Picture posting is enabled for all :)
I had them for the first time last year, I was horrified and not a little disgusted to find all these little spikes sticking out of the spears....I cut everything right down to under the soil, and inspected 3 times a day (yes, easy for me, garden not lottie). It took about a fortnight till I stopped finding beetles, but was clear for the rest of the year. I've already started inspecting the bed so they don't get hold again this year. Someone may come along with a chemical solution, but I garden organically...
What did you inspect after cutting them down - did you check the new bits as they grew, or did you go under the earth to find the beetles?