A couple years ago on another forum there was a discussion about the use of baking soda to kill crabgrass in St Augustine lawns. Cactus, one of the members of that forum, decided to test the theory. Fortunately for the rest of us, he took lots of pictures and created a movie for YouTube. This video link of cactus' work was recently posted on the organic forum. Sound is low so turn your volume up. Dallisgrass (a perennial) is quite often mistaken for crabgrass (an annual). Here are some pictures. The image above is dallisgrass. The image below is crabgrass. You can see how they would be confused. Here is the most distinguishing feature - the seed head. The image above is the dallisgrass seed head. Note it has three spikes on a stalk. This is a crabgrass seed head. It is a brush type of seed head with anywhere from 2 to 9 spikelets.

Thanks for the replies! To texas-weed: I guess I was mistaken in my thinking that SA would go dormant during drought. I guess those spots are truly dead then. What I did when we moved in was go around the yard and look at the brown grass for any sign of green. In the areas where it was all brown, I raked heavily until it was mainly bare soil and then put down some topsoil with compost. In those areas, the SA is filling in slowly now as long as I keep ahead of the crabgrass. Oddly in the areas with even one or two crabgrass plants, the SA will not grow. I guess those things just suck all the nutrients out or have something that inhibits growth of anything else around it? To fairview: I've pulled ALL the crabgrass I could find in my yard. So anything still there is something small that I've missed, or something that hasn't popped up yet. Part of the problem here is the vacant lot next door that is about 90% covered in very large, mature crabgras. I went and got one of the big concentrate bottles of round up and put it in my sprayer and nuked that lot yesterday. If I can get rid of that stuff, I'm crossing my fingers that as long as I take care of my lawn properly and keep ahead of the crabgrass, I can keep things under control until the SA fills back in. If I have another mass infestation, I think I will pull and then apply Dimension. It is just REALLY frustrating when you pull everything you can see, then the day after you water you go out and theres a dozen new sprouts coming up.

Most of the time, the blue is just tracker dye. It can be added to most herbicides. You can buy it yourself at most Tractor Supply stores, but it's nothing magic--just dye to make sure you don't re-spray an area a second time. As to what the actual chemical is, that could be almost anything...

Several years ago there was some experimenting going on with the use of baking soda as a solution to crabgrass in St Augustine. It was quite a big discussion on another lawn forum. Here's the video the guy made. CAUTION: THIS ONLY WORKS WITH SALT TOLERANT GRASSES LIKE ST AUGUSTINE. It does not work with bermuda. The trick is to get the baking soda to stick to the crabgrass blades. You do that by wetting the blades with water. The trick to that is crabgrass blades are hydrophobic and will shed water. The trick to that is to moisten the crabgrass blades with soapy water or with a touch of molasses in it. So you moisten the blades with soapy water, dust the baking soda on (watch the video), and sit back. The crabgrass will turn black quickly and die. The St Aug might suffer a little but it comes right back. The St Augustine might fill in during the summer heat but it fills much faster when temps are in the 70s.