Dallisgrass (Paspalum dilatatum) is an aggressive, perennial grassy weed that challenges warm-season turfgrass, particularly established Bermudagrass. This invasive species thrives in hot, moist conditions, forming unsightly clumps that disrupt the uniform appearance of a healthy lawn. Because of its deep root structure and prolific seed production, standard weed control methods are often ineffective. Complete eradication requires a persistent, multi-faceted strategy combining precise identification, targeted chemical application, and proactive cultural practices.
Identifying Dallisgrass and Manual Removal
Correct identification is the necessary first step, as dallisgrass is often mistaken for common annual weeds like crabgrass. Dallisgrass grows in dense, circular clumps with coarse, grayish-green leaf blades that are notably wider than typical Bermudagrass. The blades often have a prominent midrib and a slightly hairy texture near the base where the leaf meets the stem.
Its most distinguishing feature is the seed head, which emerges on a tall stalk, displaying three to six spikes arranged like waving fingers. These spikes are lined with flat, oval seeds that are easily spread by mowing or wind, allowing the weed to propagate rapidly. Unlike annual weeds, this perennial species survives winter due to its short, thick underground stems, known as rhizomes.
Manual removal is a viable option for small, newly established infestations, but it demands thoroughness due to the plant’s perennial nature. The entire clump, including the deep crown and all associated rhizomes, must be completely dug out to prevent regrowth. This is best accomplished when the soil is moist, allowing for easier extraction of the entire root system. If a small fragment remains, the plant will likely regenerate, making chemical control a more realistic strategy for widespread presence.
Targeted Chemical Control Options
Eradicating established dallisgrass requires selective post-emergent herbicides designed to target the weed without harming the Bermudagrass turf. Since dallisgrass is a grassy weed, common broadleaf weed killers are ineffective, necessitating the use of specialized active ingredients. These systemic herbicides are absorbed by the plant’s foliage and transported to the roots, providing a more complete kill.
One of the most effective options for professional use is a class of sulfonylurea herbicides, such as those containing trifloxysulfuron-sodium (Monument) or a combination of foramsulfuron and thiencarbazone-methyl (Tribute Total). These compounds are labeled for selective control in established Bermudagrass and are more potent than consumer-grade products. Multiple sequential applications, typically spaced several weeks apart, are necessary to achieve high levels of control due to the weed’s robust root system.
Monosodium Methanearsonate (MSMA) is now heavily restricted and generally unavailable for residential lawn use due to environmental regulations concerning its arsenic content. Homeowners should avoid products containing quinclorac, as this is primarily effective for crabgrass and only provides inconsistent suppression of mature dallisgrass. For isolated clumps, a non-selective herbicide like glyphosate can be used as a targeted spot treatment, though this will kill the surrounding Bermudagrass and leave a temporary bare spot.
Complementing the post-emergent strategy is the application of pre-emergent herbicides like prodiamine or dithiopyr, which prevent new dallisgrass seeds from germinating. While pre-emergents will not kill existing plants, they are an indispensable component of long-term management. These products should be applied in early spring when soil temperatures reach 60 to 65 degrees Fahrenheit, before the seeds begin to sprout. Consistent use of pre-emergents significantly reduces overall weed pressure and the reliance on intensive post-emergent treatments.
Optimal Timing and Application Techniques
The timing of post-emergent herbicide application is directly linked to its effectiveness, as the dallisgrass must be actively growing to absorb and translocate the chemical to its roots. The most susceptible periods for treatment are during active growth, typically from late spring through early fall, when air temperatures are consistently above 60 degrees Fahrenheit. Late summer and early fall applications, before the weed enters dormancy, are particularly effective because the plant actively moves carbohydrates to the root system, drawing the herbicide with it.
It is necessary to follow label instructions regarding temperature limitations, as applying herbicides when temperatures exceed 90 degrees Fahrenheit can cause significant injury to the surrounding Bermudagrass. Most systemic products require a follow-up application after 10 to 14 days or up to six weeks, depending on the active ingredient, to ensure a complete kill. This sequential treatment strategy targets surviving plant tissue and newly emerging growth, maximizing the chances of full eradication.
Proper application technique is paramount for success and minimizing damage to the turf. Spot treatment, rather than broadcast spraying, is often recommended for selective herbicides to limit chemical exposure only to the weed clumps. Many professional-grade herbicides require the addition of a non-ionic surfactant or methylated seed oil (MSO) to the spray mixture. This additive helps the herbicide penetrate the weed’s waxy leaf surface, ensuring better absorption and translocation.
When using a non-selective product like glyphosate on dormant Bermudagrass, the application must be precise, targeting only the green dallisgrass clumps. It is important to wear appropriate personal protective equipment (PPE), such as gloves and eye protection, and to avoid spraying on windy days to prevent drift. Watering should be withheld for 24 to 48 hours after application to allow the herbicide to be fully absorbed.
Long-Term Prevention and Lawn Rehabilitation
After killing dallisgrass clumps, the focus shifts to preventing recurrence and encouraging the Bermudagrass to spread into the bare spots. The foundation of long-term weed prevention is maintaining a dense, healthy Bermudagrass turf that can naturally outcompete invasive species. This is achieved through proper cultural practices that favor the turfgrass over the weed.
Bermudagrass should be mowed at a consistent, low height, typically between one and two inches. Mowing should be frequent enough to remove no more than one-third of the blade height at a time, which encourages lateral growth and density. Deep, infrequent watering is preferred, as it encourages the Bermudagrass to develop deeper roots while discouraging the shallow-rooted dallisgrass.
Soil health is another factor, and a soil test can determine if proper fertilization is needed to support vigorous Bermudagrass growth. Applying adequate nitrogen during the peak growing season will fuel the turf’s spreading habit, accelerating the repair of bare patches. In areas where large clumps were removed, lightly topdressing with a sand-soil mixture can help smooth the surface and provide a better substrate for the Bermudagrass stolons to spread.
For faster recovery, the bare areas can be manually plugged or seeded with Bermudagrass, although the existing turf usually fills in naturally over a single growing season. The combination of pre-emergent application and a robust, dense turf canopy provides the best defense against future dallisgrass invasion. Controlling this weed is a sustained effort that integrates chemical treatments with vigilant maintenance practices.