wireworm eating onions

[sawfish]

I planted out some onions I've grown from seed a couple of weeks ago and they seem to be doing OK although they haven't started bulbing up yet.

I noticed the other day that several have toppled over because of gnawing at the base of the leaves, luckily I have replacements but on replacing I found orange wireworms in the earth at the base of the gnawed ones. What can I do to rid myself of these? Its only on a couple of beds.

[sawfish]

[Ishard]

Soot and spread it liberally but not touching the plants.