How Long Does It Take For Atrazine To Work?

how long does it take for atrazine to work

Atrazine takes about 15 to 20 days to kill a weed. It takes so long for the weed killer to work because the toxin must first be absorbed through the roots into the leaves. Once it travels into the leaves, it can begin inhibiting photosynthesis, ultimately starving the plant to death.

If you’re constantly wrestling with weeds in your yard, this chemical can help eradicate and prevent them from growing.

How to Use Atrazine

Atrazine is a popular herbicide that you can use to spruce up your lawn. Since atrazine is a fairly controversial chemical, it’s important to know how to handle it safely. We’ll walk you through the basics of how to apply atrazine properly, including when and how to spread it.


Unlike more basic weed sprays, you’ll want to watch your weather conditions for the best time to apply this product to your lawn. The right time to start spreading atrazine is when the temperature is between 65-90°F. Do not apply it when the temperature is over 90°F since the weed killer won’t be as effective at that heat. Atrazine should be used on dry ground.

If it has rained within 2 or 3 days of when you’re planning to apply it, you’ll need to reschedule. An overwatered lawn can actually make the weed killer less effective.


Atrazine comes in a concentrated form. If you were to use it straight from the container, it would be a serious overload for your grass. To prepare what you need for your lawn, you’ll be mixing the chemical with plain water. Follow the directions on the product label closely and know your lawn’s dimensions before you begin. For every  500 sq. ft. area, 4.3 fl. oz. of atrazine will need to be combined with one gallon of water.

Do not mix atrazine with another weed killer. Since atrazine is considered a surfactant product, you won’t need to add another product to make it more effective. It should be able to handle the job on its own.


You should always use protective gear when spraying this chemical on your lawn. In fact, direct contact with the herbicide can be dangerous. You should be focusing your atrazine only grass weeds or broadleaf weeds.

The weed killer will get rid of the plants that are already growing along with those that are still in their seed form. After applying it, atrazine will not need to be watered in.

Wait to water the area where you applied the weed killer for 7 to 10 days after your initial treatment. You can spray up to twice a year to keep the weeds under control. This can also help you knock out anything that may have been missed in the first application.

Pro Tip
The best time to apply atrazine is when the lawn or weeds are slightly damp, but not overly wet.

Is Atrazine Safe?

At this time, there is no concrete proof that atrazine is harmful to humans. If any atrazine does get into your system, it takes about 24-48 hours to leave your body through the urine or feces.

Even though it does an efficient job killing your weeds, it’s effects have been under close scrutiny. There has been some research showing that when certain levels are found in water, the chemical can actually be deadly to small animals such as frogs, bees, and birds.

Atrazine doesn’t seem to accumulate in living organisms like algae, clams, or fish. Because of this, atrazine doesn’t seem to build up in the food chain.

Here are a few safety precautions to take:

  • Do not have pets in the area when you are treating the weeds.
  • Keep pets away from treated areas until the surfaces are completely dry.
  • If you do have any direct contact, make sure to contact your local Poison Control.

DON’T MISS: Learn the difference between atrazine and simazine in our article here.

Frequently Asked Questions:

How long does atrazine last?

Once Atrazine is applied to the weed and soaks into the soil, it can remain there for several days to several months. In most cases, the atrazine will be present in the ground for one growing season. After that, it will be mostly broken down.

How long does atrazine need to be sprayed before a rainstorm?

You need to apply atrazine at least 1 hour before it rains in your area for the best application and absorption.

How often can you apply atrazine?

You should only apply atrazine twice a year. If you live in a warmer area, most experts recommend that you put the first application on in January, so the weeds do not have time to recover from winter. The second application should be made in November when the harvest is done, and there are seeds in the air.

However, if your area happens to have a shorter growing season, you’ll want to wait until any snow is completely melted off the ground before you apply the first application. And, again, you should make the second application after your typical harvest time is over.

How does atrazine work?

Atrazine kills the weeds by preventing photosynthesis. The weeds’ roots will soak up the weed killer. The chemical will then travel into the tips of any leaves that are actively growing. There will be some absorption through the leaves, but it’s not enough to kill the weed until it has gone through the roots first.

You might be wondering how the herbicide will affect your other plants. After all, you don’t want to ruin the rest of your beautifully cultivated lawn. It’s true, Atrazine is absorbed by all plants. However, the plants that atrazine does not kill breaks down the chemical before it can affect the photosynthesis process.

Pro Tip
You can mix atrazine with 2-4-D and liquid fertilizer, just perform a compatibility test first to check for unwanted changes in color, odor, or consistency. 


Keeping your lawn green and pristine can be a tough job — those weeds never seem to never stop. But as long as you use the right product and do regular applications, keeping annoying weeds under control shouldn’t be a difficult task any longer. Follow the tips and directions and let atrazine keep your yard in control.

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