Understanding Dallisgrass: A Persistent Turf Weed

Dallisgrass (Paspalum dilatatum) is one of the most aggressive and resilient perennial grassy weeds commonly found in lawns, sports fields, and agricultural turf across warm climates. Characterized by its rapid clumping growth, deep root system, and prolific seed production, Dallisgrass competes directly with desirable turf species for nutrients, light, and water.

If left unmanaged, this weed can quickly dominate open areas, especially in under-maintained or moisture-retentive soils, resulting in uneven turf surfaces and increased susceptibility to secondary weed infestations. For professional turf managers and home gardeners alike, Dallisgrass poses a significant challenge requiring integrated control measures.

How to Identify Dallisgrass Accurately

Life Cycle and Spread of Dallisgrass

Dallisgrass is a warm-season perennial, which means it regrows year after year and is most active during the warmer months, typically from late spring through early autumn. Its resilience and rapid spread stem from a dual propagation strategy:

• Seed Reproduction: Dallisgrass produces large numbers of seeds that germinate quickly in moist, disturbed soil. These seeds can be spread by wind, water, mowing equipment, and even foot traffic.
• Rhizome Expansion: In addition to seeds, Dallisgrass spreads through short underground stems called rhizomes. These enable the weed to regrow from below the surface even after the top is removed, making it particularly difficult to control through mowing or surface-only herbicide applications.

In poorly drained or overwatered lawns, the combination of seeds and rhizomes allows Dallisgrass to establish thick clusters rapidly and outcompete desirable turf species. This is why an integrated and persistent approach is critical when managing Dallisgrass infestations.

Integrated Management Strategies for Dallisgrass Control

Successfully eliminating Dallisgrass from your lawn requires more than a one-time solution. Due to its perennial nature and dual reproduction system, the most effective control is achieved through an integrated management program that combines physical removal, cultural practices, and carefully selected herbicide treatments.

1. Cultural Practices: Strengthen the Turf to Outcompete Weeds

A dense, healthy lawn is your first line of defense against weed infestation. Implementing the following practices helps reduce Dallisgrass establishment and spread:

• Proper Mowing Height: Maintain turf at its recommended height to maximize canopy density and shade out Dallisgrass seedlings.
• Regular Fertilization: Apply a balanced fertilizer to promote strong root development and robust turf growth.
• Irrigation Control: Water deeply but infrequently to discourage shallow-rooted weed establishment while supporting healthy turf root systems.
• Aeration and Thatch Management: Regularly aerate compacted soil and remove excess thatch, as both create ideal conditions for weed seed germination.

2. Manual Removal: Small-Scale or Early Infestation

For isolated Dallisgrass clumps or early-stage infestations, manual removal is feasible. Carefully dig out the entire plant, including the rhizomes, to prevent regrowth. Avoid composting removed weeds—dispose of them in sealed waste to reduce reseeding risks.

3. Chemical Control: Targeted Herbicide Application

When Dallisgrass is widespread or deeply rooted, herbicide use becomes necessary. Options include:

• Non-Selective Herbicides (e.g., glyphosate): Effective at killing Dallisgrass entirely but will also damage surrounding turf. Best used in spot treatment or during renovation projects.
• Selective Post-Emergent Herbicides: These are preferred for active infestations within established lawns, as they can suppress or kill Dallisgrass without harming most warm-season turfgrasses. Active ingredients such as MSMA (monosodium methyl arsenate) or DSMA (disodium methyl arsonate) are commonly used.
• Pre-Emergent Herbicides: Useful for preventing seed germination. Products based on active ingredients like prodiamine or dithiopyr are effective in disrupting the weed’s lifecycle when applied before soil temperatures rise in spring.

A combination of pre-emergent and post-emergent strategies, applied at the correct times of the year, provides the highest level of control and helps prevent future outbreaks.

Recommended Active Ingredients for Dallisgrass Control

To effectively manage Dallisgrass in turf, pasture, or ornamental landscapes, selecting the appropriate herbicide active ingredient is critical. The right ingredient not only ensures effective suppression or elimination but also minimizes collateral damage to desirable grasses. Below is a breakdown of commonly used active ingredients, categorized by their mode of action and application stage.

1. Non-Selective Herbicide Active Ingredients (Spot Treatment or Renovation Use)

• Glyphosate
  Glyphosate is a systemic, broad-spectrum herbicide that targets virtually all green plants. It is absorbed through foliage and transported to the roots, killing the entire plant. While highly effective against Dallisgrass, glyphosate should only be used for spot treatment or complete renovation, as it can injure or kill turfgrass.
  Application Note: Use a paint-on applicator or shielded sprayer to isolate Dallisgrass.

2. Selective Post-Emergent Herbicides (For Active Infestations in Established Lawns)

• MSMA (Monosodium Methyl Arsonate)
  MSMA is a post-emergent contact herbicide that selectively controls grassy weeds like Dallisgrass in tolerant turf types (e.g., Bermuda grass). It inhibits plant growth through interference with photosynthesis and protein synthesis.
  Use Case: Effective on actively growing Dallisgrass, especially in warm-season turfs.
• DSMA (Disodium Methyl Arsonate)
  Similar in function to MSMA but with slightly different turf safety profiles. DSMA is also used to control sedges and other broadleaf weeds, making it a valuable option in mixed-weed infestations.
  Best For: Turf areas requiring broader selective control under regulated use.

3. Selective Pre-Emergent Herbicides (Preventing Seed Germination)

• Prodiamine
  Prodiamine is a root-inhibiting pre-emergent herbicide. It forms a chemical barrier at the soil surface, preventing Dallisgrass seeds from germinating.
  Timing: Apply in early spring before soil temperatures exceed 13°C (55°F).
• Dithiopyr
  Offers both pre-emergent and early post-emergent activity. It is particularly useful if the application window has been slightly missed, as it can still affect newly germinated seedlings.
  Advantage: Extended residual activity and compatibility with most turfgrass species.

4. Combination Strategies

For persistent infestations, integrating multiple modes of action (e.g., a pre-emergent in early spring followed by a selective post-emergent mid-season) increases success rates and helps prevent resistance buildup. Always follow label instructions and consider rotating active ingredients to reduce herbicide resistance risk.

Dallisgrass Control – Turfgrass Compatibility Chart

Frequently Asked Questions (FAQ) on Dallisgrass Control

Q1: What is the best time to apply herbicides for Dallisgrass?

A:

• Pre-emergent herbicides (e.g., prodiamine, dithiopyr) should be applied in early spring, before Dallisgrass seeds germinate. Ideal timing is when soil temperatures reach 10–13°C (50–55°F) for several consecutive days.
• Post-emergent herbicides (e.g., MSMA, DSMA) are most effective during active growth periods, typically in late spring to early summer, when Dallisgrass is visible and actively metabolizing. Avoid use during drought stress or dormancy.

Q2: Can I apply herbicides without damaging my existing turf?

A:
Yes, if you choose the right selective herbicide. Active ingredients like MSMA or DSMA selectively target grassy weeds while being safe for certain turf types like Bermudagrass. Always check turf compatibility on the product label before application. For areas with mixed or sensitive turfgrass, consider spot treatment with glyphosate or manual removal.

Q3: How long does it take to see results after application?

A:

• Post-emergent herbicides typically show visual yellowing and stunting of Dallisgrass within 7–14 days.
• Pre-emergent herbicides prevent germination, so no immediate visual effect will occur; instead, the benefit is seen in reduced weed emergence over weeks or months.

Q4: Do I need to reapply herbicides?

A:
Yes. Dallisgrass has a deep root system and a strong regrowth capacity.

• Pre-emergents may require reapplication every 3–6 months, depending on the product’s residual period and rainfall.
• Post-emergents may need multiple applications for full eradication, especially for mature clumps.

Q5: Can I combine cultural practices with chemical control?

A:
Absolutely. Integrated Weed Management (IWM) is the most sustainable approach. Combine mowing, proper irrigation, fertilization, and aeration with targeted herbicide application to maximize turf competitiveness and suppress Dallisgrass regrowth.