6 Best Pre-Emergent Herbicides For Lawns- How To Apply Pre-Emergents

Weeds — regardless of which type are a nightmare for any lawn or garden, and can create havoc in even the most meticulously maintained lawns! This is why applying a pre-emergent herbicide at the right time of year will keep these unwanted weeds from growing in the first place.

Below I’ll introduce what a pre-emergent does as well as list some of the best pre-emergent herbicides on the market today (along with best use cases).

I like to think of weeds as cockroaches — the noticeable ones are only the tip of the iceberg, and there are many more hidden just waiting for their right time to grow. These pesky plants have innate characteristics that let them spread easily. 

As they plague your lawn, weeds compete with your lush grass and garden plants for space, sunlight, water, and other essential soil nutrients. 

They continue to rob your favorable plants of their health and also turn into the perfect hosts for disease and insects, allowing pests such as grubs to gain a foothold before your favorable plants take flight. 

Getting rid of weeds after an infestation isn’t easy, and the best way to prevent them is by applying the right solutions before they even take root, which you can do with pre-emergent herbicides.

Pre-emergent herbicides are a chemical option to stop weeds from growing in the first place and are formulated to target specific types of weeds and/or their families. 

What is a Pre-Emergent? 

Herbicides are an effective solution in your battle against annual, perennial, and biennial weeds. 

Pre-emergent herbicides, just as the name suggests are chemical compositions that are used on established lawns to prevent the emergence of weeds.

When properly applied, pre-emergent herbicides serve as a backbone for your weed control efforts and are highly effective in getting rid of the most common lawn weeds.  

How do Pre-Emergent Herbicides Work? 

Pre-emergents don’t prevent weed seeds from germinating, and work only after the weed seeds have germinated. 

Therefore, when applied, pre-emergents will not kill all the seeds present in the soil, but will only kill the ones that have germinated. 

Once a weed seed germinates, a primary root emerges from the seed, which is the part that absorbs the pre-emergent that was sprayed on the soil surface, killing the weed seed. 

What’s important to note is that pre-emergent herbicides are highly un-soluble, so you want the active ingredient to stay at or very near to the soil surface, because this is the area where most weeds tend to stay and germinate. 

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6 Best Pre-Emergents for Your Lawn 

These are the products that I use most often. Each has its pros and cons which I’ll go over below.

1) Dimension 2EW

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Dimension 2EW is a liquid selective pre-emergent herbicide that provides powerful control of grasses and broadleaf weeds in your lawn. It contains 24 percent of the active ingredient dithiopyr and is available in 1/2 and 2.5-gallon jugs.

Dimension 2EW is best applied before the weeds begin to crop up, and will not get rid of weeds that have already established, except for crabgrass in its early stages of growth. 

How to use Dimension 2EW? 

To use Dimension 2EW, you will need a backpack or handheld sprayer, and some PPE for your safety such as glasses, gloves, and a mask. 

1. Calculate the square footage of the area you want to treat (length x width = square footage).
2. You can mix 0.5 to 0.73 per 1,000 sq ft with one gallon of water depending on the weed. Refer to the product label for the exact rates per weed. 
3. Fill half of the sprayer with water, then add the Dimension 2EW, and any spray dye or surfactant. Adding a surfactant reduces the surface tension of the spray droplets, increases spray retention, and allows the liquid to reach a larger area. Here are some of the other benefits of a surfactant.
4. Close the lid to your sprayer tight, gently agitate the container, fill the rest of the container and agitate one more time, and spray on the area you’d like to treat for weeds.

The best time to use Dimension 2EW is when the weeds are visible and begin to germinate, which is generally between February to May in northern states, and between January to March in southern states. 

2) Tenacity

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Tenacity serves as a systemic pre-emergence and post-emergence herbicide and offers residual control of weeds in turfgrasses. It is absorbed by weeds as they emerge from the soil, and is not recommended for use on Bermudagrass or St. Augustine lawns. 

This herbicide contains 40 percent of the active ingredient Mesotrione and lasts for approximately 30 days when used as a pre-emergent. 

Tenacity can help control over 40 different types of weeds including southern crabgrass and buttercup, and prevents photosynthesis in plants and keeps them from growing. 

How to apply Tenacity pre-emergent herbicide? 

A small eight-ounce bottle of Tenacity is enough to control weeds spread across one to two acres of property. You also get a syringe along with the bottle to use for spot pre-emergent herbicide treatments. 

1. Mix four to eight ounces of Tenacity with at least thirty gallons of water per acre, and apply it with a surfactant like Southern Ag Surfactant to increase its effectiveness. 
2. Another application may be needed after two to three weeks for adequate weed control. 

3) Snapshot

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Another highly effective selective pre-emergent, Snapshot contains Isoxaben (0.5%), Trifluralin (2%) active ingredients, and should be applied at the rate of 2.3 to 4.6 lbs per 1,000 square foot. 

It can control several different types of weeds including crabgrass, annual bluegrass, and clover, and works around the clock for roughly six to eight months. 

Snapshot bonds tightly with the soil particles, and is low in water solubility, so it won’t wander away out of the application zone. 

How to apply Snapshot? 

1. Snapshot can be applied in early spring at the rate of 2.3 to 4.6 lbs per 1,000 square feet.
2. Following the first application, monitor the weed control over time, and reapply if needed.

4) Surflan AS

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Surflan AS functions as a selective pre-emergent herbicide that controls a myriad different tough weeds including large crabgrass, foxtail, annual bluegrass, and much more. 

It contains 40 percent of the active ingredient oryzalin and is safe to use on warm-season turfgrasses including Bermudagrass, Buffalo grass, Centipede, Zoysia, and even sensitive grass types such as St. Augustine. Wondering how oryzalin works?

Surflan AS lasts up to four months when applied at 1.5 ounces per 1000 square feet and can be used on non-bearing trees and vines, landscape ornamentals, and established warm-season turf. 

When applied properly, Surflan AS can deliver up to eight months of weed control, making it a preferred choice for many lawn owners.  

How to use Surflan AS? 

1. Fill a sprayer with to about 3/4^th with water, and then mix in Surflan AS at the rate of 1.5 – 3 ounces per 1000 square feet. 

2. Put the sprayer on the fan setting for uniform coverage, and spray over the problem areas of your lawn. 

3. Reapply as needed. 

You should always wear safety equipment during use. And also remember to keep pets and kids away from the treated area until the chemical has dried. 

5) Prodiamine 65 WDG (Wettable Dispersible Granule)

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If you’re looking for a granular pre-emergent, Prodiamine 65 WDG is hard to beat! It arrives in a non-dusty granular formation, making it easy to dissolve when mixed with water in a sprayer. 

This flexible and effective pre-emergent herbicide can be applied in both the spring and fall and apart from crabgrass, controls spurge, bluegrass, witchgrass, and much more. 

Prodiamine 65 WDG can be used safely on several common turfgrasses including Bermudagrass, Fescue, and St. Augustine, and can be mixed with fertilizer and iron solutions before application. 

Prodiamine 65 WDG will not kill any new grass that is actively growing but shouldn’t be applied over freshly planted ornamental plants. 

As its name suggests, it contains 65 percent of the active ingredient Prodiamine and must be applied before the weeds start germinating. 

How to use Prodiamine 65 WDG? 

Before using Prodiamine 65 WDG, you have to determine a few things including the size of your yard, the recommended dose for that size area, and the amount of water to evenly cover your lawn. 

1. You can spray Prodiamine 65 WDG using either a backpack or handheld pump sprayer. 

2. After you determine the square footage of the area you’d like to treat, you can apply anywhere between 0.185 ounces to 0.83 ounces per 1,000 square feet per year. 

For example, the recommended rate to treat Crabgrass in a 2000 square feet turf is between 0.72 to 1.66 ounces in one gallon of water. 

3. Fill your sprayer roughly a ¼ of the way with water or fluid fertilizer, agitate the container a bit, add the right dose of Prodiamine 65 WDG, and then the remaining amount of water. 

4. Set the spray nozzle of your sprayer on fan mode for even coverage, and begin spraying over the weed-ridden areas of your yard. 

6) Crabgrass Control .37% Prodiamine Herbicide

Crabgrass Control .37% Prodiamine is a high-quality lawn fertilizer that also works as a selective pre-emergent herbicide for the control of grass and broadleaf weeds. It features 37 percent of the active ingredient Prodiamine and is made from 100 percent potash.

Crabgrass Control can be ordered in a large 50 lbs bag and can cover up to 12,500 square feet. It is effective at controlling several different types of weed including crabgrass, quackgrass, bluegrass, carpetweed, and chickweed, and should be applied at the rate of 2.7 pounds per 1,000 square feet. 

How to use Crabgrass Control .37% Prodiamine?  

1. Refer to the herbicide application rates on the label, and mix accordingly with water. 

2. Calibrate the sprayer, and spray generously over the weed-affected area. 

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How to Choose the Best Pre-Emergent Herbicide for Your Lawn? 

Determining the best pre-emergent for your lawn is as easy as identifying the weeds your lawn is plagued with, and then finding the weed killer that can bring the problem under control.

If your lawn is generally weed-free in the summer but riddled with winter annual weeds such as stinkweed, flixweed, and shepherd’s purse, then you need to apply a fall pre-emergent herbicide. 

Contrarily, if your yard is free of weeds in the winter, but loaded with summer-weeds such as crabgrass, then you need to buy spring pre-emergent herbicide. And if you have year-round weed problems — congratulations, you need them both. 

Pros and Cons of Using Pre-Emergent Herbicides 

Learning about the advantages and disadvantages of pre-emergents will help you decide whether this type of weed control treatment is right for your lawn. 

Why You Should Use a Pre-Emergent to Prevent Weeds

• Eliminates weeds before they form and permanently – one of the biggest advantages of using a pre-emergent herbicide is that you get rid of the weeds before they grow. 

Apart from pre-emergent herbicides, there are myriad other types of weed control methods, but the downside to these is that they kill the weeds after they’ve sprouted and after they’ve caused a fair amount of damage to your yard. 

Pre-emergents work after the weed seed is allowed to germinate and kill young tender sprouts, permanently eliminating the weed. Further, pre-emergent herbicides are activated in the top layer of the soil, where the weed sprouts, hence breaking the cycle of constant regrowth. 

• Quickly covers a large yard – one of the other great advantages of pre-emergent applications is their ability to cover a larger area of your yard. If you have a large lawn and don’t use a pre-emergent herbicide, you will spend countless hours trying to get the weeds out. 
• Use now, use less later – the good thing about using a pre-emergent herbicide at the right time is that you get rid of most if not all the weeds that have germinated. This means that you will have to use less pre-emergent each successive season. 

When You Shouldn’t Use a Pre-Emergent to Prevent Weeds

• Should be applied at the right time – timing is key to the success of your pre-emergent application. Remember, pre-emergents are formulated to kill weeds after they germinate, but the herbicide will not be able to do its job if applied at the wrong time. 
• Keep kids and pets off the lawn – given that pre-emergents are in essence chemical formulations, you will have to keep your kids and pets off the yard for at least 24 – 48 hours after application. 

If you have pets that go to the bathroom outside, keeping them off the lawn for this period may be a challenge.

What Are The Active Ingredients in Pre-Emergent Herbicides?

Not all pre-emergents will kill all types of weeds. For example, pre-emergents that are formulated to eradicate broadleaf weeds will not perform the same for dreaded crabgrass, because it’s a grass!

Here are some of the common active ingredients in pre-emergent herbicides that are used in most leading products. 

Isoxaben

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Isoxaben is a broad-spectrum per-emergent herbicide active ingredient that does a great job at keeping broadleaf grasses, weeds, and vines at bay. It has a musty odor and is available in water-dispersible powders, granules and liquid concentrates. 

This broad-spectrum pre-emergent ingredient can deliver up to eight months of control, which means that you can keep weed issues in check for almost all year long. 

Isoxaben only targets the problem weeds and causes no harm to your desired plants, but is not effective at controlling weeds that have already germinated or are firmly established. 

Simazine

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Simazine is a pre-emergent chemical ingredient that is proven to control woody plants as well as annual and perennial grasses and broadleaf weeds. It has an impressive residual effect between 3 months to 6 months and is mainly used in croplands and vineyards. 

Apart from controlling weeds on turfgrass, Simazine also works well to control aquatic weeds such as algae and submerged weeds. 

Oxyfluorfen

Another effective pre-emergent chemical ingredient to kill annual and grassy broadleaf weeds, Oxyfluorfen is a preferred choice for controlling weeds in residential areas, particularly those that creep up on porches, patios, sidewalks, and other areas. 

It is a versatile pre-emergent chemical ingredient in that it can be used as both a pre-emergent and post-emergent herbicide. 

When used as a pre-emergent, Oxyfluorfen can control annual grasses such as crabgrass and other broadleaf plants, and as a post-emergent controls annual ryegrasses and broadleaf weeds including wild mustard and pigweed. 

Prodiamine

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Many homeowners believe that weeds such as crabgrass die as soon as temperatures drop in the winter, but this isn’t the end of the ordeal. Crabgrass seeds stay alive in lawns in the winter, indulge in the nutrients of the soil, and emerge in the spring. 

Prodiamine is a highly recommended pre-emergent herbicide that kills crabgrass and other stubborn weeds before they rise from the soil. 

It can be safely used on certain types of desirable turf grasses without harming them including Fescue, Bermudagrass, and St. Augustine. 

Oryzalin 

Oryzalin is an active ingredient used in several pre-emergent herbicides and looks like a bright yellowish-orange powdery substance. It is mainly used for controlling annual grasses and broadleaf weeds, and on residential and commercial/industrial lawns and turf. 

Dithiopyr

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Dithiopyr is an active ingredient found in many popular pre-emergent products. It can control many different types of weeds but works especially well for preventing crabgrass from popping up in the spring. 

Dithiopyr is a pre-emergent and a post-emergent for crabgrass only and is safe to use on most cool-season and warm-season grasses. It is clear in color, has virtually no odor, and offers a wider window for application.  

Granular vs. Liquid Pre-Emergents – Which is Better?

Pre-emergents are available in both granular and liquid formulations and are referred to as ‘foliar’ weed control methods because they have to be absorbed by weeds through their foliage (leaves). 

Whether you choose a granular or liquid pre-emergent herbicide, herbicide distribution is extremely important for effective and efficient weed control.  

A liquid pre-emergent can be distributed over your entire much more easily, evenly and precisely, while using less product compared to a granular pre-emergent. 

Liquid pre-emergents are also easier to store in a shelf or storage cabinet, but on the downside, you’ve got to measure and mix it water and agitate before application. 

Even though we’re talking about just a few minutes, what holds people back is the fear that they’re going to over-mix or undermix the liquid pre-emergent herbicide. 

With liquid pre-emergents, you also have to avoid spraying on windy days, because the last thing you want is for the herbicide to drift to areas that you’ve overseeded or freshly seeded. 

Granular pre-emergents are ready to go right out of the box, so all you’ve got to do is empty the bag in a spreader, and off you go! Liquid pre-emergents can be applied on wet or dry weeds, making them a much more versatile option. 

But granular pre-emergents work best when they stick to wet weeds because, without the surface moisture, the granules will roll off the weeds, resulting in ineffective control. 

And given that the chances of rain are unpredictable, irrigating the lawn can be a daunting task to say the least. All in all, wet and dry pre-emergent herbicides have the potential to control the entire weed including the root when applied properly. 

Liquid pre-emergents are a go-to choice for most professional lawn care providers, simply because they are absorbed by the weed’s leaf surface, and don’t require moisture to stick to the leaf. And once they dry, they stay on the surface of the weed leaves even if it rains. 

However, if you’re looking for a D.I.Y. method to control weeds in your yard, and have the time and patience to apply the pre-emergent when the lawn is wet, then granular pre-emergent herbicides are perhaps a great option.

When is the Best Time to Apply Pre-Emergent Herbicide? 

The first thing to understand when applying any type of pre-emergent herbicide is that a single application is never enough to eliminate weeds in your yard. 

There is no silver bullet that kills all weeds because all weeds have different lifecycles and methods of reproduction. 

Weed seeds are hardy per se, given that they can stay dormant for years, surviving a fire, drought, and several pre-emergent herbicide applications. 

Even if you’re lucky enough to get rid of all the weeds from your property, there’s always a good chance they can return through wind, water, animals, or human activity. 

When it comes to the best time to apply weed, two different schools of thought come into play. 

The Scientific Method

The scientific method of determining when to apply pre-emergents entails monitoring weather patterns and taking soil temperature readings. You get the soil temperature info for your state by simply searching “soil temperatures in [your state]” in Google. 

If you’re going to apply pre-emergent herbicide in the spring, then you should wait until the soil temperature reading is around 55 degrees F for 36 hours or so. 

This gives you the right amount of time to set up your pre-emergent barrier before the weeds begin their skyward path. 

For wintertime application, spray or spread the pre-emergent when the temperatures are around the mid-70s for five days straight. 

The Early Bird Gets the Worm Method 

The scientific method is the best way to determine the right time to apply pre-emergents, but not everyone has the time to monitor weather patterns and soil temperatures. 

Pre-emergent herbicides do their job regardless of the time you apply them, so the earlier you apply them in the season, they will kill the weeds before they ever see the light of day.  

Applying the Right Amount of Pre-Emergent Herbicide

Using granules or liquid formulations are the two main ways to apply pre-emergent herbicides. 

Regardless of which one you use, it’s very important that the herbicide penetrates the soil surface during the initial application, and not get trapped by grass and other plants. 

How to Apply Granular Pre-Emergent Herbicides? 

Before you apply a granular fertilizer to your yard, you will have to calculate the square footage of the area you’re looking to treat. You can do this easily by measuring and multiplying the length of the area by the width (length x width = square footage). 

Next, read the label on the pre-emergent to gauge the amount of herbicide to apply per 1000 square feet. Calibrate your spreader to get better, and consistent results when the product is applied accurately. 

Once calibrated, walk across your lawn in two passes in a grid-like fashion until your lawn is covered. After you’ve covered the entire yard area with the granular pre-emergent, do not mow the lawn until you’ve watered the chemical or it has rained. 

The active ingredient in the pre-emergent granular herbicide will be trapped in the granule until it’s activated by water. 

How to Apply Liquid Pre-Emergent Herbicides? 

Start by mixing the pre-emergent herbicide according to the directions on the label in a sprayer, and spray the product evenly across your yard. 

Why Didn’t My Pre-Emergent Application Work? 

Pre-emergent herbicides can be highly effective in controlling weeds in your lawn if used properly. But sometimes may not work due to several reasons, most notably: 

• Timing of application – most weed seeds germinate at roughly 50 degrees F, but may have already germinated in case of an early spring warm-up or delayed application. 

Further, soil in certain areas may warm up faster than others such as concrete walkways or a south-facing slope, causing the weeds to germinate faster than the surrounding areas, resulting in ineffective weed control. 

• Coverage or quantity – not all pre-emergent herbicides are the same, where coverage amounts do vary, which is why it’s important to read the manufacturer label to determine the right amount of herbicide for your treatment area. 

For example, if you have to cover a 5000 square feet area, using the amount to cover three thousand square feet won’t work “almost as well”. 

It is also critical that you avoid “lumpy” applications, which is a good reason you should invest in a spreader, and spread the pre-emergent in a grid-like pattern. 

• Mechanical interference – even if you apply the pre-emergent herbicide correctly, and at the right time, mechanical interference can put a hole in your virtual weed mat. This includes mole activity, children or pets playing on the lawn, or any other such mechanical interferences. 
• Re-application is needed – most pre-emergents are generally effective for three months or so, but this time can be shortened due to environmental factors. 

Sun and rain can degrade most chemicals including pre-emergents, so apply the pre-emergent before heavy rain is predicted, and plan a reapplication within the next three months after the first one.  

Myths About Pre-Emergent Herbicides Busted

Most lawn owners know that if they want to control weeds, a pre-emergent application is needed. But when looking for answers about how pre-emergents work and how to apply pre-emergents, there are quite a bit of commonly-held fallacies that crop up. 

#1 You don’t have to apply a pre-emergent if you haven’t had prior weed issues

Many “misinformed” lawn care professionals claim that there’s no longer a need to apply a pre-emergent herbicide if you’ve managed to control weeds for the past few years. 

But as mentioned earlier, weed seeds can be transported great distances by wind, animals, and even humans, so it’s best to treat your yard each year. 

#2 You don’t have to treat thick lawns

While this might hold, because lush, thicker lawns are better at shading the soil surface to reduce weed germination, your lawn may thin out during the summer due to stress such as drought and may invite weeds. 

#3 Soil aeration should be avoided during pre-emergent control

This depends on the type of aeration, because core aeration removes a large amount of soil from the ground, whereas tine aeration disrupts a small amount. 

Even though it’s advisable not to deliberately aerate after applying pre-emergent applications, it won’t cause too much harm if you need to. 

Final Thoughts

Pre-emergent herbicides tackle weeds before they grow, and post-emergent herbicides work to control weeds after they have germinated. So, if you already see weeds in your lawn, then it’s too late to apply a pre-emergent herbicide. 

These herbicides can be applied to your lawn in the spring and fall, but it’s important that you diligently read the label to determine the right application rates for the type of weeds you’re looking to control, and the square footage of your lawn.  

Sources:

• NC State Lectures 5 & 6 Preemergence Herbicides
• Michigan State Timing Crabgrass Preemergence Applications
• Kansas State Premergents