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…
Preventative herbicides give you a way to do just that. Once applied, they stay in the soil between up to 6 months and, if timed and applied correctly, will stop weeds from germinating without killing your grass.
For the best results, there are several factors to consider when determining which type of treatment 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.
- Benefin: Great For Established Lawns
- Dithiopyr: Best For Grassy Weeds
- Isoxaben: Best For Broadleaf Weeds
- Prodiamine: Best For Turf Grasses
- Trifluralin: Best For Flowerbeds And Vegetables
- How Often Should You Apply Preventative Herbicide?
- Does Pre-Emergent Herbicide Need To Be Watered In?
The herbicides I’ll cover in this guide include benefin, dithiopyr, isoxaben, prodiamine, and trifluralin.
While these are all preventative herbicides, they don’t all act in the same way. Some chemicals, like benefin, work best on grasses and broadleaf weeds, while others, like pendimethalin, work best on food crop areas.
How Does Pre-Emergent Herbicide Work?
When applied to soil, these herbicides form a chemical barrier in the top layer of soil that prevents 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.
Common Active Ingredients
There are several different types of pre-emergent herbicides that work best in different scenarios. Here’s some information about some of the most popular 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 in many herbicides designed for controlling grassy and broadleaf weeds on turf grasses.
- Ideal for use on established turf grass
- Kills broadleaf weeds and crabgrass
- Little to no toxicity to humans and mammals
- Toxic to fish
Benefin is the shorthand term for Benfluralin. Benfluralin is a dinitroaniline, meaning that it works by inhibiting mitosis in seedlings, which prevents cell division. The lack of cell division keeps seedlings from developing mature roots and emerging from the topsoil.
Benefin is a great ingredient 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 often combined with Trifluralin for use on turf grass. If using the product in granule form, be sure to water 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 generally considered safe 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 an active ingredient that is especially good for killing crabgrass and oriental grass. Dithiopyr is perfect for use on 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 turf grass 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. Dithiopyr can even act as a post-emergent herbicide for crabgrass if you apply it to the weed before it tillers.
Some plants that products containing dithiopyr work well on include:
- 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 an active ingredient that selectively kills broadleaf weeds. Isoxaben is safe to use on turf and around ornamental plants and trees.
- Suitable for ornamentals and turf grass
- 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 preventative treatment 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 ingredients 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 herbicide 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, 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.
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 Turf Grasses
Prodamine is one of the most popular and most effective weed killers on this list. It is ideal for use on turf grasses 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. It’s safe to use on all turf grasses, 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 Vegetables
Trifluralin is a selective herbicide that works best on annual grasses and broadleaf weeds in flower beds and amongst vegetable crops.
- 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. It’s effective on:
- Annual Bluegrass
- Johnson Grass
Trifluralin controls weeds found in 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 turf grass or ornamental plants.
I’ve 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 food is very low.
What Is The Best Weed Prevention On The Market?
Different pre-emergents work best for different target weeds. It’s important to research which herbicides will work best for your yard and its most common weeds.
Dithiopyr’s ability to handle a wide range of broadleaf weeds and grasses makes it a good choice for lawns. Whilst Trifluralin is preferable for use in flower beds and amongst vegetable crops.
Is There A Natural Weed Preventer?
In place of using a chemical herbicide, you can also use corn gluten meal as a natural weed preventative.
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. Reapplying a couple of times a year will help to ensure its effectiveness.
When To Apply Pre-Emergent Herbicide
Applying a herbicide at the right time is almost as crucial as determining which active ingredient will best target your weeds.
Different herbicides work in different ways. Most of the ones I’ve mentioned only work once the seed has sprouted but before it emerges 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, preventative 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 Weed Preventers
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 herbicides too late is the most common reason they don’t work. If you apply a weed preventer 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 herbicides for removal instead.
How To Apply Pre-Emergent Herbicide
Different types of preventaitve herbicides need to be applied in different ways. The primary forms 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 herbicide so it can soak into the soil properly.
How Often Should You Apply Preventative Herbicide?
It varies based on the product but most pre-emergents work for up to 6 months. You should apply preventative herbicides at least twice a year for optimal results.
Does Pre-Emergent Herbicide Need To Be Watered In?
Yes, some herbicides should be watered immediately after application to soak into the soil and create a protective chemical barrier. Check the product label to determine the best watering practices for your chosen formula.
This article has covered my list of top active ingredients to look for in weed preventers and how to use these herbicides for your yard based on my research and experience.
When choosing an herbicide, always keep in mind what your target weeds will be and what type of land you are using herbicide on.
Pre-Emergent Herbicide List
Most common active ingredients in bold font.
- 2,4-D amine
- Capric acid
- Clomazone Clopyralid
- Metam sodium
- Pelargonic acid
- Quizalofop p-ethyl