Killing a Wasp Nest Under My Yacon

Yesterday I decided to tackle weeding my yacon patch, which was very overgrown with tall grasses etc. As I was pulling clumps out, I noticed a wasp darting among the plants, low to the ground. Figured I'd dispatch it, so stomped on it in my boots, pressing it into the ground near the base of one clump of yacon. Instantly there were several wasps circling my boot! I'm allergic! <Rapid exit, stage right......>

Once they'd calmed down, I continued weeding, avoiding getting close to that particular clump (fortunately at one end of the patch), meanwhile keeping an eye on it to see what I could observe. Every now and then a wasp would come or go, seemingly crawling into the dirt under a particular yacon tuber, or behind it in the middle of the clump. I figured there must be a small nest being developed there under the plant - small based upon the limited number of wasps in evidence.

Now, I don't normally rush about killing things in the garden - every creature has it's place in a balanced ecosystem, and the odd wasp helping itself to any caterpillars on my plants is not unwelcome. I do, however, draw the line at paper, German or common wasps building nests in my garden - allowing it would encourage their proliferation (they pose a risk to native species), and also greatly increases the risk of myself or one of the other females of the family (all allergic, though the guys aren't) being stung.  

This evening I asked my boarder (only other person home) whether he's allergic (no) and how brave he was feeling. After considering a number of options, I had decided to try the boiling, soapy water method - I didn't mind killing that one plant, but did not want to pour any poisons into the soil of my edible garden, and could not source the bait you can put on meat and have the wasps take back to their nest and feed their young, killing them all. He was happy to help, but not quite convinced there was a nest there, he poked around a bit, then pulled up part of the plant, which exposed the top of the, as expected, fairly new nest - about softball sized at the top. Needless to say, the wasps were not happy! <Both exit stage right!>

I put a large pot of water on to boil, then added a generous amount of dish soap. He took the pot and poured it carefully but rapidly over the nest. It completely dissolved the nest instantly, killing everything. No live wasps came out. A half hour or so later I saw one late returner buzzing about looking for the nest, without success. This pic is the hole under the plant where the nest was:

So, no more wasp nest. Now I can continue tidying up that patch, install a new side as the old one has rotted through it's stakes, given them a dressing of some compost and mulch, and plant a flower border along the side. Hmmmm...what shall it be? Cornflowers? Dahlias? Calendula? Zinnias? Cosmos? Choices, choices!