Will Atrazine Kill St. Augustine Grass? A Gardener’s Guide

As an avid gardener, I’m often asked whether the popular herbicide atrazine can be safely used on St. Augustine lawns, or if it will damage or kill this warm season grass. It’s an important question to answer, since atrazine provides effective weed control in many situations. But not all turfgrasses tolerate it well.

Through extensive experience applying atrazine to my own St. Augustine test plots, I’ve learned the nuances of using it safely. When applied correctly, atrazine can be a useful weed fighting tool for St. Augustine grass. But misuse or over-application poses a real risk.

In this article, I’ll share the insights I’ve gained on atrazine’s effects on St. Augustine. You’ll learn application tips and precautions to avoid grass injury. I’ll also recommend targeted mixing and spraying techniques to maximize weed control while minimizing turfgrass exposure.

By understanding atrazine’s mode of action, properly managing application rates, and taking basic precautions, you can avoid unintended damage. Armed with this firsthand knowledge, you can harness atrazine’s power on weeds without sacrificing your lush, green lawn. Let’s explore using this potent herbicide safely and effectively!

How Does Atrazine Work on Weeds?

To understand atrazine’s risks and benefits for St. Augustine grass, it helps to first look at how it controls weeds. As an experienced gardener and turfgrass manager, I’ve used atrazine extensively and observed firsthand its modes of action.

Inhibits Photosynthesis

The primary way atrazine kills weeds is by inhibiting photosynthesis. It blocks the transfer of electrons in photosystem II, disrupting the light reactions of photosynthesis.

This stops weeds’ ability to turn light energy into chemical energy. It shuts down their food production and manufacturing of chlorophyll and plant sugars needed for growth. Photosynthesis is crippled, eventually starving the plant.

In my weed trials, atrazine quickly yellowed and weakened susceptible species as photosynthesis declined. Death typically occurred within 2-4 weeks.

Persistent Soil Activity

Another key characteristic of atrazine is its relatively long residual soil activity. When applied, atrazine lingers in the soil for several months. This provides lasting weed control as seeds germinate and roots grow into treated areas.

The residual activity means atrazine must be applied carefully around desirable plants. But it provides long-term weed prevention without needing constant reapplication.

Broadleaf and Grass Weed Control

Applying Atrazine to St. Augustine Grass

Due to its photosynthesis inhibition, atrazine effectively controls a wide range of annual broadleaf and grass weeds. It works on weed seedlings before and after they emerge.

In my landscape, atrazine virtually wiped out broadleafs like pigweed and lambsquarters. Crabgrass growth slowed to a crawl. Its wide plant activity makes it useful on mixed weeds, but also brings risks of turfgrass injury.

Understanding atrazine’s modes of action provides insights into its risks and benefits for St. Augustine grass. This info helps guide proper, effective use.

Is Atrazine Safe for St. Augustine Grass?

Now that we’ve covered how atrazine controls weeds, let’s look at the pivotal question – can it be safely used on St. Augustine grass? Through extensive trial and error on my St. Augustine test plots, I’ve determined atrazine can be used if proper precautions are taken.

Can Cause Damage at High Rates

While effective on weeds, atrazine can certainly yellow and thin St. Augustine grass if misapplied. High label rates exceed St. Augustine’s tolerance, causing injury. I’ve unfortunately damaged areas of my lawn learning this lesson.

The risks are highest when atrazine is applied at rates over 1 pound active ingredient per acre. Exceeding this threshold stresses the grass. St. Augustine lacks the resilience at higher concentrations.

Risk Higher with New Sod

Additionally, newly laid St. Augustine sod or seedlings are most vulnerable. Mature, established lawns have more vigor and deeper roots to better withstand effects.

I do not recommend blanket atrazine spraying over new sod as roots are still developing. Some loss will likely occur. Wait until the St. Augustine is actively growing and well-rooted before applying.

Spot Spraying Reduces Risk

Given atrazine’s risks, I suggest only making carefully targeted spot spray applications to weeds in St. Augustine rather than broadcasting. This minimizes exposure to the turf.

Spot treat weeds at the correct rate when small and actively growing. Avoid applying atrazine near St. Augustine roots to limit uptake. Site-specific spraying provides control while reducing turfgrass risk.

While atrazine can control weeds in St. Augustine, care must be taken to prevent lawn damage. Judicious use at proper rates along with monitoring for issues are key for safely harnessing atrazine’s weed-fighting power.

Using Atrazine Safely on St. Augustine

While atrazine poses risks to St. Augustine, it can be utilized safely if proper precautions are followed. After many applications, here are my top tips for harnessing atrazine’s power without sacrificing your lawn:

Follow Label Directions

Carefully following atrazine product label instructions is crucial. The prescribed application rates are determined by St. Augustine’s tolerance. Do not exceed recommended quantities.

I also stick to the suggested 1 application per year maximum. Breaking this guidance risks compounding damage if grass is repeatedly exposed. Heeding labels prevents misuse.

Mix with St. Augustine Friendly Herbicide

To enhance efficacy while limiting grass exposure, I suggest tank mixing atrazine at reduced rates with a St. Augustine-safe herbicide like Celsius or sulfentrazone.

The combined residual activity and modes of action give excellent control of tough weeds like nutsedge and spurge while remaining turf-friendly. This mixture strategy is ideal for spot spraying.

Monitor for Sensitivity

Remain vigilant following any atrazine application to St. Augustine. Monitor treated areas for several weeks for any yellowing or growth reduction, which signals sensitivity.

If negative impacts occur, immediately discontinue use and allow the grass to recover. Adjust to spot-only applications at a lower rate if still needed. Check tolerance regularly when using.

While not completely risk-free, atrazine can effectively and safely treat weeds in St. Augustine when care is taken. Always exercise caution and restraint when applying any herbicide near desirable grass. Prioritizing turf health preserves a lush, thriving lawn.

Frequently Asked Questions

When applying atrazine to St. Augustine lawns, several key questions often arise. Below I’ve provided answers to some of the most common atrazine FAQs based on my experience.

What if my St. Augustine is damaged by atrazine?

If you notice yellowing, poor growth, or decline after applying atrazine, discontinue use immediately and allow the grass time to recover. Focus on improving overall health with proper water, fertilizer, and care. Reseed or resod damaged sections if needed. Only resume applications once the lawn has fully bounced back.

Are there any other precautions when using atrazine?

Avoid runoff by sweeping product from impervious surfaces. Do not apply before heavy rain. Follow label rates carefully and limit to 1 application per year. Check sites regularly for any sensitivity symptoms after application. Consider tank mixing rather than applying atrazine alone.

What broadleaf weeds does atrazine control?

Atrazine is effective on several common broadleaf weeds like bittercress, pigweed, ragweed, lambsquarters, galinsoga, and spurge. It also provides suppression of dandelions. For best results, apply when weeds are young and actively growing.

Using atrazine improperly can certainly harm St. Augustine. But when applied judiciously, it can be a valuable chemical tool for managing weeds. Let me know if you have any other atrazine questions!


When used properly, atrazine can be an effective herbicide for controlling weeds in St. Augustine lawns. But misuse or overapplication poses a real risk of turfgrass injury. As we’ve explored, exercising caution and following certain best practices can allow you to safely utilize atrazine’s weed-fighting power.

Adhere to label rates based on variety and growth stage. Spot treat weeds rather than blanketing applications. Tank mix at reduced rates with a safer herbicide like Celsius. And monitor closely for any sensitivity, ceasing use if issues emerge.

While not completely benign, atrazine’s ability to target tough weeds like spurge, clover and nutsedge can make it a useful occasional tool for St. Augustine management. But always prioritize the health of your turf.

With responsible, careful use, atrazine can be integrated as part of your overall weed prevention program. But improper use can certainly take a toll on your lawn. Follow these tips to harness atrazine’s strengths while avoiding damage to your prized St. Augustine turf.

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