In article , Steve Warren @ The UK
Speedtrap Guide writes
Hi
Last year was the first time I decided to grow cucumbers in the greenhouse,
in fact it was the first time growing them.

The plants start off very well and grow some crop, we have done very well so
far with the ones that are ready.
However last year and now this year the leaves start to get mouldy spots on
them and then start to yellow at the same time the young cucumbers start to
yellow and die..

That could be cucumber mosaic virus. If so, you would see a criss-cross
'diamonds' pattern forming in the leaves as the veins become infected.
The virus can be transmitted to other plants by aphids, or by handling,
so it is best to remove and burn affected plants. The cause can be due
to buying in uncertified stock, or it can be a build up of disease in
the greenhouse.
--
Alan & Joan Gould - North Lincs.