I'm posting this in several places because it is important..

San Antonio is having our annual fall blooming of the Texas rainlily plants (cooperia pedunculata). If you have them and don't want them, you must collect the seed pods BY HAND before they ripen and break open. The first time you see one in your yard, it seems pretty innocuous; however, each plant creates about 30 new seeds that seem to explode in the general area of the first plant. When it rains again each new plant will create 30 more. Here's how that goes.
Second season - 30 plants
Third season - 900 plants
Fourth season - 27,000 plants
Fifth season - 810,000 plants

Unless you want to have a lawn of wildflowers, you really need to mow these things down before they can seed. I try to get them in the flower stage.

These plants have a peculiarly toxic reaction in cattle. They cause sunburn and stop milk/meat production. If you have them in a pasture, you really want to get rid of them before letting the livestock in.



Texas Rainlily (Cooperia pedunculata)

I have a few of these and I like them a lot. Granted, I do not have cows. I wish they would spread, but I guess the thick St. Augustine is prohibiting this...
That being said, it may be that other grasses, when thick enough, will prohibit these from becoming a nuisance. I noticed in the picture you posted that the vegetation seems sparse. Maybe an application of well-suited seed would help!