Question of the Week Number 1: July 18, 2019
“My neighbor has a trumpetvine that is sending sprouts into my yard. What can I spray on them to kill them?”
You can kill individual sprouts of any broadleafed weed, trumpetvine included, by spraying them with a broadleafed weedkiller containing 2,4-D. However, with trumpetvine, there will be 10 more waiting to take the place of each one you kill.
The problem is that the mother plant, which in this case is in your neighbor’s yard, is sending out a network of roots in all directions. Your neighbor’s yard is, I’m sure, also filled with them, so your neighbors will understand your plight.
The best way of dealing with the problem is to remove the mother plant entirely, stump, main crown of roots and all. That will allow you to address any sprouts that do come up on their own terms with the herbicide or by digging them up by hand.
If for any reason you’re unable to accomplish the full removal of the neighbor’s mother plant, your other best option will be to cut a trench into the ground along the property line and install some kind of impenetrable barrier 30 to 36 inches deep. I know that sounds radical, but I don’t know of any other way to stop the spread of the roots. You could use concrete, heavy vinyl pond liner (hope that would work!), corrugated sheets of fiberglass overlapped or some similar material.
For what it’s worth, the larger-flowering and much more refined Madame Galen trumpetcreeper is far less likely to cause big problems like this. You might offer to buy your neighbor a really nice specimen to replace the wild trumpetvine that’s been causing the problems.