I know there is a deep horizontal root system to the Spanish "Bayonets I removed. I was told by a certified technician for Florida that Prametol would eventually kill the root system but needed daily watering in. We did not get rain for the first two weeks I used it and I faithfully watered it in everyday for 2 hours letting my pump run all the time. It was hot and I would see new growths sticking up and knew I lost the battle. It was too much to water everyday and I didn't appreciate the increase in the electric bill and see it was not working. I now just hit the new growth with Roundup knowing it will kill only that much but it makes life easier. The Bayonets won the war.
I bought this after talking to a technical expert for this area-Florida-to kill Spanish Bayonet roots deep below 4 to 6 inches of broken tile. It has to be watered in daily which I have done for 2 weeks straight if it did not rain. I have had 4 new growths coming up from the tile. I was warned it would take 2 to 3 weeks but with no rain and 95 degree weather I cannot keep it up with the water pump constantly running for 1 to 2 hours. The bayonets came up today so I guess they won the war.