The sight of perpetual weed growth on your lawn is about as disheartening as it gets.
Do you ever find yourself wishing that you could kill the weeds in your yard before they sprout, and go to seed? Well, you can…
Pre-emergent herbicides give you a way to do just that. Once applied they stay in the soil between one to six months and, if timed and applied correctly, will stop weeds from germinating without killing your grass.
For best results, there are several factors to consider when determining which type of pre-emergent will work best for your lawn type. So I have compiled a pre-emergent herbicide list to simplify the puzzle and help you make the right selection for your lawn.
- How Does Pre-Emergent Herbicide Work?
- Pre-Emergence Herbicide List
- What is the Best Pre-Emergent on the Market?
- When to Apply Pre-Emergent Herbicide
- How to Apply Pre-Emergent Herbicide
- Final Thoughts
- Herbicide List
- FAQ Pre-Emergent Herbicide
The pre-emergent herbicides I’ll cover in this guide include benefin, dithiopyr, isoxaben, prodiamine, and trifluralin.
While these are all pre-emergent herbicides, they don’t all act in the same way. Some chemicals, like benefin, work best for grasses and broadleaf weeds, while others, like pendimethalin, work best in food crop areas.
Read on to learn more about my experience of pre-emergents and hopefully the pre-emergent list below will provide insight and clarity.
How Does Pre-Emergent Herbicide Work?
When applied to soil, pre-emergent herbicides form a chemical barrier in the top layer of soil and prevent seeds from germinating and growing roots. They inhibit a seedling’s ability to perform cell division, therefore killing juvenile sprouts before they ever emerge from the topsoil.
Pre-Emergence Herbicide List
There are several different types of pre-emergent herbicides that work best in different scenarios. I’ll cover five of the most popular types of pre-emergent herbicide active ingredients so that you can make an informed decision on which herbicides will work best for your yard.
Benefin: Great for Established Lawns
Benefin is the active ingredient chemical in pre-emergent herbicides that work exceptionally well for controlling grasses and broadleaf weeds on turfgrasses.
- Ideal for use on established turfgrass
- Kills broadleaf weeds and crabgrass
- Little to no toxicity to humans and mammals
- Toxic to fish
Benefin is the shorthand term for the scientific name Benfluralin. Benfluralin is a dinitroaniline, meaning that it works by inhibiting mitosis in seedlings, which prevents cell division. The lack of cell division keeps roots from developing mature roots and emerging from the topsoil.
Benefin is a great pre-emergent herbicide for controlling broadleaf weeds and grasses. Some of the most widespread weeds that benefin controls include:
- Red clover
- Rye grass
- Seeded alfalfa
- Seeded lettuce
Benefin usually comes in either liquid concentrate form or granule form and is in fact often combined with Trifluralin for use on turfgrass. If using the product in granule form, be sure to water the product after applying it to your lawn. Benefin takes about six hours on average to absorb into the soil. From there, it can begin inhibiting seed growth.
Benefin is a safe pre-emergent herbicide and has a low toxicity level for humans, mammals, and birds. It is toxic to fish, so avoid using products containing benefin if you live near a body of water.
Dithiopyr: Best for Grassy Weeds
Dithiopyr is the active ingredient chemical in pre-emergent herbicides that are especially good for killing crabgrass and oriental grass. Dithiopyr is perfect for use around ornamental plants, ornamental turf, established lawns, non-cropland and industrial sites, and commercial sod farms
- Kills various crabgrass and oriental grasses
- Doubles as an early post-emergent for some species
- Ideal on turfgrass and around ornamentals
- Toxic to fish
- Not great for broadleaf weeds
Dithiopyr works by inhibiting mitosis in a seedling’s roots and inhibiting spindle production, which prevents the plant from developing and maturing.
Dithiopyr is a good option for controlling the growth of different grasses. Some plants that products containing dithiopyr work well on include:
Dithiopyr can even act as a post-emergent herbicide for crabgrass if you apply it to the weed before it tillers.
- Rye grass
- Willow herb
- Wood sorrel
Dithiopyr comes in many forms, including powder, granules, and liquid concentrate for spraying. If using powder or granules, add water to the product after applying it to your lawn so that it can absorb into the soil properly.
Dithiopyr has low toxicity levels for humans, mammals, and birds, but it’s toxic to fish. Avoid using dithiopyr if you live near bodies of water or runoff areas.
Isoxaben: Best for Broadleaf Weeds
Isoxaben is the active ingredient in pre-emergent herbicides that are great for selectively killing broadleaf weeds. Isoxaben is safe to use on turf and around ornamental plants and trees.
- Suitable for ornamentals and turfgrass
- Various forms and concentrations
- Excellent for use on broadleaf weeds
- Not the best for grasses and other weeds
- Moderately toxic
Isoxaben prevents weed growth by inhibiting the production of enzymes needed for protein synthesis within the seed. This ultimately kills the seed before it has the chance to germinate and emerge from the ground.
Isoxaben works exceptionally well for nearly 100 species of broadleaf weeds and grasses, including:
Isoxaben can work as a pre-emergent herbicide for grasses and vines as well.
You will find isoxaben in powder, granule, or liquid concentrate forms. You should water in the herbicide after applying to ensure that it seeps into the soil properly.
Pay attention to the concentration you’re using because isoxaben concentrations in popular herbicides range from just 0.25% up to 75%. The higher the concentration, the longer-lasting the effects will be. Isoxaben can work for as long as eight months with a single application.
Isoxaben has moderate toxicity to humans but can cause chronic harm to small mammals, birds, and fish.
Pendimethalin is one of the most effective active ingredient chemicals for controlling broadleaf weeds and grasses in food crop areas. Useful applications include tobacco fields, potatoes, soybean, corn, and cotton.
- Good for controlling weeds in food crop areas
- Liquid and granule form
- Doubles as a post-emergent for newly-sprouted weeds
- Highly toxic to fish
- Stains hard surfaces
- Cannot reseed until 4 months after use
Pendimethalin is a selective pre-emergent that halts mitosis and inhibits cell growth, preventing target weed seedlings from developing mature roots.
Pendimethalin is an exceptional herbicide for controlling broadleaf and grassy weeds. It’s primarily used to target weeds posing a threat to crop and agricultural areas. In addition to being a pre-emergent herbicide, pendimethalin acts as a post-emergent herbicide for early-stage weeds.
Pendimethalin is available in granular form, but it also comes in liquid concentrate. It’s yellowish and can stain driveways and sidewalks. It can be used to treat a range of broadleaf weeds and grasses including:
Pendimethalin is non-toxic to birds, slightly toxic to humans and mammals, and very toxic to fish. When handling pendimethalin, wear proper safety gear and avoid using near bodies of water. Pendimethalin will not seep into and contaminate groundwater.
Prodiamine: Best for Turfgrasses
Prodamine is one of the most popular and most effective pre-emergent weed killers on this list. It is ideal for use on turfgrasses and around ornamental trees and shrubs. Available as a water-soluble granule or concentrate it controls broadleaf weeds and invasive grasses. However, it is especially effective on crabgrass.
- Cool & Warm-Season turf grasses and lawns, excluding golf putting greens
- Suitable for use around ornamentals and pine trees
- Low staining
- High run-off risk in the event of rain
Prodamine works by preventing root growth by blocking cell division, using it as a pre-emergent over winter is most effective. Safe to use on all turfgrasses such as Bermuda, Fescue, St. Augustine, and most other common turf grasses.
Prevents a broad range of grassy and broadleaf weeds such as:
- Creeping bentgrass
Trifluralin: Best for Flowerbeds and Vegetable Crop
- Great for controlling broadleaf and grassy weeds
- Prevents weed growth on a wide variety of flower and vegetable croplands
- Toxic to fish and potentially a human carcinogen if inhaled
Trifluralin works by stopping mitosis and cell division in the roots of different weeds, preventing the seeds from emerging from the topsoil.
- Annual Bluegrass
- Johnson Grass
Trifluralin controls weeds of various different crops, including broccoli, cabbage, sugar cane, beets, and crops that provide food for animals. You can also use Trifluralin in residential areas to stop broadleaf and grassy weeds from growing around your turfgrass or ornamental plants.
I found Trifluralin in both granule and liquid forms. However, according to my research, it works best when applied as a liquid.
Trifluralin is non-toxic to birds but is highly toxic to fish, and the EPA classified it as a Class C possible human carcinogen. However, the likelihood of the chemical transmitting into the food is very low.
What is the Best Pre-Emergent on the Market?
Different pre-emergents work best for different target weeds. It’s important to research which pre-emergent herbicides will work best for your yard.
Dithiopyr’s ability to handle a wide range of broadleaf weeds and grasses makes it a good choice for turfgrass and lawns. Whilst Trifluralin is preferable for use in flower beds and amongst vegetable crops.
Is There a Natural Pre-Emergent Herbicide?
In place of using a chemical pre-emergent herbicide, use corn gluten meal as a natural alternative.
Corn gluten meal is a byproduct of corn milling and contains no synthetic chemicals. When applied to yards and watered in, corn gluten meal can prevent broadleaf weeds and grassy weeds from sprouting.
Corn gluten meal remains in the soil for up to six weeks and reapplying a couple of times a year will help to ensure its effectiveness.
When to Apply Pre-Emergent Herbicide
Applying a pre-emergent at the right time is almost as crucial as determining which herbicide will target your weeds.
Different pre-emergent herbicides work in different ways. Most of the ones on our list only work once the seed has sprouted before emerging from the soil. If applied too early, the herbicide can drain from the soil before the seed begins to sprout, so your yard could be covered in weeds despite your efforts.
As a rule of thumb, pre-emergent herbicides should be applied to the soil once it begins to reach and maintain temperatures around 55 degrees Fahrenheit. Specific application times vary based on your location.
What Month To Use Pre-Emergent?
You should apply pre-emergent herbicides twice a year, once in the early spring and then in the early fall. The specific month varies based on your location, but for most temperate climates, apply in early March and then again in late August or early September.
When is It Too Late for Pre-Emergent?
Applying pre-emergent herbicides too late is the most common reason that a pre-emergent doesn’t work. If you apply a pre-emergent too late for example, when temperatures have exceeded 55 degrees Fahrenheit, the seeds will have already rooted and sprouted, and you will need to look into post-emergent herbicide methods for removal instead.
How to Apply Pre-Emergent Herbicide
Different types of pre-emergent herbicides need to be applied in different ways. The primary forms of pre-emergent herbicides are granules, liquids, and powders.
When applying a granule or powder, you can use a grass seeder to evenly cover your yard. Hit all the spots to avoid possible weed growth. When you use granule or powder herbicides, water them afterward so they can soak into the topsoil.
If you opt for a liquid herbicide, you prepare it according to the package and use a backpack or handheld sprayer of your choosing to evenly coat your yard. Furthermore, water your yard after applying a liquid pre-emergent so it can soak into the soil properly.
How Often Should You Apply Pre-Emergent?
It varies based on the product, but most pre-emergents work for up to 6 months. You should apply pre-emergent at least twice a year for optimal results.
Does Pre-Emergent Herbicide Need to Be Watered In?
Yes, pre-emergent herbicides should be watered immediately after application to soak into the soil and create a protective chemical barrier.
This article has covered my best pre-emergent herbicide list and how to use these herbicides for your yard based on my research and experience.
When choosing a pre-emergent, keep in mind what your target weeds will be and what type of land you are using herbicide on.
Common pre-emergent ingredients in bold font:
- 2,4-D amine
- Capric acid
- Clomazone Clopyralid
- Metam sodium
- Pelargonic acid
- Quizalofop p-ethyl
FAQ Pre-Emergent Herbicide
Now that we’ve covered the most popular pre-emergent herbicides and how to use them, you may have some questions. Below are the most frequently asked questions about pre-emergent herbicides.