I have what looks like a fine crop of radish (rudi) untill I cut them open
and they have brown coloured runs in them where a small white grub is
burrowing. There is no outward sign of leaf wilt or discolouring and they
are growing in a raised kitchin garden(like a box on legs) 30 inches high,
in compost. Any ideas what this pest is and how to treat it?