Dallisgrass is a highly invasive, perennial weed that poses a significant challenge when it infests an established Bermuda grass lawn. The difficulty in controlling this specific weed arises because both Dallisgrass and Bermuda grass are warm-season grasses, meaning they share the same active growing season and similar biology. Many common herbicides that target weeds in cool-season lawns would also severely damage the Bermuda grass. Successfully removing Dallisgrass requires a comprehensive, multi-step strategy that combines chemical treatments for immediate control with cultural practices for long-term prevention.
Identifying Dallisgrass and Understanding its Persistence
Dallisgrass is a coarse-textured, grayish-green grass that grows in distinct, unattractive clumps rather than spreading uniformly like healthy Bermuda grass turf. A mature clump can be identified by its short, thick rhizomes, which are underground stems that allow the plant to root quickly and spread. The plant’s most recognizable feature is its seed head, which grows tall and stands out above the mowed turf. These seed heads consist of several spikes arranged along a central stem, often featuring distinctive black spots on the seeds. Dallisgrass is a perennial, meaning it returns year after year from its root crown and rhizomes. This perennial nature, combined with its prolific seed production, makes Dallisgrass difficult to eradicate, demanding complete removal of the root system or the use of systemic herbicides.
Selective Post-Emergent Chemical Strategies
Chemical control is the most effective method for established Dallisgrass infestations, requiring selective post-emergent herbicides that target the weed without damaging the Bermuda grass. Timing is critical, as the weed must be actively growing to absorb the herbicide effectively. This period occurs in late spring to early summer when soil temperatures reach 60 to 65 degrees Fahrenheit.
Monosodium Methyl Arsonate (MSMA) is a selective herbicide historically used for Dallisgrass control. MSMA is highly effective on actively growing Dallisgrass, though its use is now heavily restricted and often limited to commercial applications, such as on golf courses. Where permitted, multiple applications spaced 10 to 14 days apart are usually necessary for good control.
Homeowners must rely on other selective herbicides, primarily those from the sulfonylurea class of chemicals. Active ingredients such as foramsulfuron and sulfosulfuron are effective options for suppression and control in Bermuda grass. Foramsulfuron is often applied as a spot treatment, sometimes requiring sequential applications every 7 to 14 days for the best results.
The most effective approach often involves a rotation or mixture of these selective herbicides. Combining sulfonylurea herbicides with an oil-based surfactant is recommended to enhance absorption into the coarse leaf blades of the Dallisgrass. Spot treatment, applying the herbicide only to the Dallisgrass clumps, is preferred over broadcast application to minimize the risk of injury to the surrounding Bermuda turf.
Non-selective herbicides like glyphosate must be used with extreme caution because they will kill any green plant tissue they contact. These broad-spectrum products are only suitable for very localized spot treatments, often using a shielded sprayer or paint-on applicator to prevent drift. Alternatively, glyphosate can be applied during the narrow window in late fall when Bermuda grass has gone completely dormant but the Dallisgrass leaves are still green.
Non-Chemical and Mechanical Removal Techniques
Mechanical removal is a viable non-chemical strategy, particularly for addressing small or isolated clumps of Dallisgrass. Because the plant is a perennial with short, thick rhizomes, it is necessary to dig out the entire root crown and all attached rhizomes. Hand-pulling is most effective when the soil is moist, which helps ensure the entire root system is removed.
If any part of the perennial root crown or a rhizome fragment is left behind, the Dallisgrass plant will likely regrow. Digging creates a void in the lawn that must be immediately filled with soil and reseeded or sodded with Bermuda grass. Failure to fill the void allows Dallisgrass seeds or other opportunistic weeds to colonize the exposed soil.
For slightly larger, concentrated patches, solarization can be used as a non-chemical spot treatment. This technique involves covering the infested area with clear plastic sheeting during the hottest part of the year. The trapped solar heat raises the soil temperature high enough to kill the Dallisgrass plants and their seeds, preparing the soil for replanting once the solarization period is complete.
Long-Term Cultural Practices to Prevent Re-infestation
Maintaining a dense, healthy Bermuda grass lawn is the most effective long-term strategy for preventing Dallisgrass re-infestation. A vigorous turf canopy shades the soil, which helps to suppress the germination of Dallisgrass seedlings. Bermuda grass should be mowed frequently and kept at the lower end of its recommended height, typically between 1 and 1.5 inches, to promote density and aggressive lateral spread.
Proper watering techniques are important for encouraging deep, robust Bermuda grass root systems that can outcompete shallow-rooted weeds. The lawn should be watered deeply but infrequently, soaking the root zone rather than using light, daily sprinklings. This practice discourages the shallow root growth favored by Dallisgrass while strengthening the desirable turf.
A consistent fertilization schedule promotes the aggressive spread of Bermuda grass, allowing it to quickly fill in any gaps where Dallisgrass might try to establish. Applying a high-nitrogen fertilizer during the growing season encourages the lateral growth of the Bermuda grass stolons. By creating an environment where the desired turf is thick and healthy, the lawn becomes a hostile environment for Dallisgrass seeds and newly germinated seedlings.