Kill Weeds In Lawns: Begin With The Basics
If you have a yard, you have weeds. They may lurk in the lawn, thrive under a shrub or flourish in flowerbeds, making weed control a constant battle. It requires patience, persistence and knowledge – of both types of weeds and the weapons you have to eradicate them.
What Is A Weed?
A weed is a plant that’s growing where it’s not wanted. Weeds aren’t something you plant intentionally; they just appear. Often they grow vigorously, outpacing and overrunning desirable plants. There are several types of weeds:
Annual Weed: Completes its life cycle – from germination to setting seed – in one growing season; some annual weeds complete their life cycles in a matter of weeks, producing several generations in a single year.
Fact: Annual weed seeds can lie dormant in soil from 4-40 years.
Examples: Chickweed, Crabgrass, Lamb’s-Quarters, Annual bluegrass
Perennial Weed: Lives for two or more years; plants grow as long as conditions are favorable and frequently die back to soil level with hard frost; new growth emerges at the start of the growing season, originating from roots or stem remains; in warmer regions, some perennial weeds can be green year-round.
Fact: Perennial weeds spread by various means, including seed, stems that root as they creep along or pieces of root.
Examples: Creeping Charlie, Curly Dock, Dandelion, Plantain
Broadleaf Weed: Leaves are broad and flat (not grassy or needle-like).
Fact: Broadleaf weeds are easiest to kill or remove when they’re young and actively growing. Some mature broadleaf weeds develop a layer that makes it difficult for weed killers to penetrate.
Examples: Chickweed, Clover, Dandelion, Henbit
Grassy Weed: Looks and grows in ways that resemble grass; leaves are produced one at a time and look like grass blades.
Fact: Many perennial grassy weeds form rhizomes, fleshy roots that resprout if left behind in soil during hand-weeding.
Examples: Bermudagrass, Crabgrass, Giant Foxtail, Goosegrass, Quack Grass
All About Lawn Herbicides
An herbicide is a chemical used to kill weeds or inhibit plant growth. Anytime you use a weed killer, you’re using an herbicide. Some herbicides have residual properties, meaning they continue to kill weeds for a specified time period following application. There are several types of herbicides:
Non-Selective Herbicide: Kills any green and growing plant, whether or not it’s a weed.
Selective Herbicide: Kills only specific types of growing plants; for example, a selective herbicide may kill broadleaf weeds and not grassy plants, so that you can spray it on broadleaf weeds in a lawn without harming grass.
Pre-Emergent Herbicide: Prevents seeds from germinating or kills germinating seeds before seedlings emerge from soil; must be applied before weed seeds germinate. A common example of a pre-emergent herbicide is a Crabgrass preventer, which prevents Crabgrass seeds from establishing new plants.
Post-Emergent Herbicide: Kills weeds that are actively-growing and have already emerged from soil. It’s an ideal herbicide for spot-treating lone offenders but is often applied to entire lawns. Post-emergent herbicides come in two basic forms – contact and systemic.
- Contact herbicide – only kills the plant parts the chemical touches; ideal for treating annuals and perennial weed seedlings
- Systemic herbicide – absorbed by leaves, stems or roots of a plant and moves throughout the plant, affecting every part; effective on annuals and established perennial weeds; must be applied when weeds are actively growing
Specialized Herbicide: To control some especially challenging weeds, like Nutsedge, Clover, Creeping Charlie or Bermudagrass, you’ll want to choose a specific herbicide that’s been proven to be effective. Ask a local garden center or your local Cooperative Extension System office to learn which herbicides will beat your toughest weeds.
Pre-Emergent Secrets to Success
- Treat the entire area – pre-emergent herbicides create a weed barrier, so if you miss a spot, weeds can sprout there. It’s vital to treat the entire area.
- Water in – most pre-emergents require watering in, even liquid forms applied using a hose-end sprayer. With liquid herbicides, the volume of water used to disperse the weed killer is not great enough to wash the material into soil, where weed seeds lie waiting to germinate. That’s why you have to water after application.
- Use caution – when applying pre-emergent herbicides to newly-seeded lawns – or to areas you plan to seed. Read the label carefully. For most products, the label stipulates how many mowings, after seeding, to wait before application. The label also states how long to wait after application before sowing lawn seed.
Post-Emergent Secrets to Success
- Treat young, actively-growing weeds – they die most easily and create less of an eyesore than mature weeds, which might require repeat applications to completely kill weeds.
- Inspect the lawn frequently – while mowing is a good time to look for new weeds that have germinated and require treatment.
For both pre- and post-emergent herbicides, timing is critical. For post-emergent herbicides, you’ll have the best success spraying young, actively-growing weeds. Mature weeds may require repeated applications for total kill. Most post-emergent herbicides should not be applied to dormant lawns. If applying in spring, wait until the lawn is actively growing and has been mowed at least twice.
With pre-emergent herbicides, you’ll want to apply the chemical prior to the time weed seeds start germinating, which can be spring or fall depending on the type of weed. For example: cool-season weeds, such as Annual Bluegrass, are usually best controlled with a late summer to early fall application. If you apply too early, these herbicides will have degraded and are useless when seeds start to germinate. Most pre-emergent Crabgrass killers remain active in soil for 6-8 weeks. If you apply too late, the herbicide will not affect weeds that have already germinated.
Weed seed germination occurs when soil reaches the correct temperature. The best way to determine the ideal time to apply pre-emergents is to contact your local Cooperative Extension System office or master gardeners, who have access to regional soil temperature data.
Other ways to gauge application time include using bioindicators, such as plants whose growth signals the correct time for application. For instance, in northern climates, spring Crabgrass applications are often timed when Forsythia is blooming, which frequently (but not always) occurs when soil temperatures are in the 50°F range. Another option is to time applications based on the calendar. For example, if you typically apply a pre-emergent herbicide in mid-April with success, then continue that routine.
Of course, you can avoid the issue of proper application timing altogether by purchasing a weed control product that combines both pre- and post-emergent herbicides. This type of product kills existing broadleaf weeds and keeps them from returning for as long as six months.
Spray weeds seed
Since releasing this year’s FREE Guide To Fall Seeding we have had some questions come about spraying weeds now leading up to the seeding. In and this blog post will answer those.
First off, you do NOT have to kill all the weeds. The winter is going to kill them for you and having a few here and there will not get in your way too badly. However, if you have had a big emergence of crabgrass in your lawn (where it is all you can see), you will want to try and knock that back some – mainly so it doesn’t go to seed on you.
It’s probably hard for you to tell, but this lawn here is in Munster, IN and this is 99% crabgrass.
Here is what it looks like up close:
If this is you, you will want to spray this and start knocking it down. Leaving it in there is good because it will help hold your seed in place but for sure, if your lawn is this thick with crabgrass, hose it good with quinclorac , quincept or mesotrione leading up to seeding following the recommendations below.
Note on Details:
I’m going to get highly detailed here because I respect you and your intelligence. You’re smart and therefore you can and should seek to understand these chems so you can get the proper result from using them and have no fear of them. I respect the fact that once you take the time to understand this example, you will be better at discernment of similar questions in the future and thus you will be more confident in your approach and strategy. In other words, I’m not going to talk to you like you’re dumb and just tell you what to do. Instead I’m going to teach you like a professional. I hope you are good with that.
Second, I respect the green industry and the lawn pros who make their living doing this day in and day out. When you use professional formulations of products like the ones listed here, I now view you on their level and that also means we need to stay within the bounds of the label which is the law. If you see YouTubers or social media influencers out there not following the label, including me, you should call them/me out. Everyone makes mistakes here and there, but it’s their reaction to being called out that truly shows their intent. I like to think everyone means well and is willing to admit when they are wrong.
Can I Spray Weeds and Kill Crabgrass Now if I Plan to Seed In September/Fall Time?
This is the most common question and it’s difficult to answer for all of you so I’m going to show you how to find the answer for yourself using 2 examples.
Reading The Label – Quinclorac 75DF
Key: The answer to your question is on the label. Labels of weed control products almost always tell you the wait time until seeding after application. Let’s look at two that you likely may be using.
First one is quinclorac . This is the first choice active ingredient that kills crabgrass that you may be seeing. If your lawn is covered in crabgrass like a carpet – especially through the middle or meaty part of the lawn, you will want to kill it off or at least stunt it really well before seeding.
The formulation most of you have is the “DF” which stands for “dry flowable” which means it’s small granules that you put in water to make a solution to spray. The concentration is 75% quinclorac.
Here’s the trick to reading labels fast. Find the PDF online. Make sure it is the VERY SAME product you have in hand. DoMyOwn is a great resource for this .
Once you pull up the label, hit “command F” on Mac or “control F” on PC and this opens up a search window. Type the word “Seed” in that window and it will reveal how many times that word appears in the label PDF.
Use the down arrows in that window to “scroll” through all the instances where that word appears. As I did this, I found the following very quickly.
So we can see that for certain types of seedings, this product won’t cause any harm at all but we have to scroll down to the tables 1 and 4 to get the details. Table 1 is going to tell us the grass types that are “highly” and “moderately” tolerant and table 4 will tell us the timing of the applications for ANY seeding.
This is where it sometimes gets confusing so follow along with me.
Here is Table 1
So what this is telling us is that you can use Quinclorac 75DF on established grasses listed as “highly” or “moderately” tolerant. That is really all this chart is for. It has nothing to do with seeding, hence the word “established.” But you still have to look at this chart first to find out if you should even use this product in the first place.
It’s main purpose is to tell you that you should not use this product on Bahia, Colonial Bent, Centipede or St Aug, period. Doesn’t matter if you are seeding or not, you should NOT use this product on these grass types. It also warns you about using it in or around fine fescues – they must be part of a blend if you do.
So in our case, where we are thinking about seeding the lawn, if we are planning to seed Bahia grass for example, then this product is out, 100%. No Bueno.
So if you passed the test on this part and are seeding Kentucky Bluegrass for example, then you need to next consult table 4 which is going to give you the timing of seeding both before and after.
Let’s stick with our example of Kentucky Bluegrass and you can see that it’s ok to apply quinclorac to the lawn to kill crabgrass 7 days before seeding or more. So right now, if you are let’s say 2 weeks away from seeding, you are welcome to spray away and kill that crabgrass dead. (note, this product turns crabgrass orange/red in about 6 days. But it takes much longer for the crabgrass to fully break down so likely some of it will still be there when you seed, just red and dead).
Also of note, if you have crabgrass living after or during your seed grow in, you have to wait 28 days after emergence (when you see it) before spraying. It’s important to understand what mix you are seeding in this case because if you have a tall fescue, bluegrass mixed seed , the tall fescue will emerge in about 10 days but the bluegrass won’t emerge for 18-21 days so you need to wait 28 days AFTER THE BLUEGRASS emerges before spraying quinclorac. If you really want to be safe, wait the 28 days and 1-2 mowings before applying – this adds some extra protection for the late bloomers as mowing encourages new grass to “harden off” quicker.
Reading The Label – Seeding and Tenacity – Mesotrione
( we have the generic which is cheaper FYI)I will throw this one in real quick because it’s a little different. We recommend this product for a pre-emergent application at the time of seeding. It will suppress certain weeds in your grow in. If you are new and inexperienced, DO NOT think you have to use this – your results will be ok without it. But if you do use it, people think they can just spray it anytime they want and this is not true.
You can spray it anytime you want leading up to seed day, and on seed day, but once your seeds germinate, you should NOT spray it again until the new gras has been mowed 2-4 times or 4 weeks whichever is longer.
So to be clear – you can apply this up to seeding, but once the seed germinates (4-5 days for rye, up to 21 days for bluegrass) you should NOT apply it to weeds until the new turf has been mowed 2-4 times or 4 weeks, whichever is longer. This is because baby grass is weak and can’t withstand/tolerate mesotrione .
Reading The Label – Speed Zone – Red Label
This is another weed control I have recommended heavily and they list right on the label in clear printing how long to wait until you seed. Keep in mind, this product has an 85F degree temp restriction anyway so many of you would not be using it in summer, but in case you did, here is the wait time after app before seeding:
Reading the Label – Quincept – New Farm
Ok now just as I make everything seem like it’s as simple as reading the label, NuFarm (who I love) comes in and just leaves it off their Quincept label completely . Maybe someone from NuFarm can Tweet me and let me know why y’all have left this off your label for so many years… is there a typo you have not corrected? I have read and read the label and this is all I can find – it’s all about “spraying after you seed” but nothing about “spraying before you seed.”
You can read that all you want, backward and forward and it only tells you about “after” seeding. And since I have recommended this weed control so heavily this year I feel like I need to provide an answer.
First off, when I worked for TruGreen ChemLawn, Quincept was our go-to weed control for summer and I remember that every year that right around 3 weeks before overseeding time we would get a memo telling us to cut off the Quincept use. The memo would come early but would read “stop spraying Quincept 2 weeks prior to starting your overseedings for customers.”
So that is my first clue as to the reseed window – it comes from my experience.
Next, I found a product that is similar to Quincept in that it has the same active ingredients plus one. That is Q4 Plus . It has very similar concentrations of the active ingredients within the Quincept plus one more. That product says this:
In short, if you are using Quincept, wait a minimum of 14 days after application to throw down your grass seed. I had to use some logic with this one and figured I’d share it just in case you are doing all the research and coming up empty. Now you know.
So there you go, all about reading labels for seeding – hope this has helped you and that your seeding will be successful this season!
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