Dallisgrass (Paspalum dilatatum) is a persistent, warm-season perennial weed that presents a significant challenge to homeowners seeking a uniform lawn. This invasive grass forms unsightly, coarse clumps and quickly colonizes turfgrass areas, making it difficult to eradicate. Its ability to thrive in hot, humid conditions means that control requires a diligent, multi-faceted strategy to identify, manage, and ultimately remove this weed.
Identifying Dallisgrass and Its Growth Habits
Dallisgrass is easily recognized by its distinct growth pattern, forming dense, circular tufts that stand out from desirable turfgrass. The leaves are generally a lighter, coarser green than most lawn varieties, featuring broad, flat blades with a prominent midrib. At the base of the plant, the leaf sheaths often exhibit a purplish or reddish tinge, which aids in identification.
The most defining characteristic is the seed head, which emerges on a tall, slender stalk, often escaping the mower blade. These seed heads are branched in a raceme structure, with three to seven spikelets that resemble tiny fingers. Its perennial nature makes it difficult to control; it possesses short, thick rhizomes and a deep, tenacious fibrous root system that stores carbohydrates. This robust underground structure allows the plant to survive harsh conditions and regrow even after the top growth has been cut.
Manual and Cultural Control Strategies
For small or isolated clumps, physical removal is the most direct non-chemical method. Successful manual control necessitates digging out the entire plant, including the extensive root mass and any short rhizomes. The crown and root system must be removed completely, typically requiring the removal of soil several inches deep and wide around the clump.
Leaving behind even a small fragment of the crown or root can lead to immediate regrowth, meaning this method is labor-intensive and best suited for minimal infestations. Once the clump is removed, the resulting hole should be filled with fresh topsoil and immediately reseeded or sodded to prevent new weed establishment.
Cultural practices are equally important for long-term suppression by maximizing the health and density of your turfgrass. Mowing the lawn at the highest recommended height encourages a dense canopy that shades the soil, inhibiting Dallisgrass seed germination. Deep, infrequent watering is recommended, as this practice favors the established turfgrass over Dallisgrass, which often thrives in overly moist areas. Promoting a vigorous lawn through proper fertilization and overseeding bare patches creates competition that naturally crowds out the weed.
Targeted Chemical Treatment Options
Chemical control of Dallisgrass involves two distinct approaches: prevention using pre-emergent herbicides and treatment of established plants using post-emergent herbicides. Pre-emergent herbicides form a chemical barrier in the soil that prevents seeds from germinating. For effective control, these must be applied in the early spring, before Dallisgrass seeds begin to sprout, typically when soil temperatures consistently reach 60 to 65 degrees Fahrenheit.
Common active ingredients for pre-emergent prevention include dithiopyr or prodiamine. These must be applied at the correct timing to disrupt the weed’s life cycle. While pre-emergents are effective against new seedlings, they will not control existing perennial Dallisgrass plants.
Treating established clumps requires a selective post-emergent herbicide that targets the weed without harming the surrounding turfgrass. Dallisgrass is notoriously tolerant of many standard lawn herbicides, making selective control challenging. Specific selective active ingredients that have shown efficacy include quinclorac or specialized sulfonylurea herbicides such as Certainty or Monument.
Professional-grade products containing MSMA (monosodium methyl arsenate) or DSMA (disodium methyl arsonate) are also highly effective, though their use is often restricted to licensed professionals or specific sites like golf courses. Due to the plant’s robust root system, established Dallisgrass often requires multiple sequential applications—typically two to three treatments spaced several weeks apart—for complete eradication.
For heavy infestations or individual, stubborn clumps, a non-selective herbicide like glyphosate can be used as a targeted spot treatment. This approach will kill any vegetation it contacts, including the desirable turfgrass, so careful application is necessary to minimize damage to the surrounding lawn. Fall is often the most effective time for post-emergent applications, as the plant is actively moving resources to its roots, allowing the systemic herbicide to be transported throughout the entire plant for a more complete kill.