Have you pulled the dead shoot out to see if it's been chewed off, also you could try cutting the plant to find the grub and then identify it.
Sugar beet, winter wheat, OSR, should have been winter wheat this year but its spring barley.I've just looked at the picture again. Didn't realise the whole plant has been chewed off just below ground level, I thought it was the main shoot that had been nibbled.
I'm inclined to think it's leather jackets, what is the cropping history of the field????