Allelopathy from Virginia Creeper?

Next door have a climber that is either a Virginia Creeper or Boston Ivy, I am not sure which. It gets colourful foliage in autumn, and does provide us both with privacy, though it tends to invade a bit. Not a problem now as it is nearly autumn and it will soon look very pretty and then lose its leaves and die back a bit.

My Morning Glory (Grandpa Ott) has climbed so high that it started to twine around and share airspace with the Virginia Creeper/Boston Ivy. But it seemed to stop growing when it met the Creeper, and the past two days I have noticed that it has stopped producing flowers, though in other parts of my garden Grandpa Ott is still flowering as prolifically as before. It could also be due to me removing the yellowing lower leaves two days ago. I did wonder if there is something in yellowing leaves that the plant uses, or if they are not necessary as they won't be photosynthesising without chlorophyll?

Maybe I will climb up there and try to extricate the Morning Glory from the Creeper and see if that brings flowers back. I am wondering if allelopathy can affect plants even though they don't share soil, and if these Creepers are known to have this affect?

 

I climbed up and extricated the Morning Glory. I am not sure if I damaged it doing that, which seems unlikely as it is like a thick rope of many strands all coiled around each other, but the end parts are drooping and dead, and not producing flowers.

I am not sure what happened to it, as it had stopped growing a long time ago and then stopped producing flowers for two days. Maybe it had reached its maximum height, and its flowering ends fell down rather than try to climb any further. It might not have had anything to do with the Creeper.

It was producing its flowers at the top, so with a bit of luck it might start producing flowers lower down where its leaves are still healthy.

I just noticed a bright purple Morning Glory flower, and one of its leaves, high up on the Virginia Creeper (it is a Virginia Creeper, it has separated leaves), so some of it is still ok.