couch grass

Would covering the area with sheeting, weed suppressant stuff etc... for the next 5 or 6 months help kill this?

In my humble experience, one of the positives about couch grass is that it does respond well to chemical treatment.

To clear the worst of my plots, I hacked the stuff down with a slasher and used a watering can to apply glyphosate, carefully marking where I was in order that it was completely covered. I`m not sure about strimming the grass short before spraying - I suspect that the more leaf area is available, the more likely the whole plant is to recive a lethal dose.

Then leave it to die. 

Then when the stragglers come through dose it again.  You`ll also take care of the first flush of new weeds from seeds here.

Then I dug and sowed a dense green manure (mustard) which was dug in and the plot covered until the next spring.

I didn`t dig out all the (should be dead) roots out. I figured that it`s all organic matter and that if I was prepared to do that, I may as well not have bothered with the weedkiller.

It`s not come back apart from the strays from the edges.

As said before, it`s best to attack it in spring when it`s actively growing.

Will