The Ultimate Guide to Fall Weed Control

As the vibrant colors of summer begin to fade and the air turns cooler, it's time for homeowners to shift their focus to fall lawn care. 

Fall is a crucial season for weed control, as it sets the foundation for a healthy, lush lawn in the following year. Weeds can be particularly aggressive during this period, taking advantage of weakened grass and fertile soil to establish themselves. Neglecting weed control in fall can lead to a chaotic and weed-infested lawn come spring, making it challenging to achieve that pristine, picture-perfect lawn we all desire.

When it comes to weed control, homeowners have two main options: pre-emergent and post-emergent herbicides. Each type targets weeds at different stages of their growth cycle, offering unique benefits in the battle against unwanted vegetation. Pre-emergent herbicides act as a preventative measure, targeting weed seeds before they germinate and take root. Whereas post-emergent herbicides are designed to tackle existing weeds that have already emerged, with the goal of eliminating them from your lawn.

The Role of Pre-emergent Herbicides in Fall Weed Control

Poa Annua (Bluegrass) grassy weeds in the lawn, weeds in the yard

Pre-emergent herbicides are a class of weed control chemicals designed to inhibit the germination and early growth of weed seeds in the soil. They create a protective barrier on the soil surface or just beneath it, preventing weed seeds from sprouting and taking root. 

These herbicides work by targeting the seeds' delicate radicles, which are the embryonic roots that emerge from the seed during germination. By disrupting the radicle development, pre-emergent herbicides effectively stop the weed seeds from establishing themselves, making them a crucial tool in the fight against fall weeds.

Targeting Weed Seeds Before They Germinate

Fall is the ideal time to apply pre-emergent herbicides because many weeds begin to produce and disperse their seeds during late summer and early autumn. By applying pre-emergent herbicides before the first hard frost, you can intercept these weed seeds just as they're about to germinate, effectively nipping the weed problem in the bud (literally!). 

The preventive nature of these herbicides is what sets them apart from post-emergent treatments, as they provide a proactive defense against weed infestations.

This is particularly important for preventing Poa annua (annual bluegrass) in your lawn.  It’s a difficult weed to control, so it is better to prevent it with pre-emergent than try to fight it after the fact with post-emergent herbicides — especially if you have cool-season grass because there aren’t really any good selective post-emergent herbicides to get rid of Poa annua once it’s in a cool-season lawn.

Ideal Timing for Applying Pre-emergent Herbicides in Fall

Timing is crucial when it comes to using pre-emergent herbicides. Applying them too early or too late can lead to reduced effectiveness and compromised weed control. 

To work out when to apply pre-emergent in the fall, it's best to use herbicides just before soil temperatures reach the appropriate range for weed seed germination. This often happens when soil temperatures are consistently between 60-70°F (15-21°C) for several days. This is usually around late August to early September in the southeast. By monitoring the local climate and soil temperatures, you can determine the perfect timing to apply the pre-emergent herbicide in your area. With that said, a bit early is always better than late.

Selecting the Right Pre-emergent Herbicide for Your Lawn

Numerous pre-emergent herbicides are available on the market, each with its unique active ingredient and targeted weed spectrum. Some herbicides are broad-spectrum and protect against a wide variety of weeds, while others are more specific to certain types of weeds. So you’ll need to identify the primary weeds plaguing your lawn and select a pre-emergent herbicide that is effective against those particular species and safe for your grass type.

Our best fall pre-emergents: 

  • Specticle FLO This liquid herbicide contains Indaziflam, an effective pre-emergent for warm-season lawns that works for up to 8 months. It's about as good as you can get for weed prevention in warm-season grass. Nothing else comes close for preventing Poa Annua in your lawn.

    Specticle FLO is safe for your Bermuda, St. Augustine, Zoysia, Centipede, Bahia, Buffalograss, and Seashore paspalum lawn and controls more than 75 broadleaf and grassy weeds. This is our favorite pre-emergent to use in the fall on warm-season grass.

  • Dithiopyr .15% pre-emergent herbicide with fertilizer 0-0-7. This granular herbicide contains Dithiopyr, effectively preventing the growth of invading weeds and weedy grasses in lawns. It is known for its weed and feed properties without causing harm to the grass.

    It is a highly effective option to prevent the growth of annual bluegrass (poa annua), crabgrass, henbit, hairy bittercress, chickweed, and other annuals in your lawn, but only if you are not seeding or overseeding. It is particularly favored in the fall strategy for longer protection in regions with milder winters, particularly down south. It is safe to use on both warm and cool-season grass varieties.
  • Prodiamine 65 Wdg (brand alternative — Barricade® 65wdg). This pre-emergent is a granular herbicide that you mix with water to become liquid for spraying on your lawn. Prodiamine effectively controls Poa annua (annual bluegrass), crabgrass, and 30 other problem weeds

    One of the significant advantages of Prodiamine is its extended residual activity. Once applied, it can provide weed control for several months, offering continuous protection against weed infestations. After applying Prodiamine, it needs to be watered in to activate its herbicidal properties. This allows the herbicide to move into the root zone, where it can prevent weed seeds from sprouting.

When choosing a pre-emergent herbicide, consider factors such as application method (granular or liquid), duration of effectiveness, and compatibility with your lawn's grass type. Always read and follow the label instructions carefully to ensure proper application and safety. 

And remember, soil temperatures can influence pre-emergent herbicide effectiveness. It is generally recommended to apply the herbicide when soil temperatures are between 60°F and 70°F for optimal results.

 

Tips for Effective Application and Safety Measures

To ensure optimal results and minimize risks associated with pre-emergent herbicide use, consider the following tips:

  • Prepare the lawn: Before applying, mow the lawn to a shorter height and remove debris or thatch. This helps the herbicide reach the soil surface effectively.

  • Proper application rate: Follow the recommended application rate specified on the herbicide label. Applying too little may result in inadequate control, while applying too much can damage your lawn.

  • Even distribution: Apply the pre-emergent herbicide evenly across the lawn using a calibrated spreader or backpack sprayer. Uneven application can lead to inconsistent weed control. If you opt for liquid pre-emergent, use a floodJet spray tip for best results.

  • Watering in: After applying the herbicide, water the lawn lightly to activate the pre-emergent and ensure it reaches the soil.

  • Safety precautions: Wear protective clothing, gloves, and goggles during application. Keep children and pets away from treated areas for 24 hours until the herbicide has dried or been absorbed into the soil.

By understanding the role of pre-emergent herbicides and implementing them correctly in your fall lawn care routine, you can take a proactive step towards a healthier and weed-free lawn.

Identifying Common Fall Weeds

Henbit weeds in the yard

Fall brings its own weed challenges, and identifying the most common invaders is crucial for effective control. Some of the most prevalent fall weeds include: 

  • Annual bluegrass (Poa annua): This grassy weed thrives in cool and warm-season lawns and can quickly become a nuisance due to its prolific seed production.

  • Common chickweed (Stellaria media): A low-growing, broadleaf weed with small white flowers, chickweed can quickly spread and create dense mats in lawns.

  • Dandelion (Taraxacum officinale): Easily recognizable with its yellow flowers and puffball-like seed heads, dandelions are tenacious perennials that can be difficult to eradicate.

  • Henbit (Lamium amplexicaule): A member of the mint family, henbit has purple flowers and spreads rapidly in thin or bare patches of lawns.

  • Annual ryegrass (Lolium multiflorum): Often used as a winter cover crop, annual ryegrass can become a lawn weed, especially in overseeded areas.

  • Creeping Charlie (Glechoma hederacea): Also known as ground ivy, creeping Charlie is a creeping perennial weed with small purple flowers.

Knowing Their Lifecycle and Behavior

Understanding the lifecycle and behavior of these weeds is vital for effective control. Some weeds, like annual bluegrass and annual ryegrass, complete their lifecycle within a single growing season. Others, such as dandelions and creeping Charlie, are perennials, returning year after year from their root systems. Knowing which category a weed falls into will influence the timing and choice of herbicides for control.

Weed Identification and Potential Impact on Lawns

Accurate weed identification is essential to develop an appropriate weed management strategy. Different weeds may require different treatments, so distinguishing between them is crucial. Some weeds can compete with turfgrass for nutrients, water, and sunlight, leading to thinning and patchiness in the lawn. Others, like creeping Charlie, can spread rapidly and smother desirable grass. 

Identifying the weeds in your lawn will also help you tailor your approach to fall weed control. For example, if your lawn is predominantly affected by annual weeds, a strong focus on pre-emergent herbicides may be more effective. On the other hand, if perennial weeds are the main concern, a combination of pre-emergent and post-emergent herbicides may be necessary.

 

Related reading: What types of weeds look like grass?

Mastering Post-emergent Herbicides for Fall Weed Control

Post-emergent Herbicides for Fall Weed Control

Unlike pre-emergent herbicides that target weed seeds before they germinate, post-emergent herbicides are designed to control weeds that have already emerged and established themselves in the lawn. These herbicides can be selective or non-selective: 

  • Selective post-emergent herbicides: These herbicides target specific types of weeds while leaving desirable grass species unharmed. They work by exploiting differences in weed physiology, effectively killing the unwanted plants without damaging the turfgrass. 
  • Non-selective post-emergent herbicides: These herbicides are not specific to certain weeds and will kill any plant they come into contact with. They are best used for spot treatments or when dealing with widespread weed infestations but should be applied with caution to avoid harming the lawn.

Targeting Existing Weeds in Your Lawn

Fall is an ideal time for post-emergent herbicide applications because many weeds are in their active growth phase during this season. As temperatures cool and moisture levels remain relatively high, weeds become more susceptible to herbicides. Targeting them at this stage ensures a higher chance of successful control and reduces the chances of weed reseeding before winter dormancy.

Choosing the Right Selective Post-emergent Herbicide for Your Lawn

When choosing a post-emergent herbicide for lawns, it's essential to consider the specific type of grass you have, whether it's a cool-season or warm-season variety. 

Cool-season lawns

For cool-season lawns like Kentucky bluegrass, fescue, or ryegrass, we recommend the Tenacity and Sedgehammer herbicide kit with surfactant and dye. This kit includes everything you need to tackle weeds in your lawn. It combines two post-emergents, Tenacity herbicide and Sedgehammer herbicide, to effectively eliminate over 50 grassy and broadleaf weeds. Hi-Yield surfactant, which helps increase the absorption, sticking, and translocation of herbicides is also included in the kit, plus a blue marker dye to see where you have applied your weed killer. 

This kit also works on Centipede grass, and the products are also sold separately.

Warm-season lawns

For warm-season lawns such as Bermuda grass, Zoysia grass, or St. Augustine grass, we recommend the Celsius and Certainty herbicide kit with surfactant and dye. Like the cool-season kit, this one also contains two weed killers that won’t kill your grass.  

Celsius® WG Herbicide controls more than 150 different types of weeds in warm-season grass, and Certainty Herbicide will rid your lawn of Poa annua, dandelions, and nutsedge. Together they control over 180 grassy and broadleaf weeds. This kit also includes Hi-Yield surfactant to help kill weeds faster and blue marker dye to show where you have applied the weed killer. 

While this kit is suitable for most warm-season grasses, you should not use it with Bahia grass. All products are available to buy separately.

 

Related: Best Nutsedge Weed Killers

 

 

Timing and Application Techniques for Best Results

As mentioned earlier, fall is an excellent time for these applications, but it's essential to consider factors like temperature, weather conditions, and the growth stage of the weeds. Choose a day with calm weather to prevent herbicide drift and apply the product when the temperature is within the optimal range mentioned on the herbicide label. 

Use a backpack sprayer or a broadcast spreader for even coverage. Backpack or handheld sprayers are ideal for spot treatments, allowing you to target specific weeds without affecting surrounding grass. We highly recommend using Turf Mark blue dye to indicate where you have sprayed. 

Safety Considerations When Using Post-emergent Herbicides

When using post-emergent herbicides, safety should be a top priority. Follow these guidelines to ensure safe and effective application: 

  • Read the label: Carefully read and follow the herbicide label instructions, including proper application rates, safety precautions, and personal protective equipment (PPE) requirements.

  • Spot treat when possible: For minor weed infestations, consider spot treatment to minimize herbicide usage and avoid harming desirable plants.

  • Keep children and pets away: Keep children and pets off the treated area for 24 hours until the herbicide has dried or been absorbed into the soil.

  • Avoid herbicide runoff: Be mindful of herbicide runoff into storm drains or water bodies, as this can harm the environment. Avoid applying herbicides before heavy rain is expected.

  • Dispose of herbicides responsibly: Follow local guidelines for properly disposing of herbicide containers and excess product.

By understanding the role and proper use of post-emergent herbicides, you can effectively combat existing weeds in your lawn and maintain its overall health and appearance.

 

Related reading: The Best Weed Killer Spray for Lawns

Achieving Optimal Results: Combining Pre-emergent and Post-emergent Strategies

Freshly Mown Lawn in a Peaceful Garden

While pre-emergent and post-emergent herbicides can be effective individually, combining both strategies offers several key benefits for fall weed control in lawns: 

  • Comprehensive weed control: By using pre-emergent herbicides to prevent weed seeds from germinating and post-emergent herbicides to tackle existing weeds, you create a two-pronged approach that covers all stages of weed growth. 
  • Enhanced weed management: Certain weeds may escape pre-emergent control or have already established themselves before you applied the pre-emergent herbicide. Post-emergent herbicides allow you to target these missed or early-emerging weeds, ensuring more thorough control. 
  • Targeted treatments: Combining both herbicide types enables you to use selective post-emergent herbicides to target specific weed species while sparing your desired lawn grass. This precision reduces the risk of harming the turf while still effectively controlling weeds. 
  • Long-term weed suppression: Using pre-emergent herbicides in the fall helps prevent weed seeds from germinating and reduces the weed seed bank in the soil. This sets the stage for better weed control in the following growing seasons.

 

Want a Weed-free Lawn? Our Step-by-Step Guide for Cool and Warm-Season Grass

 

Creating a Fall Weed Control Schedule for Maximum Efficacy

To achieve the best results, developing a fall weed control schedule tailored to your lawn's specific needs is crucial. Consider the following steps to create an effective plan: 

  • Lawn inspection: Begin by inspecting your lawn to identify the types of weeds present and assess their severity. This will help you determine which pre-emergent and post-emergent herbicides are most suitable for your situation. 
  • Pre-emergent application: Apply the selected pre-emergent herbicide according to the recommended timing, as discussed earlier. Ensure even coverage of the lawn to create a barrier against weed germination. 
  • Monitoring and post-emergent treatment: Keep a close eye on your lawn throughout the fall season. If any weeds emerge despite the pre-emergent application, use selective post-emergent herbicides for targeted treatments. 
  • Re-application: Some pre-emergent herbicides may provide residual control for a limited period. Depending on the product's duration of efficacy, you may need to make repeat applications to maintain weed prevention throughout the fall season.

 

Related reading: Fall Lawn Care Guide and Tips

 

Factors to Consider When Using Both Herbicides Simultaneously

Compatibility 

Ensure that the pre-and post-emergent herbicides you plan to use are compatible and can be safely applied together. Some combinations may cause damage to the lawn or reduce the effectiveness of one or both herbicides.

Timing and Application 

Space out the application of pre-emergent and post-emergent herbicides according to their individual labels to avoid any potential conflicts or interference.

Safety 

Always follow safety guidelines and precautions when handling herbicides. Use appropriate PPE, keep children and pets away from treated areas, and avoid application on windy days to prevent drift. 

By combining pre and post-emergent herbicides in your fall weed control strategy and adhering to a well-planned schedule, you can create a robust defense against fall weeds, leading to a healthier, more vibrant lawn.

Natural Alternatives for Weed Control in Lawns

While chemical herbicides are effective, some homeowners may prefer to adopt more environmentally-friendly practices for weed control. Natural alternatives offer eco-conscious solutions that work in harmony with the environment. Although they may require more effort and time than chemical options, their long-term benefits contribute to a sustainable and a healthy lawn ecosystem.

Cultural Practices to Prevent Weed Growth

Implementing cultural practices can play a significant role in weed prevention and control. By promoting a healthy and robust lawn, you create an inhospitable environment for weeds to thrive. Some key cultural practices include: 

  • Proper mowing: Mow the lawn at the recommended height for your grass type. A denser lawn shades out weed seedlings and reduces their ability to establish. 
  • Adequate watering: Water deeply and infrequently to encourage deep root growth in the turfgrass while making it harder for shallow-rooted weeds to compete. 
  • Soil aeration: Aerating the soil reduces compaction and improves nutrient uptake by the grass, leading to healthier turf that can better fend off weeds. 
  • Fertilization: Proper fertilization helps maintain a dense, healthy lawn that can outcompete weeds for nutrients. 
  • Overseeding: Overseeding cool-season lawns with high-quality grass seed helps fill in thin areas and creates a thick lawn that chokes out weeds.

 

Related reading: How To Kill Weeds Naturally

 

Organic Herbicides and Their Limitations

For homeowners seeking organic alternatives, there are natural herbicides derived from plant-based or non-toxic substances. Organic herbicides typically work by dehydrating the plant tissues or disrupting cellular membranes. Examples include acetic acid (vinegar-based herbicides), citrus oil extracts, and corn gluten meal. While these options are less harmful to the environment, they may have limitations in terms of effectiveness and persistence. 

  • Limited control: Organic herbicides often provide better results on young, small weeds and may not be as effective against well-established or perennial weeds. 
  • Frequent application: Due to their non-persistent nature, organic herbicides may require more frequent applications than chemical herbicides.

  • Spot treatments: Organic herbicides are more suitable for spot treatments rather than large-scale weed infestations. We recommend the Mirimichi Green Organic Weed Control spray, a fast-acting, non-selective, organic weed killer. This herbicide will damage or kill any plant it comes into contact with, so be careful when applying.

 

Maintenance and Aftercare

Post-Treatment Care to Promote Lawn Health

After implementing your fall weed control strategy, it's essential to provide proper post-treatment care to support the recovery and growth of your lawn. Follow these maintenance tips to maximize the benefits of your weed control efforts: 

  • Watering: Continue to water your lawn deeply and infrequently to encourage strong root growth. Adequate moisture helps the grass recover from herbicide stress and maintains its health. 
  • Fertilization: Apply a balanced fertilizer for your grass type to provide essential nutrients and promote vigorous growth. Avoid heavy nitrogen applications in late fall, as it may lead to excessive weed growth. 
  • Mowing: Maintain the recommended mowing height for your grass species, ensuring you never remove more than one-third of the grass blade at a time. Frequent mowing will help control weed seed heads and promote a dense lawn canopy. 
  • Overseeding: Consider overseeding any thin or bare spots in cool-season lawns with high-quality grass seed. This practice helps fill in gaps and provides additional competition against weeds. 
  • Aeration: If your lawn experiences soil compaction, consider aerating to improve root development and water absorption, creating better conditions for a healthy lawn.

 

Related reading: The Best Lawn Fertilizers to Use This Fall

 

Monitoring Weed Re-emergence and Addressing Persisting Issues

Even with a robust weed control strategy, some weeds may still persist or re-emerge. Regular monitoring of your lawn is essential to identify any new weed growth and address persistent weed issues. As fall progresses, inspect the lawn every few weeks to catch any weed growth early on. Promptly apply post-emergent herbicides to deal with any newly emerged weeds, ensuring they do not have the opportunity to set seeds or spread further.

Adjusting Weed Control Strategies for Future Seasons

Use the knowledge gained from your fall weed control efforts to refine your lawn care plan for future seasons. Keep a record of the types of weeds that were most problematic, the effectiveness of the herbicides used, and the timing of applications. This information will help you make more informed decisions in subsequent years and fine-tune your strategy to better combat specific weed species. 

Additionally, consider rotating herbicides and cultural practices to prevent weed resistance. Frequent use of the same chemical herbicides can lead to weed populations developing resistance, reducing the effectiveness of the treatments. By incorporating different herbicides with varying modes of action and adopting diverse cultural practices, you can minimize the risk of weed resistance.

Do The Work in the Fall for a Weed-Free Spring

Fall weed control is a vital component of maintaining a beautiful and healthy lawn throughout the year. By focusing on pre and post-emergent herbicides, you can effectively manage weed infestations and set the stage for a weed-free spring season. 

With proper planning, application, and post-treatment care, you can achieve optimal results in fall weed control, leading to a lawn that is the envy of the neighborhood.

Browse our full range of weed killers and find one which works for your lawn.