Some weeds and grasses build up a tolerance from certain chemicals being sprayed on. Just don't work as they used to. Reason why you should alternate/rotate herbicides and see what is working for you in YOUR yard.I saw a video on Tenacity last night. It did not do well with a lot of weeds and grasses it should have. Good luck.
Don't think so. Lots of St. Aug in Florida.So St. Augustine is Fescue from what I am reading online
One season I sprayed pre-emergent every month. Still had weeds. Prodiamine is a huge favorite pre spray in my area. Weeds don't die. They get stunted till next season.Getting a good pre-emergent down a couple times a year will help keep weeds and unwanted grasses down. The seeds come in on the wind. That reminds me it is time to do my lawn again before the winter POA starts to take off in a couple weeks.