I see about 1 blade of St Augustine in there, so yes, you can reclaim this lawn to a full SA showplace. St Aug spreads about 5 feet in all directions every spring and again in the fall. It will take at least a full season of care, but I've done it many times.

Do this

1. Reset your mower to the highest position and weld it there. Never change it. St Aug loves to be tall - the taller the better. In fact skip a week between mowings.

2. Water once a week but water deeply. Continue the weekly watering even as the temps cool down. This extra water will help the St Aug spread. If you can, water only the St Augustine. Grass should be watered about 1 inch of water per week, all at one time. If you spread out the watering to daily, for example, the soil will be continually moist and every weed seed in there will sprout. You don't want that. Let the soil surface dry completely between watering to stop the birth of new weeds. If your grass continues to grow into the winter, then continue with watering every 2 weeks. Once the lawn is reestablished as SA, you can go to once per month watering in the cooler months with temps below 70.

3. Sprinkle a handful of alfalfa pellets (rabbit chow) on each clump of St Aug but none on any of the bermuda, crabgrass, or other invaders. You can do this every month or even every week if you want to. Alfalfa is a great organic fertilizer. As the St Aug spreads you will need to follow along the runners with the alfalfa. Bermuda practically requires heavy monthly feeding. When you deny the bermuda its food, it will thin leaving more soil and sunlight for the St Aug to spread make inroads where the bermuda once was.

4. If you have larger areas with more St Aug already, and you are convinced there is no disease in the grass, then you can spray something like the Spectracide black bottle with the purple label herbicide. That's the one with atrazine. Use it only once per season. It will take out most weeds and severely thin out the bermuda within a few weeks. The St Aug will only be slightly damaged if at all. Herbicides are always foliar mist products and not soil drench, so use it judiciously.

As an experiment I have a yard full of unmowed St Augustine, so when I say it loves to be tall, I know what I'm talking about. I have not mowed it since Oct 2011. It will grow up to 32 inches high and then stop growing. I think it becomes too dense and shades itself out at that point. The point of my experiment was to see how long I could go without watering it. Once it gets up taller than 20 inches it doesn't seem to need any water. Shorter than that and it needs water only when the humidity drops below 40%. You should not have any problem with that, but then, you're not doing the experiment. My point is tall St Augustine will really take over with minimal care. For your purposes, definitely go 2 weeks between mowing. It will grow up to about 6-9 inches and you will be mowing it back to 4. No problems. I know the mantra is to mow no more than 1/3 off but this will work. Once you have it close to perfect, then you can go to weekly mowing.

Please post another picture showing the St Augustine with the camera about 3 inches away from the blades. I'm looking for signs of fungal disease. I see discoloration in this one picture but I can't tell what it is. Also, sharpen your mower blade.

Here is one picture

And Another

I have also noticed that when I let it grow longer, i get a lot mushrooms growing in my front yard. Any suggestions?

The lesions on your St Augustine are from a fungal disease. It will erase the last of your St Aug if you don't stop it. They are caused by too much moisture and not enough air movement. It could be the grass was covered up with other garden clippings for a day. That's all it takes.

Mushrooms are not a problem - they are a symptom. They are not a symptom of taller grass, but they are a symptom of too much moisture on the soil. The lesions together with the mushrooms are telling me you are too wet. Are you getting a lot of rain this year or are you watering more than once per week?

Since 2002 I have had excellent results from applying ordinary corn meal to get rid of that same fungus you have. I apply it at 20 pounds per 1,000 square feet over the entire yard to get it all. And if you don't do the entire yard, the part you applied to will turn dark green and the rest will not. Corn meal is an organic fertilizer. Apply the corn meal and wait 3 weeks for signs of improvement. If it does not work, then you will have to wait until the temperature conditions are cool enough to apply a chemical fungicide. That can be weeks.

You can usually find ordinary whole ground corn meal at a feed store in plain brown 50-pound bags for around $20. When I first started with corn meal in 2002 it was $3 per bag. For control of fungal disease you do not want to use the corn gluten meal product. Those are two different products from the same plant, but they seem to work differently.