Dallisgrass (Paspalum dilatatum) is an aggressive, warm-season perennial grass that poses a significant challenge to turf management, particularly in southern and transition zone climates. Unlike annual weeds, this perennial returns season after season, making it exceptionally persistent. Its difficulty to control stems from its deep, fibrous root system and thick rhizomes, which allow it to survive harsh conditions and quickly regrow. It also produces a large volume of seeds rapidly throughout the growing season, ensuring widespread infestation. Managing this weed requires a systematic approach combining accurate identification, targeted killing of established clumps, and long-term prevention strategies.
Identifying Dallisgrass
Accurate identification is the first step in effective removal. Dallisgrass grows in coarse, grayish-green clumps that stand noticeably taller than surrounding turfgrass, giving the lawn a patchy texture. The leaf blades are wider than most turf varieties, typically measuring between one-quarter and one-half inch across. A distinctive feature is the presence of long, silky hairs located near the leaf collar.
The most recognizable sign of infestation is the production of a unique seedhead, which rises on a tall, thin stalk above the lawn canopy. This seedhead consists of three to five finger-like spikes emerging from a central point. The seeds (spikelets) are arranged in four rows along these spikes, often exhibiting a dark brown or black coloration at maturity. The plant spreads by these seeds and through short, thick rhizomes, allowing the clump to expand.
Non-Chemical Removal Techniques
For small or isolated clumps, physical removal avoids the use of herbicides. Simply hand-pulling is ineffective because the plant’s robust root system and rhizomes remain in the soil, leading to rapid regrowth. Successful non-chemical removal requires “shovel work,” where the entire plant, including the root crown and all associated rhizomes, is dug out of the turf. This process is easiest when the soil is moist, allowing for the complete extraction of the dense root mass.
After digging out the clump, the resulting bare spot must be immediately filled with topsoil and reseeded or sodded with desirable turfgrass. Leaving the area bare allows new Dallisgrass seeds to germinate and establish. For larger, dense patches, smothering the area is an effective non-chemical option. Covering the infestation with a thick layer of black plastic or landscape fabric during the summer months will solarize the area, killing established plants and reducing the viability of buried seeds.
Targeted Chemical Control of Established Plants
For widespread or heavily established Dallisgrass, selective post-emergent herbicides are necessary to achieve control without destroying the entire lawn. Effective active ingredients target the weed while sparing the surrounding turf, such as quinclorac, mesotrione, or professional-grade products like MSMA or Celsius WG. These systemic herbicides are absorbed by the leaves and translocated down to the rhizomes and roots, disrupting the plant’s growth processes.
Timing the application is a major factor in achieving success. Dallisgrass is most susceptible when actively growing and translocating energy to its roots, which occurs in the spring and early summer, and again in the late summer or early fall. Treating the plant during the late-season period allows the herbicide to be pulled down into the perennial root system as the plant prepares for dormancy, leading to better long-term eradication. Multiple applications, typically spaced two to four weeks apart, are required to achieve adequate control of established clumps.
Applying the product as a spot treatment, directly targeting the clumps, minimizes exposure to the surrounding lawn. Including a non-ionic surfactant in the spray mixture is beneficial, as it improves the herbicide’s adhesion and penetration into the Dallisgrass’s coarse leaf structure. In areas where the weed has completely overtaken the turf or in non-lawn areas, a non-selective herbicide containing glyphosate can be used to kill all vegetation. This approach creates a large bare patch that must be promptly reseeded to prevent future weed invasion.
Preventing Future Growth
Preventing Dallisgrass from returning is a multi-year effort focused on stopping new seedlings and improving turf health. The primary tool for prevention is the use of pre-emergent herbicides, which create a chemical barrier in the soil that inhibits seed germination. Active ingredients like dithiopyr or prodiamine are effective against Dallisgrass seedlings.
Timing the pre-emergent application is critical, as it must be done before the seeds begin to germinate in the spring. Germination typically occurs when soil temperatures reach a consistent range of 60 to 65 degrees Fahrenheit. Because Dallisgrass is a perennial that can germinate over a longer period, applying a split application—two treatments spaced weeks apart—provides a longer protective window.
Long-term control relies heavily on cultural practices that favor the desired turfgrass over the weed. Maintaining a dense, healthy lawn naturally suppresses Dallisgrass seedlings by crowding them out and limiting light penetration. This includes mowing at the highest recommended height, which promotes deeper rooting and thicker growth. Proper fertilization and aeration also contribute to a robust turf canopy that resists establishment.