Here is a quote:
Because it is an aggressive twiner, morning glory can produce a significant amount of foliage (i.e., vertically, upon shrubs, trees or structures) on a small amount of open ground; the roots and rhizomes will be much more laterally extensive. Vegetative growth produces sugars (from photosynthesis), which feed the rhizome network, creating a vast reservoir of energy for continuing growth or regrowth. This is why cutting the top off of a morning glory hardly slows it down.
Control is simple in theory, but seldom achieved. Calystegia is ultimately not very tolerant of heavy shade, infertile soil nor extended drought and so, tends to favour moist, rich ground in sun or semi-shade. However, because it usually has a huge root and rhizome network with plenty of reserves, it can tolerate horrible conditions for a long time before it starts to suffer. For example, it often emerges from the ground in heavy shade, under shrubs, or through stony, dry soil, but eventually makes its way into sun. Keeping the morning glory restricted to the sub-optimal areas by regularly and continually cutting off photosynthetic tissues in more optimal areas will eventually weaken it. Unfortunately, while you mght be controlling its growth, your next door neighbour may not. In other words, there’s usually a monster on the other side of the fence, waiting for you to lower your guard. However, if you can involve everyone in the process, the chances for success are increased.
The most effective approach to control is exclusion of light. It will usually take less than a year to completely kill off morning glory if it is prevented (completely!) from seeing the light of day. There are various ways to accomplish this, the most effective being covering the ground with carpet, cardboard, layers of newspaper or turf. Notwithstanding European chafer infestations, few things are as good looking while effectively starving out perennial weeds as a healthy stand of turfgrass. Together with repeated cutting where new shoots emerge, the light exclusion method is very effective.
Here is the source