"Brian Watson" wrote...
My daughter planted a row of turnips and only the left-hand 50% have come
through to show some early leaf growth - the rest, nothing at all.

They don't use weedkillers so nothing has been applied by them to the
surface to prevent germination.

Any ideas what could cause such a weird effect?

I'll take a bet it's Flea Beatle. Very bad this year, despite dusting all
brassicas with Derris Dust as soon as the seedlings appear we have still
lost half out Turnips and a lot of Radishes with the remainder looking like
lace as do our planted out cabbages.
If you have never seen it look for tiny pin head sized little shiny black
dots that jump if you try to touch them.

--
Regards
Bob Hobden
17mls W. of London.UK