Ruud,
As Daikon are part of Mooli/Radish family, sounds from the description as if they have been attacked by Cabbage Root Fly. White maggots! Unless anyone knows different, no permitted chemical treatment. All that's recommended by RHS is collars of carpet, fleece, whatever to prevent females from laying eggs.
Sorry, not a great gardener with veggies, hope someone else can suggest something more encouraging.