Sand spurs are summer annual weeds that germinate and mature each season. The fruits are felt in the fall, when it is too late to kill the plant using chemicals. Herbicides are not effective on sand spurs once they have bloomed in the fall. Apply a pre-emergent herbicide containing imazapic to the lawn in the spring, following the label directions, according to the University of Florida. Maintaining a healthy lawn will prevent sand spurs from forming.