What did you spray? Did the label say it was for St Augustine or just for southern lawns? Most of the southern lawns types will kill St Augustine unless it says it is specifically for St Augustine. It really is a shame the way they are allowed to market those bags of herbicide.

Did the herbicide specify to not spray if the temperatures were expected to be higher than 85 degrees F? Many do. Summer in the south is a bad time to spray almost anything.

Where do you live?

Do you know if you have the Floratam variety of St Aug?

And I may as well ask how you currently water. How frequently and for how long?

It was an already mixed version of the weed killer and is specifically for St Augustine lawns. I live in South Florida.

I treated the lawn around 8:30-9am and temps were in 80s that day with a forecast of afternoon rain.

It's rainy season so trying not to overwater but when I do water the lawn, it's for 15 minutes each zone.

I am heartbroken over this. I just bought a house and this is my first lawn. I asked every question and read product labels so I was trying to do the right thing to help it grow and now I'm afraid I have killed it.

The product by the way was Bayer Southern Weed Killer For Lawns. It is specifically made for St Augustine lawns.

Here is a link to the label for that product.

That label specifically says not to use it on the Floratam variety of St Augustine. If that is what you have, then you are in trouble. If not, then the grass should recover after a brief yellowing. This time of year you should not use a chemical fertilizer on St Augustine. You may; however, use all the organic fertilizer you want without fear of doing any further damage. It will help with greening when the grass bounces back. The organic fertilizer I like is plain alfalfa pellets (rabbit chow). Apply at a rate of 20 pounds per 1,000 square feet. Although the alfalfa effect begins immediately by feeding the microbes in the soil/sand, it takes a full 3 weeks to see the improvement in the lawn.

The label also says not to apply if the temp is going to be 90 degrees. You did not have that situation, but so many people do I just want to reemphasize the point. Although the label says 90 degrees, the common homeowner should not apply above 85 degrees. You're just asking for problems.

It sounds like you applied over the entire lawn. One of the reasons to use a liquid like this is so you can just spot spray the weeds and not have to worry about messing up the entire lawn. If you had only spot sprayed your feeling of heartbreak over this would be tempered considerably. If this goes bad for you, it's going to be very bad.

Here's a summary of how to make St Aug grow.

Water deeply once a week. This is slightly variable, and we're hearing from the Florida crowd this year. If you are watering more than 2x per week or more than every 5 days, you should back off. I realize you're probably getting rain every day, so you really don't need to be adding more water. Once the rainy season ends, with temps in the 80s, you should be able to go 10 days to 2 weeks without watering. This depends on your soil (sand), heat, humidity, cloud cover, shade from trees, wind, grass type, grass mowing height, and some other factors. When you put all that together, every 2 weeks seems to work for most everyone. If it does not work for Florida sand, we need to hear about it here. What does work? Daily watering is NOT the answer. I live in the desert and here it is mid July. I'm just now getting around to watering my St Aug. My situation is different for the reasons listed, but in any case, infrequent watering is better than frequent watering. Once you are watering infrequently the weed problems seem to go away. Weed seeds need continual moisture to germinate. When you go a week or two between watering, the weed seeds never germinate. If you are currently watering daily like most in Florida, you will have to wean your grass off that schedule. I've already written a lot, so if you're doing that, write back and we can tell you how to get off the daily.

Mulch mow at your mower's highest setting - ALWAYS. There is never any reason to lower the mower height for St Augustine. If you have a dwarf variety, set it for the middle. Most people don't have the dwarf, so start with it at the highest. My personal preference is to keep my lawn at 12 inches (again, different situation). This is a water conservation project and it's working.

Fertilize with organics. Why? Because you can do it any day of the year with no hassle. With chemical fertilizers there is a long label to read. My alfalfa comes in a plain brown bag with no label. Just apply at 20 pounds per 1,000 square feet - no hassle. In the deeper south you can fertilize on all the big federal holidays. I start on Washington's Birthday, then Memorial Day, 4th of July, Labor Day, and Thanksgiving. If you want to fertilize less often, then use Memorial Day, Labor Day, and Thanksgiving.

If you follow that advice you should have a dense mat of dark green St Augustine. You should not need weed killer, but if you do, then just spot spray. With organic insects do not seem to be a problem. The reason is biological and has to do with the health of the soil microbes as well as the health of the insects when eaten by birds, lizards, geckos, and toads. It's very complicated but healthy soil and healthy insects seem to balance everything.

I'll keep that in mind but it appears i have the Floratam variety and the person at Bayer that I talked to this morning has informed me that the lawn will die, no if ands or buts, it will die. So I have a landscaper coming tomorrow to give me an estimate to replace it.

Lesson learned, unfortunately it will be an expensive one. I'll know the next time. Funny thing is I was planning to let someone else handle the lawn once I got the lawn free of weeds. Uggh, frustrating but I know I'll never make that mistake again. I'll keep all of these tips in mind once I get the new lawn put in. I'll make sure I share them with the lawn guy I will be hiring. :-)