How to get rid of mason wasp?
Hi, I'm an entomologist from Cornell University. I have a few perspectives on this.
1. If these are true mason wasps (they use mud to construct nests and are usually solitary, not social) they are beneficial and why get rid of them? Not likely to sting. There are many types of wasps and bees that will use holes.
2. If there are mud pots, you can physically remove them. If they are using holes created by another species, you can use wood filler to fill the holes after scraping out any mud or debris that they have put in there.
3. Any OTC wasp and bee spray will kill them, but we never advocate for the use of pesticides, especially when a beneficial insect is involved. Physical removal and sealing up the holes with wood filler (Minwax High Performance wood filler for example http://www.homedepot.com/p/Minwax-12-oz-High-Performance-Wood-Filler-21600/100376245) will be the most permanent solution.
I hope this information helps!