I need some help to ID this weed on my rooftop and what can I use to get rid of them. I've tried pulling them but the stem would break off from the roots.
It's a species of Wigandia, maybe Wigandia caracasana, and is possibly native in your part of Mexico. In some other countries it is regarded as an ornamental, though admittedly it is a rather untidy plant. I once grew one and it reached about 4 metres high in under 5 years.
I am not sure how you would kill it. Most woody plants can be controlled by curtting them off close to the ground and immediately pouring some concentrated glyphosate ('Roundup', etc) onto the cut stump. You may need to wait 2-4 weeks to see the effect.
Thanks Tony, searched for wigandia and it seems to match this plants. Dunno how they invaded my rooftop since I don't have any on my garden. I guess some neighbor had one and it's seeds spread thru the neighborhood.
I bought some glyphosate and it works wonder on them. I sprayed the smaller ones with diluted glyphosate and they dry up and die within a week. As for the mature plants I did cut them and poured glyphosate, after a month it seems to have worked.