. Those who are allergic to bee stings, should contact a licensed, professional pest control operator to perform the control job.