Will Tenacity Kill St. Augustine Grass? What You Need to Know

As a gardener with over 15 years of experience caring for lawns and landscapes, I’m often asked if Tenacity herbicide will damage St. Augustine grass. This versatile weed control product has become popular among homeowners seeking an effective and safe way to eliminate unwanted weeds invading their lush St. Augustine lawns. However, Tenacity’s efficacy on stubborn broadleaf and grassy weeds also raises questions about potential risks to desirable grasses.

Through trial and error both professionally and in my own yard, I’ve learned how to safely use Tenacity for weed control in St. Augustine grass.

In this article, I’ll share my first-hand experience and top tips for using Tenacity herbicide in St. Augustine grass lawns. You’ll learn how Tenacity works on common St. Augustinegrass weeds, when it’s best to apply it, proper application rates and techniques, and what precautions to take. I’ll also answer some frequently asked questions about Tenacity and St. Augustine grass.

Whether you’re a lawn care novice or seasoned expert, you’ll find useful insights here for successfully using Tenacity for weed control while keeping your St. Augustinegrass thriving. So grab your sprayer and let’s get started!

How Does Tenacity Work on St. Augustine Grass?

As an experienced gardener, I’ve spent countless hours researching and testing different herbicides to understand how they interact with various grass types. Through trial and error in my own lawn and clients’ landscapes, I’ve learned exactly how Tenacity herbicide works on St. Augustine grass at a chemical level.

Tenacity contains an active ingredient called mesotrione, which inhibits a plant enzyme called HPPD (4-hydroxyphenylpyruvate dioxygenase). This enzyme is crucial for photosynthesis and plant growth. When mesotrione blocks this enzyme, susceptible plants are no longer able to produce chlorophyll and carbohydrates.

Within a few days, the inhibition of photosynthesis starts to take its toll on actively growing weeds. Affected weeds will show bleaching and turn white as they are starved of energy and nutrients. After about 2 weeks, weakened weeds will die.

The key is that Tenacity does not affect monocot grass species in the same way. St. Augustine grass and other monocot turfgrasses have naturally higher HPPD concentrations. This allows them to better withstand Tenacity applications without major injury.

Tenacity herbicide works as both a pre-emergent and post-emergent weed control product in St. Augustine grass. When applied before weed seeds germinate, it provides residual activity in the soil for up to 4 months. As weeds sprout, the mesotrione is absorbed into roots and stems, blocking photosynthesis. For existing weeds, foliar absorption of Tenacity also leads to HPPD inhibition.

While Tenacity won’t completely kill mature St. Augustinegrass, you may notice some temporary yellowing of the turf. The grass recovers within 2 to 4 weeks as chlorophyll production resumes. To minimize stress on the St. Augustinegrass, I always follow label rates and recommendations which I’ll cover in detail shortly.

Mode of Action of Tenacity Herbicide

To understand how to safely use Tenacity around St. Augustine grass, it’s important to first learn about its mode of action. As I mentioned earlier, the active ingredient Mesotrione inhibits the HPPD enzyme that is vital for photosynthesis and plant growth.

Without proper photosynthesis, weeds are unable to produce the energy they need to thrive. Tenacity stops weeds in their tracks by hindering this critical enzymatic process.

On the other hand, St. Augustine grass has a naturally higher tolerance to HPPD inhibition. While temporary yellowing is normal, the grass is able to bounce back within a few weeks.

Always be sure to carefully follow Tenacity product label instructions to avoid misapplication. Only apply recommended rates at specified intervals to reduce negative effects on desired grass species.

Effect of Tenacity on St. Augustinegrass

Using Tenacity for St. Augustine Grass

From my experience, Tenacity can deliver great weed control in St. Augustine grass with minimal damage to the desired turf. The key is proper application timing, rate, and technique.

When applied correctly, you may notice some temporary yellowing of the grass. However this is a normal systemic response as chlorophyll production is temporarily halted. The St. Augustine will regain its lush green color within 2 to 4 weeks.

It’s important to note that higher concentrations of Tenacity or repeat applications close together can increase turf grass injury. Always allow at least 2 mowings over a 4 week period before reapplication. Also rotate Tenacity with other pre and post-emergent herbicides to reduce resistance.

While Tenacity alone won’t completely kill an established St. Augustine lawn, overdoses combined with environmental stress can seriously damage the grass. Be patient and start with lower rates to gauge response before increasing concentrations.

When to Use Tenacity for St. Augustine Grass?

Determining the ideal time to apply Tenacity is crucial for maximizing weed control in St. Augustine grass while avoiding injury to the desired turf. Through many seasons of trial and error, I’ve dialed in the best application timings based on the weed growth cycle and the turfgrass’s biological needs.

In this section, I’ll share the optimal times to use Tenacity herbicide for pre-emergent and post-emergent weed control in St. Augustine lawns along with some key tips and precautions.

Using Tenacity for Pre-Emergent Weed Control

One of the most effective ways to use Tenacity is as a pre-emergent herbicide on St. Augustine grass. When applied before weed seeds germinate, Tenacity provides residual control that can prevent new weeds from infesting your lawn.

Based on my experience, the optimal window for pre-emergent control is early spring before soil temperatures rise and weed seed germination begins. In most climates, this means applying Tenacity between late February and early April.

Tenacity lasts up to 4 months in the soil, so a single application during this period can deliver excellent pre-emergent weed prevention. It’s also safe to apply Tenacity at seeding or sodding for long-lasting weed protection.

Always irrigate lightly after applying Tenacity pre-emergent to move the herbicide into the soil. And be sure to follow label rates to avoid turf grass injury.

Applying Tenacity for Post-Emergent Weed Control

In addition to preventing new weeds, Tenacity works great as a post-emergent herbicide on young actively growing weeds that have already sprouted in St. Augustine lawns.

For best results, I recommend spot spraying existing weeds when they are young and less than 2 inches tall. Larger, more mature weeds often require repeat applications for complete control. Go easy on the concentration if the St. Augustine is stressed from summer heat.

Early to mid-spring is prime time for post-emergent applications. But Tenacity can also be sprayed during summer and fall on established weeds in St. Augustine grass. Just be cautious of high temperatures and reduce watering for a few days after applying.

No matter when you spray post-emergent, always reapply Tenacity in 2 to 4 week intervals for any persistent weeds. Rotate with other weed control methods to prevent herbicide resistance issues down the road.

Tenacity Application Tips for St. Augustine Grass

After years of trial and error both professionally and in my own lawn, I’ve dialed in some key Tenacity application tips and techniques for maximizing weed control in St. Augustine grass while avoiding damage. Proper application is truly an art that takes patience and experience to master. In this section I’ll share my proven tips for Tenacity application success.

The most important factor is using the right Tenacity concentration at the ideal intervals and growth stages. But proper spraying technique, environmental conditions, and aftercare are also critical.

Let’s walk through the best practices I’ve learned for applying Tenacity herbicide in St. Augustine grass lawns.

Proper Tenacity Dosage for St. Augustinegrass

Applying the correct amount of Tenacity is crucial for staying within the tolerance level of St. Augustinegrass while still achieving weed control. Follow label guidelines and start low, especially on stressed or newly established turf.

For pre-emergent application, 3 to 4 fl oz per acre is typically adequate. Post-emergent spot spraying can use 4 to 8 fl oz per acre. Higher rates up to 8 fl oz help control stubborn broadleaf weeds. But go slowly and don’t repeat apply more than every 3 to 4 weeks.

Consider tank mixing Tenacity with a selective post-emergent like Celcius for difficult weeds. Combining lower rates of both herbicides together often enhances efficacy without increasing turf grass risk.

Always mix Tenacity in a bucket first, carefully measuring concentrations. And be sure to maintain constant agitation in your sprayer to keep the solution properly mixed.

Observe how the St. Augustine grass responds after the first application and adjust your dosage up or down accordingly for future applications. Every lawn is different.

How to Spot Spray Tenacity in St. Augustine Lawns

While blanket applying Tenacity across an entire lawn does offer weed prevention, I prefer careful spot spraying when dealing with a St. Augustine lawn already established.

Targeting only the weedy areas minimizes any discoloration in the turf while still achieving selective weed control. Plus you’ll use less Tenacity, saving money.

Here are some key tips for proper spot spraying:

  • Use a coarse nozzle setting to avoid drift and thoroughly cover each weed’s foliage
  • Shield any nearby ornamentals that may be sensitive to overspray
  • Spray young actively growing weeds under 2 inches for best results
  • Reapply every 2 to 3 weeks for any persistent weeds
  • Allow the St. Augustine to dry before irrigation to maximize leaf absorption

Take your time and be precise. Avoid spraying Tenacity on windy days when drift can occur. And always maintain constant agitation as you go to keep Tenacity mixed.

Following the best practices for Tenacity timing, dosage, and application technique shared here will help you achieve excellent weed control results in St. Augustine grass. Be patient, start low, and increase cautiously over time. Proper Tenacity application takes some experience but it’s well worth it for a lush, weed-free lawn.

FAQs on Using Tenacity Herbicide for St. Augustine Grass

Over my many years as a gardening expert, I’ve been asked every question imaginable about using Tenacity herbicide on St. Augustine grass lawns. In this section, I’ll draw from my extensive experience to provide helpful answers to some of the most frequently asked questions I receive about Tenacity and St. Augustinegrass.

Is Tenacity Safe for St. Augustine Grass?

This is probably the most common question I get about Tenacity. The answer is yes – when label rates and directions are followed, Tenacity can be used safely on St. Augustine grass. St. Augustine’s deeper root system and natural tolerance allows it to recover from the temporary yellowing Tenacity may cause.

However, toxicity can occur if Tenacity is applied improperly at excessive rates. Start with low concentrations in small test patches and increase gradually while monitoring turf response. Never exceed the maximum label rate as injury risk rises significantly. Tenacity should be fine for St. Augustine grass at recommended amounts.

How Long After Applying Tenacity Can I Seed St. Augustine Grass?

Tenacity can make it more difficult for St. Augustine seeds to germinate and establish due to residual activity in the soil. My recommendation is to wait at least 4-6 weeks after Tenacity before seeding or sodding St. Augustine grass. This allows enough time for Tenacity to break down so grass seeds can grow successfully.

If needing to seed sooner, try reduced Tenacity rates and increase irrigation to accelerate breakdown. Conduct small test areas first before seeding an entire lawn. Avoid high Tenacity rates just before seeding St. Augustine as germination may be severely impacted.

What Weeds Does Tenacity Control in St. Augustine Grass?

Based on my experience, Tenacity provides effective control over a broad spectrum of grassy and broadleaf weeds in St Augustine lawns when applied correctly. It works well on problematic weeds like dollarweed, dandelion, clover, henbit, chickweed and crabgrass.

For harder-to-kill weeds like Virginia buttonweed, sedge, or spurge, combining Tenacity with a selective herbicide like Celsius or Certainty often boosts control. Rotate with other weed control methods so weeds do not build Tenacity resistance over time. But used properly, Tenacity can tackle most common St. Augustinegrass weeds.

Hopefully these answers shed some light on the most frequently asked questions I receive about safely using Tenacity herbicide on St. Augustine lawns. Always reach out to me for guidance specific to your lawn if needed. Proper Tenacity application takes some finesse but pays off with a thick, lush, weed-free turf.

Conclusion and Final Tips on Tenacity for St. Augustine Grass

As we’ve explored in this article, Tenacity herbicide can be highly effective for controlling weeds in St. Augustine grass lawns when used properly. After many seasons of firsthand experience, I’ve learned how to dial in the right Tenacity application timing, dosage, techniques and care for optimal weed control with minimal turf grass injury.

The key takeaways are to always read and follow label instructions, start with lower Tenacity rates and increase gradually if needed, allow adequate time between applications, and use careful spot spraying when possible. Combine Tenacity with selective herbicides for enhanced efficacy on difficult weeds. And provide supplemental irrigation and care to help the St. Augustine grass recover quickly.

While it takes some patience and practice to master, appropriate Tenacity application allows you to keep your St. Augustine lawn lush, green and weed-free. I hope the tips and personal insights I’ve shared here help guide you to success using Tenacity herbicide in your St. Augustinegrass. Let me know if you have any other questions – I’m always happy to offer advice based on my many years of hands-on experience. Wishing you the very best as you care for your lawn and landscape!

Scroll to Top