Dallisgrass (Paspalum dilatatum) is a persistent, warm-season perennial weed that presents a challenge to lawn health across the southern and transition zones of the United States. It is notorious for its aggressive, clumping growth habit, making it one of the most difficult turf invaders to eliminate. Controlling this weed requires a multi-season, systematic approach that combines manual effort with targeted chemical treatments. This guide details the specific methods and products needed to effectively eradicate dallisgrass.
Identifying Dallisgrass and Why It Resists Control
Dallisgrass is identified by its distinctive physical features and growth pattern. It grows in coarse, circular clumps, with leaf blades that are often wider (up to half an inch) and a lighter gray-green color than the surrounding lawn. When left unmowed, the plant produces tall, slender seed heads that rise above the canopy, featuring three to seven finger-like spikes (racemes). Its resilience lies in its biology as a perennial plant with a short, thick, fibrous root system of rhizomes. These underground stems store carbohydrates, allowing the plant to regrow even after the top growth is damaged, and prolific seed production ensures new plants constantly emerge.
Non-Chemical and Manual Removal Strategies
For small, isolated clumps, physical removal remains the most direct and effective non-chemical solution. The entire plant, including the robust root crown and all attached rhizomes, must be meticulously dug out to prevent regrowth. Simply pulling the visible leaves will leave the perennial root structure intact, allowing the weed to quickly return. This labor-intensive process is best suited for spot treatments where the infestation is minimal, requiring a garden trowel or shovel to excavate a wide and deep area. Another option for spot treatment involves using a non-selective herbicide, such as glyphosate, applied directly to the weed, though this will kill all vegetation it contacts and require reseeding afterward.
Selecting the Right Post-Emergent Herbicides
Successfully killing existing dallisgrass patches requires the use of specialized, systemic post-emergent herbicides. These are absorbed by the leaves and transported down to the root system. Selective herbicides are necessary to control the grassy weed without harming the surrounding turf, but their effectiveness depends heavily on the type of grass in the lawn.
Active Ingredients
Active ingredients commonly used include quinclorac, metsulfuron-methyl, and MSMA (restricted for residential use). Quinclorac is often a preferred option for control in specific warm-season grasses and cool-season turf, while metsulfuron-methyl is highly effective in bermudagrass and zoysiagrass. For cool-season lawns, such as tall fescue, products containing fluazifop may provide selective control, though repeat applications are necessary.
Application Timing
The most effective application timing is when the dallisgrass is actively growing, typically in late spring through early summer, and again in the early fall. Multiple sequential applications, usually two or three spaced four to six weeks apart, are required to fully exhaust the weed’s stored energy reserves. Applying the herbicide with a non-ionic surfactant is important, as this additive helps the chemical penetrate the waxy leaf surface, improving its translocation to the rhizomes. Applications made when the average 24-hour air temperature falls below 72°F in the fall tend to be more effective than summer treatments.
Long-Term Prevention and Lawn Health
Long-term control depends on preventing new germination while simultaneously eliminating existing plants. Pre-emergent herbicides are an integral part of this strategy, acting as a chemical barrier in the soil to stop new seeds from sprouting. These products should be applied in late winter or early spring before soil temperatures consistently reach 60°F to 65°F, which is when dallisgrass seeds begin to germinate.
Pre-emergents are effective against new seedlings, but they have no effect on the established perennial plants that overwinter using their rhizomes. Improving the health and density of the desirable turfgrass is equally important in prevention.
Proper cultural practices, such as mowing at the highest recommended height for the turf type, promote a thick canopy that shades the soil surface. This shading reduces soil temperatures and light availability, creating an unfavorable environment for dallisgrass seeds to establish. Deep, consistent watering and appropriate fertilization will also strengthen the lawn, allowing it to outcompete and suppress the aggressive weed.