Post-emergent herbicides are crucial in managing weed infestations and maintaining the health and aesthetics of landscapes, lawns, and agricultural areas. Unlike pre-emergent herbicides, which target weed seeds before they germinate, post-emergent herbicides are designed to control weeds that have already sprouted and are actively growing. Our buyer's guide aims to provide you with essential information to make informed decisions when selecting and using post-emergent herbicides.
What Are Post-Emergent Herbicides?
Post-emergent herbicides are chemical compounds formulated to target and eliminate unwanted plants after they have already emerged from the soil. These herbicides are usually applied directly to the leaves and stems of target weeds, where they are absorbed and transported to the plant's vital parts, like the roots. They disrupt critical biological processes and eventually cause plant death. The selective nature of post-emergent herbicides allows them to minimize harm to desirable plants when used correctly.
Common Scenarios for Using Post-emergent Herbicides
Post-emergent herbicides are used in various scenarios to address weed challenges:
Lawns often face weed invasions that can compromise their health and appearance. Post-emergent herbicides can effectively target and control broadleaf and grassy weeds, ensuring a lush and weed-free lawn.
In agricultural settings, post-emergent herbicides manage weed competition in crops, safeguarding their yield potential and reducing competition for essential resources.
Post-emergent herbicides help manage weeds in areas such as driveways, sidewalks, and patios. By effectively eliminating unwanted plants, these herbicides contribute to a clean and well-maintained appearance.
In each scenario, selecting and applying the right post-emergent herbicide is key to achieving desired results while minimizing negative impacts to the environment and non-target plants.
Factors to Consider Before Purchasing Post-Emergent Weedkiller
Before purchasing a post-emergent herbicide, assessing several key factors is important to ensure you choose the right product for your weed problem. Here are the critical considerations to keep in mind:
Weed Types and Targets
Different post-emergent herbicides are formulated to target specific types of weeds. So you’ll need to identify the weeds causing problems in your yard. Weeds can generally be categorized into three main groups:
- Broadleaf weeds: These weeds have broad, flat leaves and include plants like dandelions, clover, and chickweed.
- Grassy weeds: Grasses are thin-leaved plants that often resemble desirable turf grasses. Examples include crabgrass, foxtail, and quackgrass.
- Sedge and aquatic weeds: Sedges are grass-like plants that thrive in wet areas, while aquatic weeds grow in or near water bodies. Examples include nutsedge and various pond weeds.
Each type of weed requires a specific herbicide formulation for effective control, so understanding the weeds you're dealing with will guide your product selection.
Related reading: What Types of Weeds Look Like Grass?
Post-emergent herbicides can be either selective or non-selective:
- Selective herbicides: These target specific types of weeds without harming desirable plants. They are commonly used in lawns and other areas where you want to preserve the existing vegetation.
- Non-selective herbicides: These herbicides can kill a wide range of plant types, including both weeds and desirable plants. They are useful for clearing areas before planting or managing weeds in non-crop spaces.
The environmental impact of a post-emergent herbicide involves its effects on non-target plants, the persistence of the chemical in soil and water, and its potential effects on beneficial insects and wildlife:
- Non-target plants: Selective herbicides should be chosen when you need to protect nearby plants. Non-selective herbicides can have unintended consequences if not used carefully.
- Persistence: Some herbicides remain active in the soil for an extended period. This can impact future plant growth and potentially leach into water sources.
- Wildlife and beneficial insects: Consider the potential effects on pollinators, beneficial insects, and other wildlife in the application area.
Types of Post-emergent Herbicides
Post-emergent herbicides can be categorized into different types based on their modes of action and how they affect target plants. Understanding these types will help you choose the right herbicide for your specific weed control needs:
As the name suggests, contact herbicides work upon direct contact with the plant's foliage. They are absorbed by the leaves and stems but do not translocate extensively to other parts of the plant. These herbicides provide quick, visible results but may not completely eliminate the weed's root system. They are often used for annual weeds or spot treatments.
- Rapid action and visible results.
- Effective for controlling above-ground parts of weeds.
- Limited root control, which may result in regrowth.
- Repeated applications may be necessary for complete control.
Systemic herbicides are absorbed by the plant and translocated throughout its vascular system, including the roots. This makes them effective against both the visible parts of the plant and the underground root systems. Systemic herbicides are particularly useful for perennial weeds and can provide longer-lasting control.
- Effective against the entire plant, including roots.
- Greater chance of preventing regrowth.
- Translocation can take time, so results are typically not immediate (1-3 weeks).
- Care must be taken to avoid damaging desirable plants through spray drift or root absorption.
Residual herbicides remain active in the soil for a certain period after application. They provide ongoing control by preventing weed seeds from germinating or newly emerging weeds from establishing themselves. Residual herbicides are commonly used in situations where long-term weed prevention is necessary, such as agricultural fields and areas with a history of persistent weed problems.
- Prolonged control, reducing the need for frequent applications.
- Preventive action against future weed growth.
- Potential impact on desirable plants that may be introduced after application.
- Proper application timing is crucial to maximize effectiveness.
Choosing the right type of post-emergent herbicide depends on the kind of weeds you're dealing with, the extent of the infestation, and your desired level of control. Some situations warrant a combination of different types of herbicides for optimal results. Always follow label instructions and guidelines to ensure safe and effective use of these herbicides.
Related reading: How to Kill Weeds Without Killing Your Grass
The effectiveness of a post-emergent herbicide greatly depends on how it's applied. Different application methods are suitable for various scenarios, and understanding these methods will help you achieve the best results while minimizing risks to non-target plants and the environment:
Ready-to-use vs. concentrated formulations: Ready-to-use sprays come pre-mixed and are convenient for small areas or spot treatments. Concentrated formulations require dilution according to the manufacturer's instructions and are better suited for larger areas.
Equipment: Select the appropriate sprayer for your needs, such as hand-held sprayers, backpack sprayers, or larger equipment for extensive areas. Make sure the sprayer is clean and properly calibrated before use.
Application tips: Apply the herbicide evenly, ensuring good coverage of the target weeds while avoiding excessive runoff. Avoid spraying during windy conditions to prevent drift onto non-target plants.
Suitable for larger areas: Granular formulations are ideal for treating larger areas like lawns. They can be applied using a broadcast spreader, ensuring even coverage.
Proper spreading techniques: Calibrate the spreader to the recommended settings and walk steadily to prevent over-application or gaps in coverage.
Precision application: Spot treatments are effective for small infestations or when protecting desirable plants nearby. Apply the herbicide directly to the leaves of the target weed.
Minimizing impact: Be cautious not to allow the herbicide to come into contact with desirable plants. Shielding nearby plants with a piece of cardboard or plastic can help prevent accidental exposure.
Proper application is crucial in achieving the desired results without harming non-target plants or the environment. Always read and follow the manufacturer's instructions on the product label for the best application practices. Additionally, consider weather conditions, such as avoiding application during rain or when rain is expected within 4 hours of treatment. This is to ensure the herbicide's effectiveness.
Related reading: What is the best weed killer spray for lawns?
Safety Precautions and Usage Guidelines
When working with post-emergent herbicides, safety should be a top priority to protect yourself, others, and the environment. Following the label’s usage guidelines and taking necessary precautions will ensure effective weed control while minimizing risks:
Clothing: Wear long sleeves, long pants, and closed-toe shoes to minimize skin exposure to the herbicide.
Gloves: Use chemical-resistant gloves to prevent direct contact with the herbicide. We recommend 14 mil or thicker gloves.
Eye and face protection: Wear safety goggles or a face shield to protect your eyes from accidental splashes.
Wind conditions: Avoid applying herbicides on windy days to prevent drift onto non-target plants, neighboring areas, or people.
Rainfall after application: If rain is expected shortly after application, the herbicide may be washed away or diluted, reducing its effectiveness.
Mixing and Dilution
Proper ratio adherence: When using concentrated formulations, accurately measure and mix the herbicide according to the label instructions. Over or under-dilution can impact the effectiveness. We’ve found that most post-emergent herbicides specify a water dilution rate of 1 gallon per 1000 square feet.
Compatibility with other chemicals: Some herbicides may not mix well with other products. Always read the label for compatibility information. Before mixing large quantities of different products, perform a jar test to confirm compatibility.
Storage and Disposal
Secure storage: Keep herbicides in their original containers and store them out of reach of children and pets, preferably in a locked cabinet.
Proper disposal: Follow local regulations for disposing of unused herbicides and empty containers. Do not pour leftover herbicide down drains or throw containers in the regular trash.
Related reading: How to Get Rid of Weeds — Everything You Need to Know
Our Top Post-emergent Herbicide Products
When selecting a post-emergent herbicide, considering the available products is crucial. Here are a few of what we think are the best post-emergent herbicides that work effectively to eliminate weeds.
Warm-Season Turf Post-emergent Herbicides
Features: Fast-acting systemic selective herbicide designed for broadleaf weed control in lawns.
Active ingredients: Dicamba (57.4%), Iodosulfuron-methyl-sodium (1.9%), Thiencarbazone-methyl (8.7%).
Targeted weeds: Effective against over 150 different types of lawn weeds, including dandelions, dollarweed, crabgrass, and other common broadleaf weeds.
Application instructions: This can be used on all warm-season grasses except Bahiagrass. This professional formulation should be applied from a battery-powered 4-gallon sprayer with a TeeJet foliar spray tip. This herbicide is not to be used via a hose-end sprayer.
Features: A selective herbicide formulated for both grassy and broadleaf control in warm-season turf. Certainty controls weeds such as Poa annua, dandelions, nutsedge, and much more. It can be safely applied to Bermuda grass, Bahia grass, Buffalo grass, Centipede, St. Augustine, Seashore Paspalum, Kikuyu grass, and Zoysia lawns.
Active ingredients: Sulfosulfuron (75%).
Targeted weeds: Sedges and grassy weeds, including yellow and purple nutsedge, bentgrass, chickweed, dandelions, Poa annua, ryegrass, and many more.
Application instructions: This is a professional formulation and should be applied with a battery-powered 4-gallon sprayer with a TeeJet foliar spray tip. This herbicide is not to be applied via a hose-end sprayer. We don’t recommend application if temperatures are over 100F. If temps are that high, apply in the evening when they dip below 100F and elect to spot spray instead of blanket spraying.
Cool-Season Turf Post-Emergent Herbicides
Features: Tenacity herbicide is an excellent broadleaf and grassy weed killer for cool-season turf. It can be used for pre-and post-emergence control of more than 46 broadleaf weed and grass species. It is great for cool-season grasses like Fescue, Rye, and Kentucky Bluegrass without fear of damaging turf.
Active ingredients: Mesotrione (40%).
Targeted weeds: Controls 46 varieties of grassy and broadleaf weeds, making it suitable for lawns with mixed weed types.
Application instructions: This is a professional formulation and should be applied with a battery-powered 4-gallon sprayer with a TeeJet foliar spray tip. This herbicide is not to be applied via a hose-end sprayer. DO NOT apply this product on Bentgrass, Kikuyugrass, Zoysiagrass, Seashore Paspalum, or Bermudagrass. It will damage or kill these grass types. Do not apply if temperatures are over 90F. If temps are that high, apply in the evening when they dip below 90F and elect to spot spray instead of blanket spraying.
Features: SedgeHammer® is a selective herbicide used to kill nutsedge and kyllinga. It is a safe weed killer that won't kill your grass. This product makes an excellent “spike” or addition to Tenacity Herbicide if you have specific problems with sedges.
It can be used on cool-season turf like Kentucky Bluegrass, Turf-type Tall Fescue (all fescues), and Ryegrass. It’s also suitable for some warm-season turfs, such as Bermuda grass, St Augustine, Zoysia grass, Centipede, and Bahiagrass.
Active ingredients: Halosulfuron-methyl (75%).
Targeted weeds: Great for treating yellow and purple nutsedge and kyllinga.
Application instructions: As with the previous products on our list, a battery-powered 4-gallon sprayer with a TeeJet foliar spray tip is recommended. It is not to be applied via a hose-end sprayer. For best results, use non-ionic surfactant with Sedgehammer.
Post-emergent Herbicides for Cool and Warm-Season Turf
Features: Triad Select™ Herbicide uses a blend of three herbicides to kill a wide range of broadleaf weeds. This weed killer is safe for grass and is among the best for killing dandelions. Triad Select is an excellent herbicide that's a step up from store-bought options.
It is one of the best weed killers that won't kill grass when used as directed. Triad Select is a safe weed killer for most warm and cool-season lawns.
Active ingredients: 2,4-D (30.89%), MCPA ( 8.23%), Dicamba (2.77%).
Targeted weeds: Many types of broadleaf weeds, including dandelions, ground ivy, knotweed, clover, and spurge.
Application instructions: A battery-powered 4-gallon sprayer with a TeeJet foliar spray tip is recommended. It is not to be applied via a hose-end sprayer. Do not apply if temperatures are over 90F. If temps are that high, apply in the evening when they dip below 90F and elect to spot spray instead of blanket spraying.
Non-selective Organic Post-emergent Herbicide
Features: Mirimichi Green Organic Weed Control spray is a fast-acting, nonselective, organic weed killer for residential, commercial lawns, and non-crop uses. This is an excellent alternative to glyphosate for spot-spraying lawn weeds, sidewalks, and flower beds. This weed killer is non-selective. It will kill your grass as well as weeds.
Active ingredients: Ammonium Nonanoate
Targeted weeds: Several types of broadleaf and grassy weeds, including moss, plantain, Poa annua, bentgrass, crabgrass, and fescue.
Application instructions: Mirimichi Green Organic Grass & Weed Killer comes in a convenient ready-to-use spray bottle — no dilution is necessary. It controls weeds in homeowners gardens, driveways, patios, and flower beds.
Before choosing a specific product, research its compatibility with your intended application area, target weeds, and follow the manufacturer's guidelines for proper usage. Keep in mind that product availability and formulations may change over time, so it's recommended to check the most recent information before making a purchase decision.
Remember that product effectiveness can vary based on factors such as weed species, application timing, and environmental conditions. Conduct thorough research or contact us if you need help determining which product best suits your needs.
Choosing the Right Post-emergent Herbicide for Your Needs
Selecting the most suitable post-emergent herbicide requires a thoughtful assessment of your unique situation and requirements. Here are the steps to guide you in making an informed decision:
Assessing Your Weed Situation
Identify weed types: Determine the types of weeds you need to target — broadleaf, grassy, or both. This will help you narrow down herbicides designed to control those specific weeds.
Weed density: Evaluate the extent of the weed infestation. Is it a minor problem or a widespread issue requiring more intensive treatment?
Application area: Consider the area you need to treat — lawn, garden, agricultural field, or non-crop space. Most herbicides are formulated for specific environments.
Compatibility with Your Application Area
Lawn type: If you're treating a lawn, ensure the herbicide is safe for your grass type. Some grasses may be more sensitive to certain herbicides.
Agricultural crops: For farms or vegetable gardens, choose herbicides that won't harm your crops. Read labels carefully and research compatibility.
Non-crop areas: In non-crop areas, consider whether you need selective or non-selective herbicides, depending on nearby plants.
Frequently Asked Questions (FAQs)
Navigating the world of post-emergent herbicides can raise a lot of questions. Here are answers to some common queries to provide further clarity:
Q. How often should I apply post-emergent herbicides?
The frequency of application depends on the herbicide used, the weed species, and the stage of weed growth. Follow the manufacturer's recommendations on the product label for application intervals. Repeat applications may be needed for persistent weeds or for ensuring season-long control.
Q. Can post-emergent herbicides harm my desirable plants?
Selective post-emergent herbicides are designed to minimize harm to desirable plants when used as directed. However, there's still a risk of unintended damage. To reduce this risk, apply herbicides during calm weather to prevent drift and shield desirable plants from overspray or accidental contact.
Q. What time of day is best for applying post-emergent herbicides?
Applying herbicides during calm, non-windy conditions is best to prevent drift onto non-target areas. Early morning or late afternoon is often a good choice, as the temperature is cooler, and winds tend to be calmer. Avoid applying herbicides during the heat of the day to prevent herbicide evaporation and potential harm to plants.
Q. How long does it take to see results after applying a post-emergent herbicide?
The speed of results varies based on the herbicide, weed type, and environmental conditions. Contact herbicides can show visible effects within hours, while systemic herbicides take a bit longer, especially if the weed has a well-established root system. We’ve found that most post-emergents produce results within 1- 3 weeks. Patience is key, and following label instructions will give you a better idea of what to expect.
Q. Can I mix different herbicides together for enhanced effectiveness?
Mixing different herbicides can be risky, so we created bundles of post-emergent herbicides that can be used safely on cool-season and warm-season lawns. Together, they can eliminate a vast number of weeds of varying types. These bundles also include Hi-Yield Spreader Sticker surfactant, which helps the herbicide stick to the leaves and stems of the weed on application. Turf Mark blue spray indicator dye is also included so you can see where you have applied herbicide, so you won’t over-apply or miss areas.
Q. How long should I wait before mowing after applying a post-emergent herbicide?
Mowing timing varies based on the herbicide and weed type. Generally, it's advisable to wait at least two to three days after application before resuming mowing. This allows the herbicide to be absorbed and transported within the target weeds for better effectiveness.
Q. Can I apply post-emergent herbicides when it's raining or about to rain?
Applying herbicides just before or during rain is not recommended. Rain can wash away the herbicide, reducing its efficacy. Ideally, apply herbicides on a dry day when no rain is expected for at least 4 hours to ensure the product has time to work.
Q. Are post-emergent herbicides safe for pets and children?
While many post-emergent herbicides are designed to be safe once they have dried, it's important to keep pets and children away from treated areas until then. Follow the product label instructions for specific safety recommendations.
Organic post-emergent weedkillers like Mirimichi Green Weed and Grass Control are safe to use around pets and children as it is non-toxic, but it’s still best for them to keep away until the product has dried.
Q. Can I use post-emergent herbicides in vegetable gardens?
Using post-emergent herbicides in vegetable gardens requires caution. Only use selective herbicides labeled for use in vegetable gardens. Always check the label for information on specific crops and waiting periods between application and harvest.
Q. What should I do if I accidentally over-apply herbicide?
Over-application can lead to damage to desirable plants and potential environmental harm. If you accidentally over-apply, quickly wash herbicide from non-target plants with water. Preventing the spread of the excess herbicide to other areas is important to minimize the impact.
Q. Can I use post-emergent herbicides near water bodies?
Using herbicides near water bodies requires extra caution due to the potential for contamination. Choose herbicides specifically labeled for aquatic use if you need to control weeds near ponds, lakes, or streams. Always follow label instructions to prevent adverse effects on aquatic ecosystems.
Q. Can I store leftover herbicide for future use?
Storing leftover herbicide depends on the product and its shelf life. Follow the manufacturer's instructions for storage recommendations. Keep in mind that some herbicides may lose effectiveness over time, and improper storage can lead to degradation.
Further reading: Our Step-By-Step Guide for Getting a Golf Course Lawn
So there you have it. Post-emergent herbicides are invaluable tools for controlling unwanted vegetation. Remember that responsible herbicide usage goes beyond the application process. Regular monitoring, integrated weed management practices, and maintaining healthy growing conditions for desired plants also play pivotal roles in long-term weed control success.
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