Mat Sandbur, more commonly known as grassburs - or "stickers", are a common problem in the Texas Hill Country. A natural solution for grassburs is corn gluten, a natural non-selective, pre-emergent herbicide. You must have it in place and active before the grassbur seeds sprout. Once the plants are growing, there isnt' much you can do beyond hoeing, Round-up, or an IED (improvised explosive device like they use in Iraq). Since hoeing is too much work, people reading my blog are not likely to use Round-Up, and IEDs usually cause some collateral damage (such as burning your house down or killing the cat), I suggest using corn gluten now.
For our area, corn gluten should be applied around March 1st. This gives it plenty of time to become active in the soil and still give it coverage through the spring growing season. One application lasts around 10 to 12 weeks. If we have a wet summer or early fall, a second application will be necessary.
Application rate is 10 lbs. per 1000 sq. ft. so a 40 lb. bag covers 4000 sq. ft. Be sure to get horticultural corn gluten - the feed grade stuff does not have enough active ingredient in it. Check the tag and make sure that nitrogen is at least 9 percent. (A nice "side effect" of corn gluten is the greening power derived from the high nitrogen content!) Also, if you have a choice, get the granular version. Some people sell a powdered version which works well and is a few dollars cheaper but it will paint your legs yellow from the knees down and the wind will scatter most of it on your neighbors property!
Past customers tell me that you should expect a significant and noticable decline in grassburs in the first year but it takes 3 years to eliminate them.
One caveat, corn gluten is a non-selective pre-emergent which means that is prevents all seeds from sprouting including wildflowers and garden seeds. Don't use where you want other seeds to sprout!