Being new to this gardening lark (at least in this country), the Head
Gardener and I thought we would plant five varieties of potato to see
how they fare. Our allotment in SW London was in a hell of state when
we got it last year, and potatoes would be a good way of cleaning the
soil too. So we prepared the beds with plenty of manure, chitted the
potatoes and planted them during April. Earlies were Epicure and
Ballydoon, second earlies were Kestrel and Saxon, and Main Crop were
Ratte.

Having had very acceptable results so far with the earlies and second
earlies, we were keen to know how the Rattes were getting on, and
being unable to contain our curiosity any longer, we lifted one plant
this morning. They were sown on 18 April (15 weeks ago), and we
weren't sure when we should harvest them. The haulms withered some
weeks ago, but our books indicate that main crop potatoes should not
be lifted until Sept/Oct, or 22 weeks, if being stored for future use
(we still have plenty of the second earlies left for immediate
eating).

Anyway, upon cleaning the potatoes, we were a bit dismayed to find
that something had been nibbling away at a few of them. All damage
was on the surface to about 1/4 inch deep, and didn't affect the rest
of the potato. Consulting our books and the internet, we couldn't
establish what it might be. Slugs would be unlikely for Ratte,
especially with this warm, relatively dry weather we've been having in
SE England, and so early in the year.

When we were digging the potatoes we came across a monster chafer
grub. Clearly it had to have been eating something in the ground, but
I can find no reference to chafer grubs attacking potatoes.

What might be eating our Rattes? Would it be the chafer grub? If so,
and on the basis that where there is one chafer grub, there are likely
to be more (we have come across quite a few in our soil), what can we
do about it? Should we lift the lot? (Presumably the tubers will
have stopped growing when the haulms withered away.)

All advice would be greatly appreciated.