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My winter lettuces (winter density and a winter type iceberg and a mixed winter type of leaves) were doing really well. I sowed and planted them in the greenhouse at the end of September. One by one the winter density and the iceberg type started to develop mold on their leaves. I tried picking off the affected leaves but it got worse. I planted the  winter iceberg and winter density in a used tomato grow bag. I kept the greenhouse door shut as I felt it would be too cold and of course it was too cold for the auto window to open. The mixed leaves are fine and not affected by mold.
Can anyone offer some ideas on how I can prevent this happening next year?

Duke :)

Grey mould is a real pig... the best solution is actually ventilation... open the doors once the sun is well up to "dry" out the greenhouse... the actual cold around midday even down to minus five won't upset Winter lettuce if it is "dry"

I grew winter density last year and they were OK but not brilliant.  This year I am growing Valdor which is doing much better and looks the best winter lettuce I have grown to date.  I have had 2 plants with the same type mould you mentioned.  After removing them leaves I have had no more problems... so far (touch wood).  I do not know the cause but am guessing it could be to do with the extreme cold temperatures.

Damp not cold is the real issue
:-\

Thanks for your suggestions...
Having thought about it, there is a lot of condensation in the greenhouse. I never thought that opening the greenhouse would be okay during day in the winter months. I should have known that winter lettuce would be okay *doh* silly me.

Growing veg is such a learning curve !

Duke :)

OMG  :o :o You've just reminded me that my winter lettuce (outside but in a fleece tunnel) will now be under a foot of snow!!