Sandspurs are a Summer Annual that will appear in your grass in the springtime after it as been killed off in the winter.
Sandspurs need to be treated early in the year with a Pre-Emergent such as Dimension (Weed and Grass Stopper)
See our lawn calendar guide:
These weeds will throw hundreds of seeds so preventing them to begin with is the best way.
If you already have sandspurs you should start with Weed and Grass stopper to prevent any seeds from germinating further and then treat the problem with a post-emergent such as Sedge Ender– which is also good for sedge treatment.