Types of Post-Emergent Herbicides

Post-emergent herbicides are your allies in the fight against pesky weeds. They swoop in after weeds have made an appearance and stake their claim, removing unwanted visitors in your yard. 

This detailed guide outlines everything you need to know about the types of post-emergent herbicides at your disposal. We unpack what they are and give you a rundown of every advantage and disadvantage you should be aware of.

What Are Post-Emergent Herbicides?

Post-emergent herbicides control weeds that have already germinated and emerged from the soil. Unlike pre-emergent herbicides, which target weed seeds before they sprout, post-emergent herbicides are applied to actively growing weeds. Many homeowners use them to manage existing weed infestations in lawns, gardens, agricultural fields, and other landscapes.

Post-emergent herbicides come in various formulations with one or multiple ingredients. Each ingredient can kill a specific type of weed, and knowing what weeds you have can help narrow down which one will work best on your lawn.

• Fluazifop – Works best on grassy weeds like crabgrass, witchgrass, barnyard grass, and foxtail weeds. It struggles to kill broadleaf weeds. 
• Dicamba – Works best on broadleaf weeds like dandelion, clover, spurge, thistle, and knotweed.
• Glyphosate – Works best on every type of plant and can kill grassy weeds like crabgrass, broadleaf weeds like dandelions or thistle, and turfgrass like bluegrass.
• Glufosinate – Works best on yellow nutsedge, creeping bentgrass, foxtail, garden spurge, ground ivy, and carpet weeds. This is a good option if you have weeds that have developed a tolerance to Glyphosate.
• Methanearsonate – Works best on crabgrass and nutsedge.
• Bentazone – Works best on yellow nutsedge, annual nutsedge, and perennial kyllinga.

Types of Post-Emergent Herbicides

Some of the most common post-emergent herbicides you may find at your local garden center include:

Systemic Post-Emergent Herbicides

You may have to practice patience with systemic post-emergents, as they take longer to provide the desired results. This variety is absorbed by the plant and translocated throughout its vascular system, affecting various parts of the plant, including the roots and shoots. The good news? With the root system out of the way, you won’t have to worry about the weeds sprouting back up again.

Pros

• Broad-spectrum control targets a wide range of weeds.
• Can be applied at various stages of weed growth, providing flexibility in application and adaptability to different weed challenges.
• Provide rapid action, which is beneficial for controlling weeds quickly and efficiently.
• Available in different formulations, including liquids, granules, and ready-to-use types. This makes them easy to apply and reduces the need to invest in new application equipment. You can use what you have.

Cons

• Liquid formulations can be susceptible to drift, where the herbicide particles move with the wind during application, damaging neighboring crops, vegetation, or sensitive areas.
• Can leach into the soil and contaminate existing groundwater. This has environmental implications in areas with vulnerable ecosystems or water sources.
• May not provide complete control for certain resistant weed species, so you may have to turn to integrated weed management strategies for better results. This involves combining multiple weed control methods to maximize effectiveness and minimize environmental impact. Think proper spacing, mowing, tilling, mulching with grass clippings, introducing natural weed enemies such as insects or diseases that target specific weeds, implementing preventative measures, and regularly monitoring your lawn and garden.
• Some types can persist in the environment, affecting non-target plants in future growing seasons. 
• Exposure to certain systemic herbicides may pose health risks, including skin and eye irritation, respiratory issues, or more severe health problems. 
• May be relatively expensive, particularly for large-scale agricultural operations. The additional cost may be an influencing factor in choosing this type.

Contact Post-Emergent Herbicides

If you’re on the hunt for a fast-acting herbicide that acts primarily on the plant parts it comes into direct contact with, contact post-emergent is your best bet. Unlike systemic herbicides, which are absorbed and translocated within the plant, contact herbicides affect only the areas where they are applied. They’re valuable for their quick action and effectiveness when rapid vegetation control is necessary.  

Pros

• While some contact herbicides are selective, others have a broader spectrum, effectively controlling a wide range of weed species. 
• Tend to have minimal or no residual effects in the soil, meaning that the active ingredients break down relatively quickly, reducing the risk of long-term impact on soil health or the development of weed resistance.
• Can be used in combination with other herbicides, including systemic herbicides, to enhance overall weed control and provide more sustainable results.
• Typically applied directly to the foliage of target weeds, making them convenient to use.

Cons

• Their limited translocation ability means that the herbicide may not reach all parts of the weed plant.
• Inadequate coverage can lead to uneven control and allow some weeds to persist.
• Although less persistent in the soil, their use can still have environmental implications. Runoff may contaminate bodies of water and affect marine ecosystems.
• Accidental drift or overspray may still cause unintentional damage to nearby non-target plants.
• May require more frequent applications compared to systemic herbicides, especially with fast-growing or perennial weeds. This can increase the cost and labor associated with your weed control strategy.
• Weeds with sturdy cuticles or hairy surfaces are usually less susceptible to the contact herbicide approach. Plus, overreliance on a single mode of action can lead to weed resistance. Always opt for rotation and diversification to see optimal results.

Granular Post-Emergent Herbicides

As the name suggests, granular post-emergent herbicides are applied in solid granular form. The granules are often coated or filled with the herbicide. Once applied to the soil surface, they require activation through irrigation or rainfall to break down and release the active ingredients.

Pros

• Easy to handle and apply using spreaders, making them convenient for both small and large-scale applications. 
• Unlike liquid weed killers that can blow away with the wind, these granules stay put better. So, there’s less chance of them accidentally landing on plants you want to keep. 
• Some granular post-emergents have longer residual activity, providing extended control and reducing the need for frequent reapplication.
• Generally stable and easy to store, with a longer shelf life than some liquid alternatives.

Cons

• If there’s no rainfall or irrigation, the effectiveness of the treatment may be compromised.
• If the spreader isn’t calibrated correctly, achieving an even distribution of granules can be challenging. Overapplication is also risky, resulting in damage or death of desirable plants, lawn turfgrasses, or other vegetation in the treated area.
• May not act as quickly as some liquid formulations, which can be a limitation in situations requiring rapid weed control.
• Runoff may carry the active ingredients into nearby bodies of water, increasing environmental risks.

Liquid Post-Emergent Herbicides

These weed killers in liquid form are another useful way to target existing weeds in your lawn, garden, or field. They offer versatility in application, which typically includes handheld sprayers for spot treatments, backpack sprayers for smaller areas, and aerial or tractor-mounted sprayers for larger fields. 

You put the liquid herbicide into your sprayer of choice and spray it directly onto the leaves of the weeds you want to get rid of. It’s important to follow the instructions on the bottle, wear any recommended protective gear, and be careful not to get the liquid on plants you want to keep.

Pros

• They’re often fast-acting, providing relatively quick results in terms of weed control.
• They come in various formulations, making them versatile for targeting different types of weeds, whether broadleaf weeds, grasses, or a combination of both.
• Some types can be mixed with other herbicides or additives, allowing for a customized approach to controlling weeds.

Cons

• The liquid particles are susceptible to drift, carried by wind to unintended areas, and potentially causing harm to non-target plants.
• Proper application often requires specialized equipment like sprayers, which you may not have access to.
• Due to the liquid form, there’s a risk of overapplication, which may result in damaged plants or grass.
• May pose more risks for skin and eye exposure, which is why following safety precautions and wearing protective gear is crucial during handling.
• They have specific storage requirements, and their shelf life might be shorter than some granular herbicides.
• Overapplication generally causes stains or residues on treated surfaces, impacting visual appearance. Porous surfaces such as concrete or natural stone may be more prone to staining than metal or glass.
• Runoff can carry the active ingredients into nearby water sources, damaging aquatic ecosystems.

Selective Post-Emergent Herbicides

Selective herbicides work only on the weed — or weeds — they’re designed to kill. If you mistakenly spray or spill a selective post-emergent on grass or plants, it won’t kill them. With this type of herbicide, you can kill broadleaf weeds, grassy weeds, and different sedge types.

Pros

• Often more convenient than removing weeds manually. The application includes liquid or granular options, making the process efficient and less labor-intensive.
• Offer choice diversity, allowing you to choose a product that targets the weeds present in your lawn.
• Suitable for smaller areas or yards.

Cons

• Since they’re weed-specific, they lack broad-spectrum control. You might need multiple herbicides if you have a diverse range of weed species.
• Some types are more effective on mature or established weeds and may not be as potent against very young or newly germinated weeds.
• May require more than one application for desired effectiveness.
• Usually have a higher price point than non-selective treatments.

Non-Selective Post-Emergent Herbicides

A non-selective post-emergent herbicide will kill everything in its path, including flowers, bushes, and grass. These indiscriminate herbicides control weeds around fences, in driveway and sidewalk cracks, or across large areas.  

If you’re unsure what kind of weeds you’re dealing with and don’t want to do some basic research online to identify your weedy foes, applying a non-selective herbicide should help.

Pros

• Since non-selective herbicides target a broad range of plants, precise application is less needed. This can make them easier to use for certain applications.

Cons

• A higher risk of non-target damage. These herbicides can harm or kill desirable plants, including flowers, shrubs, and trees, if not applied carefully.
• Can have a more significant impact on the environment than selective herbicides. They affect many different plant species, resulting in the loss of vegetation diversity. This, in turn, may impact various organisms’ habitats and food sources.
• May have adverse effects on soil health. Some non-selective herbicides can persist in the soil, affecting soil microbial activity. This persistence can lead to long-term impacts on the ecosystem.

Which Post-Emergent Herbicide Is Right for You?

With so many different post-emergent herbicide options to choose from, it can take time to find the right one for your lawn. Considering these factors can help you save time and money and kill only the invasive plants on your property. 

• Target weeds – Determine the types of weeds you need to eliminate. Different herbicides are effective against different weed species, so knowing your target weeds is crucial.
• Application location – Consider the location where you’ll be applying the herbicide. It may be a lawn, garden, or agricultural field. Some herbicides are suitable for specific settings, while others may have restrictions. This information is available on the label.
• Operating method – Another important aspect is understanding how the herbicide works. Some inhibit specific enzymes or disrupt cell membranes, while others inhibit photosynthesis and amino acid synthesis. Knowing these aspects of weed control can help prevent or manage resistance issues.
• Residual activity levels – Consider the persistence of the herbicide in the soil. Some herbicides break down quickly, providing short-term control; others have longer residual activity. The latter may affect future plantings or contribute to environmental concerns.
• Ecological footprint – Evaluate the environmental impact of the herbicide. Ensure it has low toxicity levels, reduced runoff potential, and minimal impact on water quality.
• Application method – Some herbicides come in liquid formulations for spray applications, while others may be granular or concentrate. Choose a formulation that aligns with your preferred application method and available equipment.
• Cost and budget – Although cost is an essential factor when choosing herbicide, it should be balanced with the effectiveness and long-term benefits of the chosen product.
• Compatibility with other lawn care products – Check for compatibility if you’re using other chemicals in your landscaping or lawn care practices. Mixing certain herbicides or pesticides can lead to reduced effectiveness or side effects you probably want to avoid.

FAQ About Post-Emergent Herbicides

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

If you’re wondering when to apply your post-emergent, consider these key aspects before starting:

• The weed growth stage – Post-emergents are best applied when the target weeds are in the early stages of growth or actively growing, as this is when they’re most vulnerable.
• The weather – Choose a calm day with little to no wind to prevent herbicide drift. Rainfall immediately after application may wash away the herbicide, reducing its effectiveness. Avoid application during extremely hot or dry conditions.
• Temperature – Herbicides are often more effective when temperatures are within a certain range. Consult the product label for specific temperature recommendations, as extreme heat or cold can significantly reduce their effectiveness.
• Time of day – Early morning or late afternoon is often preferable for herbicide application. Temperatures are generally milder, and there’s a reduced risk of stress on your plants.
• Soil moisture – Adequate soil moisture boosts herbicide absorptions. If soil moisture is too low, consider postponing the application until conditions improve.

How Long Does It Take for Post-Emergent Herbicide to Provide Results?

The time it takes for your post-emergent herbicide to work depends on the herbicide itself, the target weed’s growth stage, and the weather conditions. Some herbicides provide quick, visible results within days, while others may take weeks to act.

Is Post-Emergent Herbicide Available in Organic Formulas?

Some organic-approved post-emergent herbicides are available, usually based on natural ingredients. Check product labels to ensure they meet organic certification standards. Discuss it with a professional if unsure.

You can also consider making homemade weed killer if environmental concerns are an issue.

What’s the Difference Between Concentrated and Ready-to-Use Formulas?

The main difference lies in the application. As the name suggests, concentrated formulations require dilution with water, as they contain a higher concentration of the active ingredient(s). The good part is that this option is cost-effective and allows you to adjust the concentration level based on your individual needs. Before starting, read the manufacturer’s instructions carefully.

Ready-to-use products come pre-diluted and mixed. As a result, they’re more convenient and user-friendly, eliminating the need to do your own mixing. If you prefer simplicity, this is a good choice for you. Plus, they’re great for smaller yards and spot treatments without additional equipment. You can simply use the spray nozzle or applicator they usually come with.

Professional Assistance Right Around the Corner

The intricacies of selecting the right herbicide, applying it correctly, and dealing with any environmental repercussions from incorrect handling aren’t for everyone. If you’re one of those people, we’ve got just the thing.

Reach out to a local pro for comprehensive and tailored weed management services that can make your life easier. Let them assess your individual needs, recommend the right herbicide for your yard, and ensure your fight against weeds is a success.

Main Image Credit: hdmddphoto / Canva Pro / License