Time to consult Dr DG Hessayon via his most excellent publication, The New Vegetable and Herb Expert -a somewhat reassuring title don't you think? Dr Hessayon has a 3-page spread devoted to 'Cucurbit troubles' - a list of 23 separate things to concern you.
I must say that these lists of things that can go wrong used to put me right off growing vegetables. It all seemed too hard , even 'dangerous'. Now I just ignore most things and let things get on with growing. I now only consult Dr Hessayon when I think something really is an issue and when I really don't know what it was. This is one of those occasions.
Of the list of 23 'problems', number 14 - the 'withering of young fruit' seems to be the best description. From here I directly quote Dr Hessayon page 55.
Cucumbers and marrows stop growing when they are only a few inches long and withering spreads back from the tip. Unfortunately there are many possible causes such as draughts, heavy pruning and the use of fresh farmyard manure. The most likely reason is faulty root action due to poor drainage, overwatering or poor soil preparation. The secret is to maintain steady growth by careful watering. If withering of young fruit does take place, remove damaged fruit and spray with foliar feed.
So, fruit removed as instructed I consider the causes:
- Draught - possibly, I have no fence line to protect my crops.
- Heavy pruning - possibly, I did tidy up the plant by removing their wind burnt leaves.
- Fresh farmyard manure - I don't think this is the cause. The sheep pooh from under the shearing shed is 'aged' and unlikely to have burnt the plant.
- Faulty root action due to poor drainage, overwatering or poor soil preparation - A probable cause - not the overwatering aspect - I suspect that my hastily built garden beds would be classified as 'poor soil preparation'. I suspect that you couldn't call it soil at all at present - just layers of cardboard, grass clippings and sheep manure.