Squashes died on manure heep

I have recently planted some sweet dumpling squashes on top of a well rotted manure heep through a membrane. However I have just been up to the allotment and all of my squashes have wilted and are past hope.  I have looked at the stem bases and there are loads of tiny white worms which I assume have caused the problem.  Does anyone if they are the poblem, or know what these worms are and how to avoid the problem in the future?

 Many thanks

Shed, you do not say where you are, but I always protect my squashes with cloches for the month of June against the weather. I have not lost any so far.