The weed these people are asking about is called spurweed or lawn burweed. Many folks mistakenly call it sandspurs, which technically is called sandbur and is a different summer weed.
Spurweed is a winter annual weed that grows very close to the ground. As temperatures warm in the spring, spurweed grows rapidly and begins to form spine-tipped burs in the leaf axis that hurt when you walk on them barefoot.
Part of the problem with control is that a couple of our most common pre-emergence herbicides that many people use in the fall – Dimension, Balan, and Crabgrass Preventer – are poor in preventing spurweed. The only two that do a pretty good job are pendimethalin (also sold as Halts) and atrazine. Atrazine can be bought as a liquid or granular herbicide and it also comes in a Weed-N-Feed such as Bonus S. In the fall months we should only be using the herbicide and not the fertilizer. But atrazine only lasts about a month in the soil as a pre-emergent. Pendimethalin will typically last three to four months during the cooler months of the year.
Spurweed can be easily controlled during the winter months using post-emergent herbicides such as atrazine, imazaquin (Image) or the three-way mixtures of 2, 4-D, MCPP, and dicamba (Weed-B-Gon, Weedstop, Weed Killer for Southern Lawns, etc.).
For someone with a Bermuda or zoysia lawn, Image would be my first choice as it works better than the 2,4-D mixtures and is safer on the grass. For St. Augustine and centipede lawns I would use Image or atrazine.
December, January and February are ideal months to apply post-emergent herbicides. The problem, though, is most people just don’t notice the weeds or take action until it is too late. Once the weed has changed from the vegetative, or growth stage to the reproductive, or flowering stage it becomes very difficult to kill with a weed killer. So then it takes multiple applications and you risk injuring the grass. Plus, once the spiny burs have come on the plant, it doesn’t matter if the weed plant is dead or not, the burs persist until they naturally decompose.
If you only have a few of these plants in your lawn, the best thing to do is to manually dig them up. This will certainly help in getting rid of potential plants for next fall. This may not be practical in a big lawn with a lot of weeds. Spurweed usually persists in the lawn through May, depending on how early it gets hot and stays hot. In cooler springs, it may hang on until sometime in June.
Going back to the herbicides I mentioned, the only one that would be worthwhile in using this late in the spring are the 2,4-D mixtures, using the full rate on either Bermuda or zoysia since they work fairly quickly as oppose to Image and atrazine which work very slowly. On St. Augustine or centipede, you must cut the rate in half so it would not give you good control, meaning a second application would be needed. You might as well let the heat kill them if you can’t manually pull them up.
If this weed has given you problems for several years now, remember these control measures so you can take action earlier in the season. It takes a good combination of pre and post emergence herbicides, combined with some good old fashion hand pulling, to fully lick this weed problem in one season.