how to control couch grass in cotoneaster

Ah yes not an easy solution, you will have to lift sections of the cotoneaster if possible, and just weed out the grass as best you can by hand, couch grass is relatively easy to pull up the roots with a hand fork or trowel atleast. regular maintenance is the key to keeping it under control and prevent the situation from occuring in the first place. If the situation has got well out of and depending on how compact and big the contoneaster is, you may want to consider some drastic pruning or removing the plant and starting again as a last resort. Also if possible try blocking out the light the grass get by stuffing some weed control membrane or black plastic in there.