I recently emailed Jeyes to ask if it can be used as a biocide to kill moss off instead of using the manufacturers expensive stuff. Apparently it killed everything off at one time but in recent years they have had to weaken it to comply with EU regulations. There answer was no, it doesn't so I don't think it will kill this triffid off. At least try a good weed killer but as Flinneyman say's take a brick out and remove every trace of root or it will be back to haunt you, preferably after using weed killer.
Anyone old enough to remember the film about Triffids taking over the world?