Asparagus Beetle-burning old stems

I had terrible asparagus beetle last year (until I discovered pyrethrum spray). RHS advises burning the old stems to destroy the overwintered beetles which I think live just below the soil surface in the roots.

https://www.rhs.org.uk/advice/grow-your-own/vegetables/asparagus

Has anyone tried this? I haven't yet cut down my old ferns so was thinking of chopping them down to about 10cm above ground level and on a dry still day use a blowtorch to try to burn the stems tackling each plant individually. Am I mad???!! Or more importantly am I going to kill the asparagus I tended from seed four years ago?

I think using a blowtorch on the existing stems would damage the roots, so perhaps carefully forking over the soil would expose the beetles for the birds to eat.

Thanks for the advice! I've seen some blogs (usually American) where they set fire to the whole ferns but I'll go for the safer advice options you suggest.

Perhaps cut the stems,then turn the soil ,then a quick blast from the blow torch,the birds could then have roasted beetles