There are several species of grass in the genus Cenchrus that bear the name "sandbur," but the two most common in Maryland are native species. Accounts vary about their life cycle; most references say they are annual, but some say they can occasionally behave like a biennial (lives for two years) or a perennial.

We don't have a reference list of which pre-emergent chemicals target which specific weeds, but if you look for a product labeled to kill grassy weeds in a lawn, that may work (though see if it includes sandbur on its list of weeds controlled). Authorities like Cornell mention that sandbur does not compete well with crops, which in this case should also include an established lawn, assuming the lawn is healthy and vigorous. Given the sandbur takeover, it may not be, either due to stress from repeated soil compaction from foot traffic, root stress during drought or flooding events, or other factors. Perhaps the weeds found it easy to take over an area of lawn if the turfgrass was already sparse or struggling to thrive due to inadequate sun or less-than-ideal soil conditions.

Examples of ingredients that control grasses (and in some instances, potentially also some broadleaf plants, in case you deliberately have some clover mixed into the lawn) as a pre-emergent include Prodiamine, Dithiopyr, and Pendimethalin. There may be other options, however, and always read the product label directions thoroughly to determine if the product is suitable for your situation (allowed for residential lawn use or road rights-of-way as opposed to pastures or other sites; able to be used in areas with a high water table or near open water; etc.).

In case you were considering doing so, be aware that the use of nearly any pre-emergent for grassy weed control will mean that you will not be able to overseed the lawn this spring, if your lawn is made up of cool-season fescue grasses. (Overseeding those types of lawns is best done in early autumn anyway.) If the lawn is zoysia instead, that conflict isn't a concern, since zoysia is not overseeded. Which turf type is growing there -- fescue or zoysia -- will also determine if any given herbicide is at risk of damaging the grass, since some products may target warm-season grassy weeds (zoysia being warm-season also) since they are a common group of grassy weeds that grow in cool-season lawns.

When to apply a pre-emergent depends on the weather and the chemical involved, so see what the label says for a product you choose. If similar in growth cycle to crabgrass, then an annual sandbur may germinate around the time the soil temperature (about two inches down) reaches about 55 degrees for a few consecutive days. In your area, that might be occurring about now (at the end of March).

To complicate matters, at least one reference says that sandbur may behave as a winter annual, meaning that it would have germinated back in autumn, overwintered, and will finish its life cycle this spring and die off. (In comparison, crabgrass is a summer annual, which germinates in spring and dies by autumn.) If you don't see any small, young sandbur plants already in the lawn, then the plant is probably growing as a summer annual and hasn't germinated yet. Some pre-emergent products are applied twice, once prior to germination (perhaps a couple weeks prior, but it may vary) and once a few weeks after, to catch late-sprouting seeds.

Depending on how infested the lawn became, it might take more than one season to get the sandbur eradicated, and depending on the chemical used and how stressed the lawn may be at the time of application, some temporary discoloration to the turfgrass might result from herbicide use, though it should recover on its own in that case.

We don't know what specific herbicides may be restricted so close to the water, such as in a Critical Area or Critical Area Buffer, you would need to check with local government, or the county Extension office may know.

Miri