I believe that is coarse bladed zoysia. Not sure if it is too hot to use weed killer end hose sprayer??? First picture looks like crabgrass so look for weedkiller specifically for it. Make sure to do some research of when to apply weed killer at certain temperature.

Try one time application of 15-5-10 then go with organic fertilizer from there on.

Water weekly at 1 inch (600 gallons per 1000 sqft) if needed. Watering everyday will make weed problems worse.

If it is St Augustine, daily water will lead to disease and dead lawn.

1. does look like crabgrass taken through a lens with Vasoline on it.
2. don't know
3. horse herb. This stuff will take over in St Augustine.
4. if the blade tips are blunt, then St Augustine. If they are pointed, then either zoysia or centipede. Centipede only grows under very bad conditions, so to get that dense it would have to be pretty neglected. If it responds well to fertilizer and water, then it is not centipede.
5. dunno
6. sand and thin St Aug - at least it looks like it from that altitude and focus level.

If that is St Augustine or centipede, the herbicide I would suggest is this one.

{{gwi:86656}}

Read the directions carefully. This stuff is not something you want to get on you. You can only apply once a year. If it is too hot now, then wait until it cools off in the fall - read the directions.

If you apply the chemical fert that lou suggested, you could go ahead and apply alfalfa pellets at the same time. App rate for YOU, first app of alfalfa, is 10 pounds per 1,000 square feet. That is because your soil has no nuthin in it. Wait 3 weeks and then you could apply at 20 pounds per 1,000 square feet thereafter. If you want it to improve at record speed, apply the alfalfa monthly for the rest of the season.

Put some cat food or tuna cans out and time how long it takes your sprinkler to fill them. That is your target time for watering. The day you do that test is day 1. Then watch the grass carefully to see how long it goes before ANY part of it looks wilted. Then water a full inch again that day. Watch to see if it goes a day or two longer before wilting. As the grass matures it should go longer and longer between watering.

Mow at your mower's highest setting.

DCHALL,

Here's a picture of my zoysia grass... That looks like OP's grass.

I was thinking the first one looked like chickweed. I see more broad-leafs than blades.
Use metsulfuron products to get the lawn back to new.

Fertilize the existing grass to get it going again.

I am in Central Florida and have large patches of the same grass as picture #1. It is located on a slope which leads to the drainage ditch in the back yard. I did some research and it appears to be centipede grass. It doesn't bother me much because it is between the yard and a conservation area. Is there any reason that I should be concerned about it? Will it take over the St Augustine if it is healthy?

Any advice would be appreciated.

glwoodz, centipede does not bulge in the middle of the blade like that in foto #1. If you actually do have centipede, the easiest way to kill it out is to water weekly, mow high, and fertilize at least 3x per year. That is normal care for normal grass. Centipede cannot stand normal care. It thrives on neglect.

Thanks for the response San Antonio. . I'll try to post a picture to confirm, At one time I thought it was some kind of fungus because it turned brown. The patches are thinner than the St Augustine and the ground looks sunken in,it is also kind of spongy to walk on. We had some heavy rains last week and the areas turned green again.I pulled up some of the grass and did an online search and came up with centipede grass. We have just recently fired our lawn service, they kept saying that it was some kind of aquatic weed. I don't have much faith in their assessment.