In the battle against unwanted weeds, post-emergent herbicides are invaluable tools that effectively tackle plants that have already sprouted. But with so many types of post-emergent herbicides at your disposal, how do you make the right choice?
Our guide takes a closer look at each type so you can decide which one will be most effective against the weeds in your yard.
What are post-emergent herbicides?
Post-emergent herbicides control weeds that have already germinated and emerged from the soil. Unlike pre-emergent herbicides, which stop 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.
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 of systemic post-emergent herbicides
✓ Broad-spectrum control targets a wide range of weeds.
✓ Can be applied at various stages of weed growth.
✓ Provide rapid action, which is beneficial for controlling weeds quickly and efficiently.
✓ Available in different forms, including liquids, granules, and ready-to-use types.
Cons of systemic post-emergent herbicides
✗ Liquid formulas 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.
✗ May not provide complete control for certain resistant weed species, so you may have to up your weed management game. Think proper plant spacing, mowing, tilling, mulching, introducing natural weed enemies such as insects or diseases into your yard, implementing preventative measures, and regularly monitoring your lawn and garden.
✗ Some types can last long after application, 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.
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 (movement from the point of absorption to other parts of 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 of contact post-emergent herbicides
✓ 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.
✓ Typically applied directly to the foliage of target weeds.
Cons of contact post-emergent herbicides
✗ Herbicide may not reach all parts of the weed.
✗ Inadequate coverage can lead to uneven control and allow some weeds to persist.
✗ 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, which can increase the cost and labor involved.
✗ Weeds with sturdy cuticles or hairy surfaces are harder to kill with a contact herbicide approach.
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 of granular post-emergent herbicides
✓ Easy to handle and apply using spreaders, making them convenient for both small and large properties.
✓ 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 last longer, providing extended control and reducing the need for frequent reapplication.
✓ Generally stable and easy to store, with a longer shelf life than some liquids.
Cons of granular post-emergent herbicides
✗ You must apply water after application, otherwise, the treatment is ineffective.
✗ If the spreader isn’t calibrated correctly, achieving an even distribution of granules can be challenging. There is also the risk of overapplication, resulting in damage or death of desirable plants and turfgrasses.
✗ May not act as quickly as some liquid formulas.
✗ There is the risk of runoff into nearby bodies of water.
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 properties.
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 of liquid post-emergent herbicides
✓ They’re often fast-acting, providing relatively quick results.
✓ They come in various formulas, making them versatile for targeting different types of weeds.
✓ Some types can be mixed with other herbicides or additives, allowing for a customized approach to weed control.
Cons of liquid post-emergent herbicides
✗ 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.
✗ There’s a risk of overapplication, which may result in damaged plants or grass.
✗ May pose more risks for skin and eye exposure.
✗ They have specific storage requirements, and their shelf life might be shorter than some granular herbicides.
✗ Overapplication can cause staining on surfaces such as concrete or natural stone.
✗ 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 sedges.
Pros of selective post-emergent herbicides
✓ Often more convenient than removing weeds manually. The application includes liquid or granular options, making the process efficient and less labor-intensive.
✓ Offer a variety of products that target weeds present in your lawn.
✓ Suitable for smaller areas or yards.
Cons of selective post-emergent herbicides
✗ Since they’re weed-specific, they lack broad-spectrum control. You might need multiple herbicides if you have more than one type of weed.
✗ Some types are more effective on mature or established weeds and may not be as potent against newly germinated weeds.
✗ May require more than one application.
✗ Usually more expensive 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 of non-selective post-emergent herbicides
✓ Can kill a broad range of plants, which is beneficial if you’re dealing with multiple weed types at the same time, in the same space. You won’t have to be as precise in your application or purchase different herbicides to target the weeds in your yard.
Cons of non-selective post-emergent herbicides
✗ There’s 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 remain in the soil, affecting soil microbial activity. ✗ This persistence can lead to long-term impacts on the ecosystem.
Post-emergent herbicide ingredients
Post-emergent herbicides come in various forms 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 (Selective, systemic herbicide) – Works best on grassy weeds like crabgrass, witchgrass, barnyard grass, and foxtail weeds but struggles to kill broadleaf weeds. Can be liquid or granular.
- Dicamba (Selective, systemic herbicide) – Works best on broadleaf weeds like dandelion, clover, spurge, thistle, and knotweed. Can be liquid, granular, or powder.
- Glyphosate (Non-selective, systemic herbicide) – Works best on every type of plant and can kill grassy weeds like crabgrass, broadleaf weeds like dandelion or thistle, and turfgrass like bluegrass. Can be liquid or granular.
- Glufosinate (Non-selective, contact herbicide) – 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. Can be liquid or granular.
- Methanearsonate (Selective, contact herbicide) – Works best on crabgrass and nutsedge. Can be liquid or granular.
- Bentazone (Selective, contact herbicide) – Works best on yellow nutsedge, annual nutsedge, and perennial kyllinga. Comes as a liquid.
- Triclopyr (Selective, systemic herbicide) Works best on dandelion, thistle, clover, chickweed, chicory, poison ivy, and woody weeds. Can be liquid, granular, or powder.
Which post-emergent herbicide is right for you?
With so many different post-emergent herbicides 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.
- What kind of weeds do you have? Determine the types of weeds you need to eliminate. Different herbicides are effective against different weed species, so knowing your target weeds is crucial for long-term success.
- Where are your weeds growing? Consider the location where you’ll be applying the herbicide. It may be a lawn, garden, or agricultural field. Herbicides are formulated to target different environments, which is why not every type may work for you. When choosing herbicide, consider soil composition, weed growth habits, and the surrounding ecosystem. If unsure, ask a professional for guidance.
- How do you want to target your weeds? It’s crucial to know how weed killers work. Some interfere with certain enzymes or damage plant cell walls, while others block photosynthesis (the way in which plants use carbon dioxide, sunlight, and water to make their food). Understanding these details can help you target the weed correctly and prevent weed resistance.
- How long do you want the herbicide to last? Consider how long the herbicide stays in the soil. Some herbicides break down quickly, providing short-term control; others have longer residual activity that may affect future plantings. It all depends on your immediate needs and future plans in terms of landscaping and soil health.
- Do you want an herbicide that’s eco-friendly? Evaluate the environmental impact of the herbicide. Ensure it has low toxicity levels, reduced runoff potential, and minimal impact on water quality. It should break down quickly without damaging surrounding non-target plants or organisms and come in recyclable or biodegradable packaging. Another tip? Look for recognized certifications on the packaging, indicating compliance with organic standards.
- How do you want to apply it? Some herbicides come in liquid form for spray applications, while others may be granular or concentrated. Choose one that aligns with your preferred application method and available equipment.
- How much do you want to spend? Although cost is essential when choosing herbicide, it should be balanced with environmental impact, effectiveness, and long-term benefits.
- 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 show 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.
Are there organic post-emergent herbicides?
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.
What’s the difference between concentrated and ready-to-use formulas?
The main difference lies in the application. As the name suggests, concentrated formulas 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.
Looking for professional help?
While tending to your yard can be oddly satisfying and a chance to unleash your inner green thumb, not everyone’s equipped to do it on their own. After all, you have to select the right herbicide, apply it correctly, and deal with any environmental repercussions from incorrect handling.
So, why not reach out to a local pro for comprehensive and tailored weed management services that can make your life easier? They can assess your individual needs, suggest a herbicide that works, and implement the right strategy for success.
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