Maintaining a healthy St Augustine lawn means controlling stubborn weeds without harming your turf. Post-emergent herbicides target weeds that have already germinated, while some products also offer pre-emergent benefits to prevent future germination. This guide reviews five well-regarded options that perform reliably on St Augustine, describing what they treat, how to apply them safely, and key considerations for choosing the right product for your lawn. Always follow label instructions and local regulations when applying any herbicide.
| Product | Active Ingredient(s) | Best For | Application Note |
|---|---|---|---|
| Syngenta Tenacity | Mesotrione | Broadleaf and grassy weeds; seedings | Pre- and post-emergent control; safe on many turfgrasses |
| Petra Mesotrione Concentrate | Mesotrione | Weed prevention and control in new and existing lawns | Post- and pre-emergent capabilities; broad weed spectrum |
| Monterey Grass Getter | Sethoxydim-based | Selective control of grassy weeds | Over-the-top application; not for lawn use |
| Lawn Synergy Three-Way | Multiple broadleaf weed active ingredients | Broadleaf weed control; professional strength | Fast-acting; suitable for landscapes and beds |
| Southern Ag Atrazine | Atrazine | Crabgrass and other common lawn weeds | Includes surfactant for better coverage |
Choosing the right post-emergent herbicide depends on your lawn’s specific weed pressures, whether you’re overseeding, and how tolerant your turf is to certain chemistries. The products listed below are selected for their compatibility with St Augustine grass and their ability to manage a mix of broadleaf and grassy weeds. When possible, combine products with good cultural practices—proper mowing height, irrigation, and seasonal overseeding—to maximize effectiveness and reduce recurrence of weeds.
Syngenta Tenacity Post Emerge Weed Control
Product overview: Syngenta Tenacity is a versatile herbicide labeled to control a broad spectrum of weeds, including crabgrass, dandelion, clover, yellow nutsedge, and more. It functions as both a pre-emergent and post-emergent control, which can be advantageous for St Augustine lawns facing a mix of weed pressures. Tenacity is designed to suppress new weed germination while actively targeting existing plants, helping preserve the turf you want to keep. Its flexible timing supports overseeding and bare-ground seeding, making it useful during lawn renovations as well as maintenance.
How it works: Tenacity contains mesotrione, a naturally occurring compound that interferes with plant growth. When applied to actively growing weeds, it disrupts photosynthesis and growth in susceptible species, leading to targeted control with minimal impact on many turfgrasses when used as directed. The product’s label provides a list of tolerant turf varieties, which is essential guidance for St Augustine homeowners.
Application considerations: For best results on St Augustine, apply Tenacity according to the label’s timing windows and mixing directions. It can be used to treat existing weeds and during seeding or overseeding activities, but it requires careful calibration to avoid harming desirable turf. Pay attention to water requirements after application, including any restrictions on irrigation or rainfall that could affect absorption. The product’s broad weed spectrum makes it suitable for mixed weed pressures common in warm-season lawns.
Pros & considerations: Flexible use with seedings; effective on broadleaf and grassy weeds; mindful of turf tolerance. Always test on a small lawn area first if you’re unsure about turf compatibility, and monitor regrowth in the weeks following treatment. Tenacity is a strong choice when you want a single product that can serve both preventive and curative roles in a St Augustine lawn.
Petra Mesotrione Weed Killer Concentrate
Product overview: Petra’s Mesotrione-based weed killer is positioned as a post- and pre-emergent option for new and existing lawns. It targets stubborn weeds and is marketed as a broad-spectrum solution for lawn care, including control of common weeds that challenge St Augustine lawns. The concentrate form provides the flexibility to mix for smaller areas or scale up for larger lawns, depending on the label’s dilution instructions.
How it works: Like Tenacity, Petra relies on mesotrione to disrupt cell processes in susceptible weeds. The product’s effectiveness depends on timing and coverage, particularly for pre-emergent use to prevent germination of annual weeds and for post-emergent control of established plants. The label typically enumerates a range of weeds covered, along with any turf tolerance notes.
Application considerations: This option is suitable if you’re managing a lawn with persistent crabgrass, clover, or other common turf weeds. Follow mixing instructions to achieve even coverage, and avoid applying during temperatures or conditions that could stress the turf. As with other mesotrione products, proper identification of target weeds is important to maximize selectivity and reduce risk to desirable grasses.
Pros & considerations: Flexible application timing; strong weed spectrum; suitable for both new and established lawns. Always adhere to label directions for rate and interval between applications, and consider integrating with cultural practices to reduce weed pressure over time.
Monterey Grass Getter (Sethoxydim)
Product overview: Grass Getter is a selective post-emergent herbicide designed to target grassy weeds, including crabgrass and foxtail, among others. It is applied as a spray over the top and is suitable for use in landscapes containing ornamentals and shrubs, not typically for direct lawn use. This makes it more appropriate for weed control in garden beds and non-lawn areas where grassy weeds are present among ornamentals, rather than a pure lawn treatment for St Augustine grass.
How it works: Grass Getter acts as a systemic herbicide that is absorbed by the foliage and moves to the root system, effectively killing targeted grasses while minimizing damage to broadleaf plants. It’s particularly useful when grassy weeds have invaded beds or mixed plantings near a lawn edge, helping to maintain surrounding plant health while reducing grass competition.
Application considerations: Because it is not designed for lawns, use Grass Getter with caution around lawn turf species and ensure you apply only to the intended areas. Protect surrounding ornamentals and avoid overspray onto turf where not intended. Check the label for any restrictions on application areas and timings that align with your landscape plan.
Pros & considerations: Strong grassy weed control in mixed plantings; suitable for edging and beds; not a primary lawn-only solution. For St Augustine lawns, rely on products labeled for turf when targeting lawn weeds to avoid unintended turf injury.
Lawn Synergy Three-Way Post Emergent
Product overview: Lawn Synergy Three-Way is a post-emergent selective herbicide designed to deliver fast-acting control of broadleaf weeds. It is described as professional strength and is positioned for use in landscapes that require rapid kill of broadleaf species. For St Augustine lawns facing broadleaf infestation, this product can be a strong option when precision is needed to minimize impact on the turf while targeting weeds such as dandelion and clover.
How it works: The product relies on a blend of active ingredients that disrupt various physiological processes in broadleaf weeds. The systemic action helps move the herbicide through the plant, leading to rapid visible effects and reduced regrowth in treated areas. The formulation is optimized for broadleaf suppression in landscapes and beds that contain mixed plantings.
Application considerations: Follow label directions for dilution, coverage, and timing. Because this is a post-emergent, ensure you are targeting the intended weed species and avoid application during periods of high heat or drought that could stress desirable plants. Consider mowing height and irrigation practices after application to support recovery of desired turf.
Pros & considerations: Fast acting on broadleaf weeds; strong professional-grade performance; suitable for landscapes and beds. Not specifically optimized for dense St Augustine turf weed complexes, so use with turf-specific products when broadleaf pressure is high in the lawn itself.
Southern Ag Atrazine Lawn Weed Killer
Product overview: Southern Ag Atrazine is a widely used weed killer that provides suppression of driveway, lawn, and garden weeds, with an emphasis on grassy and some broadleaf species in St Augustine lawns. The product includes a non-ionic surfactant to enhance coverage and penetration, which can improve weed kill efficiency in warm-season grasses. Atrazine is a classic tool for homeowners managing crabgrass and related weeds in lawns and is often used in combination with good cultural practices.
How it works: Atrazine disrupts photosynthesis in susceptible weed species, effectively reducing growth and eventually leading to weed death. It is absorbed through the leaves and moves systemically throughout the plant. The product’s effectiveness depends on proper timing and coverage, along with environmental conditions during and after application.
Application considerations: Atrazine products require careful handling, particularly around water runoff and sensitive vegetation. Always follow the label for application rates and drift precautions. Use a surfactant as recommended to improve penetration, especially in dense turf areas where weed leaves may be harder to reach. Avoid using on stressed or recently seeded areas if the label restricts compatibility.
Pros & considerations: Time-tested weed control option with broad applicability in lawns and landscapes; surfactant improves performance. It’s important to understand local regulations and environmental considerations when using Atrazine, as restrictions can apply in certain regions.
Buying Guide: Post Emergent Weed Control For St Augustine
Key considerations help you select the right post-emergent herbicide for St Augustine grass and ensure effective, safe results. This guide outlines critical factors, including weed spectrum, turf safety, application timing, and integration with cultural practices.
- Weed spectrum and target species: Identify the predominant weeds in your lawn (broadleaf vs. grassy weeds). Some products excel at broadleaf control, while others focus on grassy weeds. If your lawn has a mix, a product with broad-spectrum activity or a combination approach (pre- and post-emergent) can be advantageous.
- Turf safety and labeled use: Always verify that the product is labeled for use on St Augustine grass. Some formulations are better suited for ornamental beds or mixed landscapes and may not be appropriate for turf.
- Application timing: Post-emergent herbicides are most effective when weeds are actively growing. For ongoing weed issues, staged applications in the right season optimize control while reducing stress on the lawn.
- Seeding and overseeding considerations: If you plan to overseed or reseed patches of bare soil, choose products labeled for use around existing or new seedings. Some herbicides allow application during seeding, while others require avoiding newly sown areas for a specified period.
- Mode of action and resistance management: Rotate herbicides with different modes of action to minimize the risk of weed resistance. Consider pairing a post-emergent with a pre-emergent strategy for long-term control.
- Environmental and safety considerations: Be mindful of weather, irrigation restrictions, and near water sources. Follow all label directions to minimize potential harm to non-target plants and the environment.
- Tank mixing and compatibility: If using multiple products, check compatibility and label directions for mixing. Some products may interact in ways that reduce effectiveness or increase the risk of turf injury.
- Long-term lawn health: Combine chemical controls with cultural practices—correct mowing height for St Augustine, adequate irrigation, and proper fertilization—to strengthen turf and reduce weed establishment over time.
In practice, a homeowner managing St Augustine weeds benefits from having at least two primary options: a broad-spectrum post-emergent for general weed suppression and a selective herbicide for targeted grasses or stubborn weeds. When possible, consult local extension resources or a turf professional to tailor your approach to your climate, soil, and weed pressure. Regular lawn maintenance—mowing at the correct height, deep and infrequent irrigation, and timely overseeding—can significantly reduce the need for repeated herbicide applications.
Note: This article provides informational guidance and product summaries based on publicly available product descriptions and labels. Always read and follow the current label and local regulations before applying any herbicide to your lawn.