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Pre-Emergent Herbicides

February 1, 2024 | Categories: ,
close-up of Crabgrass

When it comes to turf management—whether you’re a golf course superintendent, sports turf manager, or lawn care professional—weeds and nuisance grasses often stand in the way of picture-perfect turf. Enter pre-emergent herbicides, which are the best weed control tool in your arsenal. In this blog post, we’ll explore what pre-emergent herbicides are, how they work, and the best practices for their application.

Understanding the ins and outs of pre-emergent herbicides is essential for maintaining a healthy and vibrant landscape. Let’s dive in:

What is Pre-Emergent Herbicide?

Pre-emergent herbicides, often referred to as weed preventers or pre-emergent weed killers, are a crucial component of weed control strategies. Unlike post-emergent herbicides that target existing weeds, pre-emergents act as a “barrier” to prevent weed seeds from germinating. This barrier inhibits the germination of weed seeds, preventing them from establishing roots and shoots. This proactive approach makes them a valuable tool in maintaining a weed-free lawn or garden. See our Pre-emergents 101 blog post for more.

How Pre-Emergents Work

Pre-emergent herbicides create a protective barrier on the soil surface, inhibiting the germination of weed seeds. These herbicides are particularly effective against annual grasses and broadleaf weeds. They work by disrupting the early stages of seed development, preventing roots and shoots from forming. This ensures that many weeds never see the light of day, providing long-lasting protection for your turfgrass.

To truly grasp the effectiveness of pre-emergent herbicides, it’s essential to understand the science that drives their action. These herbicides typically consist of active ingredients that interfere with the early stages of seed development in weeds. By disrupting key processes, such as root and shoot formation, pre-emergents create an environment hostile to weed growth.

The timing of pre-emergent application is critical. Ideally, it should be done in advance of the weed germination period, which varies depending on your region and climate. Early spring or fall applications are common, aligning with the periods when weed seeds are most likely to start their journey towards the surface.

When to Apply Pre-Emergent

Knowing when to apply pre-emergent is crucial for its effectiveness. Ideally, apply it in early spring or fall before weed seeds start to germinate. Timing may vary depending on your region and climate, so keep an eye on soil temperature and local conditions.

Timing is everything when it comes to pre-emergent applications on turfgrass. Understanding the life cycle of common weeds in your area is crucial for effective control. In regions with cool-season grasses, such as Kentucky bluegrass or fescue, fall applications are ideal, targeting winter annuals like chickweed and henbit.

When it comes to pre-emergent herbicides for warm-season grasses like bermudagrass or zoysiagrass, spring applications before the growing season are recommended. This helps prevent the emergence of warm-season annual weeds like crabgrass. In both cases, monitoring soil temperatures can provide valuable insights into the optimal timing for pre-emergent application.

Types of Pre-Emergent Herbicides for Turfgrass: What Types of Pre-Emergent Exist?

While pre-emergents will all do the same thing, let’s clarify the variations in terminology and type that you’ll encounter when researching pre-emergent herbicides:

Preemergence Herbicides

The term preemergence herbicide is a synonym for pre-emergent herbicide (it is sometimes also spelled as preemergent). Regardless of the syntax choice, they are all herbicides applied before weed emergence, targeting the seeds and seedlings in the soil.

Weed Preventer

Another synonym for pre-emergent herbicides, emphasizing their preventive nature.

Selecting the right type of pre-emergent herbicide is paramount for success. Turf managers and homeowners can choose from various formulations, each with its unique characteristics:

Granular Pre-Emergent Herbicides

A type of pre-emergent herbicide that comes in granule form, making it easy to spread evenly across turfgrass. Granular formulations are solid particles that can be spread across the turf and sink into the ground, absorbed by the soil and dispersed. Granular herbicides will often need to be watered in to be effective. They are convenient to use, providing a consistent barrier when applied with a spreader. Granules are particularly effective in preventing the germination of grassy weeds like crabgrass.

Liquid Pre-Emergent Herbicides

A formulation that comes in liquid form, suitable for thorough coverage and quick absorption into the soil. The advantages of liquid pre-emergents include thorough coverage and quick absorption into the soil. They are suitable for large areas and can be applied using a sprayer. Liquid pre-emergents are versatile and can target a broad spectrum of weed types.

Spray Pre-Emergent Herbicides

Spray formulations are a subset of liquid pre-emergents, often applied as a fine mist using specialized equipment. They are suitable for precision targeting and are commonly used in professional turf management settings.

Each formulation has its advantages, and the choice depends on factors such as the size of the turf area, the specific weeds you’re targeting, and your preferred application method.

Best Practices for Applying Pre-Emergent Herbicides on Turfgrass

Achieving optimal results with pre-emergent herbicides requires attention to detail and adherence to best practices. Here are some key considerations for applying pre-emergents on turfgrass:

  1. Proper Calibration of Equipment:

Whether you’re using a spreader for granular formulations or a sprayer for liquid ones, ensuring proper calibration is crucial. This ensures an even application and prevents under or over-application, optimizing the efficacy of the pre-emergent barrier.

  1. Uniform Coverage:

Consistency is key when applying pre-emergents. Ensure uniform coverage across the entire turf area to create a continuous barrier against weed germination. Overlapping application patterns can help achieve this consistency.

  1. Follow Label Instructions:

Always follow the instructions provided on the product label. This includes information on the recommended application rates, timing, and safety precautions. Deviating from the label guidelines can lead to suboptimal results or potential harm to the turfgrass.

  1. Consider Soil Conditions:

The effectiveness of pre-emergent herbicides can be influenced by soil conditions. Adequate soil moisture is essential for activation, so be mindful of irrigation schedules. Applying pre-emergents to dry soil may result in reduced efficacy.

Pre-Emergent Applications in Landscape Beds

As you gear up for pre-emergent applications in your landscape beds this spring, there are a few key considerations to bear in mind. The products you choose will hinge on the specific weeds you’re targeting, the ornamentals gracing your landscape beds, and, of course, your budget constraints.

A granular product like BroadStar will give up to five months of solid control, making it a go-to for savvy lawn care operators. On the liquid front, Flumishield takes charge of unwanted grass and broadleaf weeds. When you’re applying liquid in your landscape beds, a touch of dye is a wise move to ensure thorough coverage. It is also available in granular form.

Whichever you choose, keep in mind that summer weeds tend to be trickier than their spring counterparts, so a second application later in the season might be in order.

Pre-Emergent Late Application

Is it too late to use pre-emergent herbicide? That’s one of the commonly asked questions about pre-emergent herbicides (link to our commonly asked questions blog for more). The answer will depend on your location and climate. In areas with prolonged warm seasons, late spring applications may still be effective. However, it’s generally recommended to apply pre-emergent earlier for optimal results. Get a more in-depth scoop on if it’s not too late to apply pre-emergents in our late application blog.

Effectiveness of Pre-Emergents on Specific Weeds

Different pre-emergent herbicides target specific weed species. For instance, Dimension is known for its effectiveness against crabgrass, while Oxadiazon is an all-rounder. Always check product labels for information on targeted weeds to make sure you’re getting the product you need.

Common Varieties of Pre-Emergent Herbicides and Their Effectiveness

The market offers a plethora of pre-emergent herbicides, each with its unique blend of active ingredients. Here are some common varieties and their effectiveness on specific weeds:

Common Pre-Emergent Herbicides

Active Ingredient Trade Name Target Weeds
Indaziflam Specticle Grassy weeds/Broadleaf weeds
Dithiopyr Dimension Grassy weeds/some Broadleaf weeds
Oxadiazon Ronstar Grassy weeds/Broadleaf weeds
Pendimethalin Pendulum Grassy weeds/Broadleaf weeds
Dimethenamid/Pendimethalin  Freehand Grassy weeds/Broadleaf weeds
Isoxaben/Dithiopyr Crew Grassy weeds/Broadleaf weeds
Prodiamine Kade Grassy weeds/Broadleaf weeds
Izoxaben Gallery Grassy weeds/Broadleaf weeds

Some of the most popular options include:

  1. Kade (Prodiamine):

Known for its effectiveness against crabgrass, Kade offers long-lasting control and is versatile in targeting a range of grassy and broadleaf weeds.

  1. Dimension (Dithiopyr):

Effective against both grassy and broadleaf weeds, Dimension is known for its extended control period. It’s particularly useful in preventing crabgrass and foxtail infestations.

  1. Pendulum (Pendimethalin):

Pendulum is renowned for its broad-spectrum control, targeting a variety of grassy and broadleaf weeds. It’s a reliable choice for preventing the emergence of annual grasses and certain broadleaf weeds.

What You Need to Know About Pre-Emergent Breakthrough

When we talk about pre-emergent herbicides, breakthrough is the term that is used when weeds decide to show up despite the use of a pre-emergent herbicide. The chemical barrier these herbicides are supposed to create near the soil’s surface sometimes struggles to form properly due to certain environmental conditions. Other times, the environment itself messes with the barrier or gives weeds a sneaky way around it.

As we mentioned earlier, watering in pre-emergent herbicides is a big deal because they need water to set up that chemical barricade in the soil. When it’s dry, the chemistry has a hard time spreading into the soil—and even after the chemical barrier has done its job, it’s crucial to keep the soil moist. If the soil gets dry and the ground starts cracking, that presents an opportunity for weeds to break through.

On the other side of the coin, if excessive irrigation and/or rainfall take place, those pre-emergent chemicals could get washed away. Keep an eye on the weather and tweak your irrigation schedule accordingly.

Pre-Emergent Safety

While most pre-emergent herbicides are safe for pets and humans once they are applied and dry, it’s essential to follow product instructions carefully. Always consult the product label and safety data sheet (SDS) before use. While pre-emergent herbicides are generally safe when applied correctly, it’s essential to consider safety concerns, especially when pets and humans frequent the treated areas.

Pre-Emergent Safety for Pets and Children

Most pre-emergent herbicides are safe for pets and humans once they are applied and dry. However, it’s crucial to follow product instructions carefully. Keep pets and children away from treated areas until the product has dried completely.

Read Labels and SDS

Always consult the product label and safety data sheet (SDS) before use. These documents provide essential information on safety precautions, first aid measures, and proper handling of the product.

Mastering the use of pre-emergent herbicides is a game-changer in the battle against weeds. By understanding the best pre-emergent for your lawn, ideal application timing, and the specific needs of your region, you can promote lush, weed-free turfgrass. Whether you opt for granular or liquid formulations, with the right pre-emergent strategy, your turf is set to thrive.

Remember, well-maintained turf starts with prevention. Make pre-emergent herbicides your first line of defense against invasive weeds.