Dallisgrass (Paspalum dilatatum) is a persistent, perennial grassy weed that challenges turfgrass across the United States. This weed is difficult to eliminate because it grows rapidly, produces abundant seedheads, and establishes a robust root system with short, thick rhizomes. Successfully removing this coarse grass without damaging the surrounding lawn requires a highly selective treatment strategy. Because dallisgrass is perennial, it returns year after year from its underground structures, often necessitating a multi-season approach for effective control.
Identifying Dallisgrass from Desirable Turf
The first step in selective removal is accurately confirming the presence of dallisgrass, which is often mistaken for other common grassy weeds like crabgrass. Dallisgrass is easily identified by its coarse texture and its habit of growing in unattractive, noticeable circular clumps or tufts that stand taller than the surrounding turf. The individual leaf blades are typically wider than those of fine turf grasses, appearing a distinct grayish-green color, and they often possess a prominent midrib down the center.
A defining characteristic that differentiates it from annual weeds is the presence of short, thick underground stems, called rhizomes, which allow the plant to spread and survive year-to-year. The plant also produces distinct, whip-like seed heads on tall stalks that rise significantly above the mowing height of the lawn, usually from late spring through fall. These seed heads feature three to seven spikelets arranged along a central axis, often showing small black spots on the seeds. In contrast, desired turf like Bermuda grass spreads via above-ground stolons or Fescue grass grows as individual shoots without the prominent clumping habit or thick rhizomes of dallisgrass.
Selective Chemical Strategies for Elimination
Because dallisgrass is a perennial grass growing within a lawn of desirable grasses, control relies on selective post-emergent herbicides that target the weed while sparing the turf. Successful eradication requires multiple treatments. The most effective window for treatment is when the weed is actively growing, typically in late spring or early summer, and again in the late summer or early fall. Targeting the plant during these periods allows the herbicide to be absorbed and translocated down to the rhizomes before the weed enters winter dormancy.
For warm-season grasses like Bermuda and Zoysia, one of the most historically effective active ingredients was Monosodium Methylarsonate (MSMA). However, MSMA is now severely restricted by the EPA and is generally not available for residential lawn use, being largely limited to commercial sites like golf courses and sod farms. This restriction has led to the increased reliance on alternative selective herbicides. For warm-season turf, products containing Sulfosulfuron (such as Certainty) or Foramsulfuron (such as Revolver) provide selective post-emergent control or suppression of dallisgrass.
Quinclorac is a common alternative herbicide used for selective control in many turf types, including some warm-season and cool-season grasses. While Quinclorac is highly effective against young dallisgrass seedlings and other grassy weeds like crabgrass, it may provide only limited control of mature, established clumps compared to other options. For cool-season turfgrasses, specifically tall fescue, the active ingredient Fluazifop (found in products like Fusilade II) is often the recommended selective post-emergent option. This product can selectively remove grassy weeds from broadleaf plants and certain cool-season grasses, offering a viable solution for dallisgrass control in fescue lawns.
Reading the product label is paramount, as herbicide compatibility depends entirely on the specific turfgrass species in the lawn. For instance, Mesotrione is another selective option for some warm-season grasses but is not safe for use on Zoysiagrass or Bermudagrass. The label will specify the correct application rate, the number of sequential applications required, and any temperature or timing restrictions to ensure maximum weed kill while preserving the desirable grass. Complete eradication often requires two to three sequential applications spaced several weeks apart.
Cultural and Mechanical Control Methods
For small, isolated infestations, mechanical removal is a highly effective, non-chemical control method. This process involves physically digging out the individual clumps, ensuring the removal of the entire plant, including the short rhizomes and all roots. Any fragments of the rhizome left in the soil can potentially regrow, leading to the weed’s recurrence. This method is best performed when the soil is moist, which helps ensure the entire root structure can be lifted cleanly from the ground.
Long-term management relies on cultural practices that favor the desired turfgrass over the weed. Dallisgrass thrives in thin, stressed lawns, so maintaining a dense, vigorous stand of grass is a primary defense against weed establishment. Adjusting the mowing height is a simple yet effective strategy, as keeping the desirable grass slightly taller shades the soil surface. This shade suppresses the germination and establishment of new dallisgrass seedlings.
Proper irrigation techniques also aid in prevention, as dallisgrass is often found in heavily or frequently irrigated areas. Shifting to deep and infrequent watering encourages the desirable turf to develop deep roots, making it more resilient, while creating a less favorable environment for weed seeds to germinate. Finally, consistent fertilization practices should be implemented to promote the health and density of the preferred turf species. A healthy, thick lawn naturally outcompetes dallisgrass and minimizes the open soil areas where its seeds can successfully sprout.