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Old 06-24-2012, 06:13 PM
greendoctor greendoctor is offline
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Join Date: Mar 2008
Location: Honolulu, Hawaii
Posts: 8,181
Originally Posted by RoboMike View Post
Hi All,

We bought a house in south florida and the lawn is completely taken over by weeds. I've used a selective herbicide ortho weed b gone and it works on the less problematic weeds like dollar weeds. For the more problematic viney broadleaf weeds that form a dense carpet / mat close to the soil the grass doesn't even have a chance and I really hate those lite purple / pink flowers. Other weeds are like trees with long tap roots. So for those I am using Roundup since it only kills the plants it touches on the leaves and does not leave much residue in the soil.

The problem is that my entire back yard has a weed problem.

We have St. Augustine grass.

So I would like you opinion as I'm not sure if my approach is the best way.

My approach:

Systematically use weed killer on the weeds where I can find them, as often as I can. Then when most of the dense populations of weeds are killed (perhaps most of my lawn) then fertilize the grass every 6 weeks or so in attempts to get the grass to grow and crowd out other weeds.

If I was living back up north, I'd buy seed and over seed.

Which is why I have another question... since you can't get St. Augustine grass in seed, should I combine it with another grass type that I can get in seed? I was thinking Caterpillar grass which is similar to St. Augustine...

Re-sodding, plugs, etc.. is too expensive.

I'd love your help!
The first thing to do with a bad st augustine or any other lawn is check the irrigation. If it does not have one it needs it. If it does, the heads need to be set for uniformity of coverage and correct run time for the soil conditions. Next, you do fertilize, however not with Scotts or any of those miracles in the bag that are nothing more than slow release urea. Fertilization will not benefit the weeds more than the grass. If anything it will help the lawn tolerate herbicide treatment better and set the conditions for the grass to take over while the weeds are dying.

My experience with Weed-B-Gon for Southern Lawns is that it does nothing to the weeds that form mats and have deep taproots. At least not at the dosages safe on st augustine. I have seen homeowners who have a craniorectal inversion thinking that it does work on those weeds because the idea of hiring a CPO hurts their ego. It works when spot sprayed at a gross overdosage that kills the lawn or is applied contrary to the label.

I do know of selective herbicides for broadleaves in st augustine. However, I rather see them applied through calibrated sprayers capable of applying a set dosage to the entire area.
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