Dallis grass (Paspalum dilatatum) is a persistent, warm-season perennial weed. This aggressive grass forms unsightly clumps in lawns, competing with desirable turf for water and nutrients. Its deep, fibrous root system and ability to produce copious amounts of seed make eradication difficult, often requiring a multi-faceted approach. This guide provides a comprehensive strategy for identifying, removing, and preventing the return of this weed.
Recognizing Dallis Grass
Dallis grass is easily identifiable by its coarse, clumping growth habit, which stands out distinctly from finer turfgrasses. The leaf blades are wide, typically ranging from a quarter to a half-inch in width, and possess a prominent midrib. Unlike many other weeds, the base of the stems may exhibit a purplish tinge, and the leaf sheaths are often slightly flattened.
The most distinctive characteristic is the seed head, which emerges on a tall stalk that quickly outgrows the surrounding lawn. These terminal stalks feature three to five or more spike-like branches, or racemes, that are widely separated and appear to droop slightly. The seeds, or spikelets, are hairy, oval, and paired along the axis, contributing to the plant’s prolific spread.
As a perennial, Dallis grass survives the winter using its deep root system and short, thick rhizomes. This life cycle makes it resistant to simple annual weed control methods, requiring the mature plant to be killed, not just emerging seedlings. The plant thrives in moist conditions, and its ability to rapidly produce seeds ensures new infestations are always a risk.
Non-Chemical Removal Methods
For small, isolated patches of Dallis grass, manual removal is a viable, non-chemical solution that minimizes damage to the surrounding lawn. Hand-pulling alone is often insufficient due to the plant’s deep, fibrous roots and tough rhizomes, which may leave root fragments behind. It is more effective to use a shovel or spade to dig out the entire clump, ensuring the entire root crown and all underground stems are removed.
This physical removal is easiest when the soil is moist, allowing the dense root ball to be lifted completely. For slightly larger areas, solarization can be employed after removing the tops of the plants down to the soil line. Covering the area with clear or black plastic for several weeks uses the sun’s heat to kill the remaining root system and any dormant seeds in the soil.
Cultural controls reduce the weed’s vigor and spread. Maintaining a higher mowing height for desirable turfgrass encourages a dense canopy that shades the soil. This shading naturally suppresses the germination of Dallis grass seeds and prevents new seedlings from establishing. Consistently mowing before the weed produces its distinctive seed heads also prevents the plant from adding to the soil’s seed bank.
Effective Herbicide Strategies
Chemical control requires the use of selective post-emergent herbicides. Since Dallis grass is a perennial, the active ingredients must be systemic, meaning they are absorbed by the leaves and transported down to kill the extensive root system. A single application is rarely sufficient to eradicate the mature plant, and multiple treatments are necessary for complete control.
Herbicide Selection
Professional-grade selective herbicides containing active ingredients such as Mesotrione, Quinclorac, Monument, Celsius, and Certainty are effective options. The choice depends heavily on the type of turfgrass present. Some products, like Mesotrione, can damage certain grasses like zoysiagrass or bentgrass. Homeowners should check product labels carefully to ensure compatibility with their specific lawn type before application.
Application Timing
The timing of application influences the success of the chemical strategy. Herbicides are most effective when Dallis grass is actively growing and translocating nutrients, typically during late spring through summer.
Fall applications, when air temperatures begin to drop below 72°F, are particularly effective. This is because the plant is actively moving resources to its roots for winter storage, carrying the herbicide with it.
Application Method
For maximum effectiveness, the first post-emergent application should be followed by a second treatment four to six weeks later. Spot-treating individual clumps is preferred over a broadcast application, as it minimizes the amount of chemical applied to the desirable turf. Non-selective herbicides like glyphosate can be used for spot treatments, but they will kill all vegetation they contact, requiring reseeding or sod replacement in the treated area.
Preventing Future Infestations
Long-term prevention relies on a two-pronged strategy: using pre-emergent herbicides and promoting dense, healthy turf. Pre-emergent herbicides create a chemical barrier in the soil that prevents germinating seeds from developing. While they will not kill existing perennial plants, they are essential for managing the high volume of seeds left behind by mature weeds.
Application timing depends on soil temperature, not the calendar date. Dallis grass seeds begin to germinate when soil temperatures consistently reach the 60°F to 65°F range, typically in early spring. Applying the product before this threshold is reached is necessary for maximum effectiveness. Products containing active ingredients like dithiopyr are effective options for this preventive step.
Dense turf naturally outcompetes Dallis grass seedlings for light, water, and nutrients. This requires deep, infrequent watering to encourage a strong, deep root system in your turfgrass. Proper fertilization based on soil testing and consistent mowing at the correct height will maintain the vigor and density needed to resist re-infestation.