Kill existing Lawn Weeds with a liquid post emergent herbicide that targets the weed, not your grass.
There are two main types of weeds that are commonly found in lawns. Broadleaf weeds, and Grassy weeds.
- Broadleaf weeds are more obvious. Their leaves aren’t grass like, instead they take on different shapes and textures that stand out in your grass. There are tons of broadleaf weeds but some of the most common are dandelion, clover, chickweed, plantain, and wild violet.
- Grassy weeds are a little harder to identify in your lawn since most of them are actual grasses, just not ones we wish to have in our lawns. These grassy weeds include crabgrass, nutsedge, poa annua, poa trivalis, and many more.
The best way to kill existing lawn weeds is with a liquid, lawn safe, post emergent herbicide. That sentence might scare you but it’s really simple. Spray lawn weeds with a liquid herbicide that will kill the weeds without killing your grass.
Liquid post emergent herbicides work so much better than granular post emergent herbicides.
Spot Treat Using Liquid Herbicide to Kill Lawn Weeds
Spot treating means going around your lawn with a liquid herbicide and spraying just the weeds. There are a lot of products that are safe to use on your lawn. A lot of these products even come with an applicator. The best products to use depend on whether you have cool season grass or warm season grass:
For Cool Season Grass:
There are several great products to choose from and sometimes you’ll want to change products depending on the weed you are trying to kill. But there are 2 products I recommend that will cover most weeds you’ll encounter in your cool season grass:
1. Ortho Weed B Gone Plus Crabgrass Control for spot treating lawn weeds. If you have a lot of weeds consider buying the concentrate here to save some money: Ortho Weed B Gone Concentrate. The concentrate is meant to be mixed in a tank sprayer.
For tank sprayers you can either get a small 1-2 gallon tank or a larger 4 gallon tank. The 1-2 gallon tank is usually fine for spot treating: 1 Gallon Tank Sprayer
Ortho Weed B Gone is designed to disrupt the growth of a lot of different kinds of broadleaf weeds and grassy weeds.
To treat your lawn, I recommend walking your lawn frequently (every week) and spraying any lawn weeds you see. This will help you stay on top of weeds and will prevent them from spreading. Many broadleaf weeds require a follow up treatment.
Also, it is highly recommend you mix a little Surfactant in with the Ortho Weed B gone, or any other liquid post emergent herbicide. The Surfactant helps the herbicide stick to the leaf of the plants. When broadleaf weeds are established they can get a waxy coating on their leaves that makes the herbicide hard to stick to. If you’ve ever been unsuccessful with liquid post emergent herbicides it’s likely this was the problem. Mixing in a little Surfactant can make a big difference. You can purchase Surfactant here: Surfactant
2. Another great post emergent liquid herbicide is Tenacity. The active ingredient in Tenacity is Mesotrione. Mesotrione kills a lot of tough grassy weeds that other herbicides don’t. Some of these include Creeping Bentgrass, Nimblewill, and Poa Annua. These weeds can be a nuisance in cool season lawns and Tenacity is the best selective herbicide to kill them.
Another bonus of Tenacity is if you’re planning on seeding areas of your lawn or planning on a lawn renovation this is a safe product to use. Many other liquid herbicides recommend pausing applications at least a month before seeding. With Tenacity you can apply leading up to your renovation. You can even treat weeds at the same time as seeding (exception with fine fescue, and some other grass types, always read label).
Tenacity does have a couple of drawbacks. For starters it takes awhile to see results. It could take up to 2-3 weeks before weeds die back. Also, because it works by blocking photosynthesis in weeds, you’ll see the weeds turn a bleached white color. This will make weeds stand out as they are dying back. Lastly, you might see some temporary bleaching of your grass. This is usually temporary and grass will eventually green back up.
Mixing Surfactant with the Tenacity will help the herbicide stick to the weed.
For Warm Season Grass:
For warm season grass there are 2 liquid herbicides I recommend mainly because they treat a lot of different weeds and can also be used on several types of warm season grass. Unlike cool season grasses, warm season grasses can have different herbicide tolerances between species so always check labels.
1. For warm season lawns my favorite all around post emergent liquid herbicide is Image Southern Weed Killer. The label says for use on St. Augustine and Centipede grass but it can also be used on other warm season grasses such as Zoysia and Bermuda. This product is a concentrate and should be mixed with water in a concentrate. It will kill a lot of common weeds such as Dandelion, Clover, Chickweed, Dollarweed and many others.
The one downside to the Image Southern Lawn Weed Killer is it’s not the best choice for killing some of the tougher weeds such as Crabgrass, Doveweed, Dallisgrass, and others. If you have these weeds then I’d suggest using Celsius WG. You might have some sticker shock when you see the price of this product but keep in mind it is a concentrate that gets mixed with water so you get a lot of mileage out of it. Chances are this product will last you several seasons.
To treat your lawn with either of these products, I recommend walking your lawn frequently (every week) and spraying any lawn weeds you see. This will help you stay on top of weeds and will prevent them from spreading. Many broadleaf weeds require a follow up treatment. Both products benefit from adding a little Surfactant.
Blanket Spray If There’s a Lot of Lawn Weeds
What if you have so many weeds that spot treating isn’t an option?
If you have a lot of weeds mixed in with your lawn it might seem ridiculous to go around and spray each individual weed.
Instead, you’re better off blanket spraying your entire lawn with your lawn safe liquid herbicide. Blanket spraying usually requires a larger 4 gallon tank sprayer with a handle for pumping: 4 Gallon Tank Sprayer
You simply mix the liquid herbicide with water (according to the blanket application instructions on the label) and walk your entire lawn while spraying. I like to go up and down in rows, usually following my mowing lines.
Prevention with Pre-Emergent Herbicides
Unlike granular post-emergent herbicides, granular pre-emergent herbicides can work very well in preventing lawn weeds from becoming established. I strongly recommend using pre-emergent herbicides at 3 specific times during the year. Check out my custom lawn care program to see what pre-emergent to apply and when.
Pre-emergent herbicides prevent crabgrass, as well as other broadleaf weeds from germinating. Prevention is definitely the best method for dealing with broadleaf weeds.
Chemical Free Ways to Kill Weeds in Lawn
There’s always the manual way, which is very effective if you don’t have that many weeds. There is a great weed grabbing tool that many people use to pull weeds completely out of their lawn, including the weeds root system.
It is especially effective for removing dandelions since dandelions have a long tap root that can be hard to rip out.
Renovate Lawn to Combat Weeds
If your lawn is overwhelmed with weeds you might be convinced you have to rip everything out and start over. Before doing so, consider core aerating and overseeding. Core aerating and overseeding, can drastically improve your lawn.
If you want to go a step further, top dressing your lawn, in addition to core aerating and overseeding is the ultimate lawn renovation.
As usual the best recommendation I can give for combating lawn weeds is sticking to a good lawn care program and maintaining a healthy lawn.
Check Out These Posts Next
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Lawn Care Schedule Using 3 Products
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Leave Grass Clippings on Lawn or Not
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Corey Cormiea says
Where do i find the product “Tenacity” ?
Thomas Clarence says
I appreciate you helping me to understand there are plenty of safe products that can be used to remove weeds. I haven’t paid enough attention to my lawn this summer, and now it is overgrown with weeds and other undesirable plants. It would probably be a good idea for me to get some kind of weed spraying equipment so that I can get my lawn looking good again.
Teri Mccormack says
I just rototilled my lawn and started over. A major task, just for the neighbors weeds to blow over. My lawn is full of clover, and what I believe to be wild violet as well as several others. I haven’t used any chemicals as of yet due to living on a wild life habit. I’ll have to use some preventer if I want a lawn, hand pulling for hours and hours to get an inch is defeating.
feel free to check out my post about getting rid of clover… Also if you think it’s really bad instead of using a rototiller, rent a sod cutter. A sod cutter cuts through the root system so you can easily rake up the clover. It’s way less labor then a rototiller or hand pickingl
Don Gordon says
I have a lawn about 3/4 acres and it is loaded with creeping charley. How do I get rid of the creeping charley?
using Ortho Weed B Gone (active ingredients 2, 4-D) is a great choice for creeping charley!
Years ago I had close to a weed free lawn. It took a lot of work getting there. To maintain it I employed a spot treatment method while mowing. I had a small hand sprayer bottle that I kept the Weed-B-Gone mixture in. I mounted a holder for it to the lawn mower handle and whenever I spotted a weed while mowing, I sprayed it. My current lawn hasn’t reached that point yet and I use a zero-turn so it’s harder to spot the weeds and stop to spray them. I’m still at the blanket spraying point.
That’s a great strategy. I always have ortho weed b gone in a tank sprayer ready to go. Being consistent with spot treating is so key!
William C Zappa says
What is the best way to get rid of dollar weed?
Ortho Weed B Gone (active ingredient 2,4D) will knock out Dollar Weed. Just be careful if you have St. Augustine grass since it can be sensitive to 2,4D. Also, Dollar Weed is pretty easy to pull by hand if you don’t have too much of it.
Hesham Abouwarda says
You’re very welcome!
I seeded a new lawn in spring. It is looking good but I am seeing more and more crabgrass. Should I blanket spray my lawn to make sure I kill all the crabgrass? Can I do it in late July/early August if air temps stay below 90 for a week. Is Tenacity the best bet?
Hi Carl… at this point yes I would recommend applying tenacity but wait until air temperature is below 85 degrees. 90 is too hot and can be damaging. Don’t forget though, crabgrass is going to die off on its own by early fall. Any seeds that it has dropped this past spring and summer will germinate next spring. So the key to your success will be to apply a pre-emergent that contains either Prodiamine or Dimension next spring. But overall if I were you I’d kill off as much crabgrass as you could now (weather permitting) to help stop the amount of seeds being dropped from now until fall. Also, continue to fertilize and take care of your lawn as much as possible. When the weather begins to cool the cool season grass will thrive (assuming we are talking cool season grass) and weeds will die back. This is a great time to establish a thick lawn and thick healthy lawns are great for preventing weeds!
Hi Mark. I live in Denver. Long story short.. I have some well-developed patches of crabgrass in an otherwise healthy lawn. Ortho and Roundup post-emergents haven’t worked on them. I was all ready to go out and buy the Tenacity “kit” to spray those patches, but saw your comment above about air temperatures. Are you saying wait until our daytime highs are under 85 before applying? Then use the Dimension enhanced fertilizer twice in the spring based on soil temps? Seems logical, just want to make sure I’m following directions! Thanks.
Hi Don! You’re exactly right. Use the Tenacity but avoid applying when temps are above 85. This could mean applying earlier in the morning. Just avoid the heat of the day. Also, you might want to check out buying some Surfactant (you can buy online). It’s relatively cheap. You add in a about a table spoon in with the tenacity water mixture. It helps the herbicide stick to the leaves. This time of years weeds can get a waxy coating and repel the herbicide. That could be why the ortho wasn’t working. Lastly with the Tenacity, be patient. You might not notice some whitening until a week later. Buy two weeks you should see it really starting to turn white. And yes, in the spring is when you want to be ready with your pre-emergent.
Charles Simpson says
Ok hello good morning just wondering how to take care of those other grasses that spread faster than the grass u planted without harming the grass u planted ??? Please get back with me ASAP.
It really depends on where you are and what grasses you are referring to. Where are you located? If you have a cool season lawn then it could be bentgrass in which case you could spray it with Tenacity herbicide.
Hey Mark, I haven’t been very consistent with my preemergent in the past but made a good effort this year to reduce my crabgrass and Dallas grass. I live in North Carolina and have a backyard with zoysia and a front yard with centipede. Is Celsius WG your preferred post emergent herbicide on these two grasses or is there another product I could use to spot treat throughout the summer?
Weed B Gon is definitely the way to go with spot treating, or end of hose concentrate for wider use.
Avoid granular herbicide.
Defiinetrly recommend the use of a Surfactant.
Yes, definitely agree!
Wendy Clark says
I’m in the San Francisco Bay Area and we’ve just had a beating with rain (which we needed), the weeds are appearing early despite the cold temps. I have a lot of old crabgrass and oxalis to deal with. I got some Andersons with barricade to put down even tho the lawn temp is above 55. Now I think I need to attack the weeds with Tenacity too. Which should I use first? I appreciate the lawn info. We’ve had to neglect our lawns out here because of the drought but I’d like get a small lawn back without starting over completely.
Hi Wendy! I’m going to assume you have cool season grass, so if that’s not the case then let me know. I was looking at data from previous years and it does look like you normally just get warmer from here on out. I would say go ahead and apply the Andersons with Barricade now. A week later you can go ahead and spray weeds with Tenacity. Just know that tenacity works way better when the cells of the weeds are more active which is usually in warmer weather but not hot weather. This time of year I’d try to cherry pick a warmer and sunnier stretch of weather before applying the Tenacity. Also, expect to have to do a follow up spray 2-3 weeks later. I also recommend you apply a second round of the Barricade, or some other pre emergent about 5 weeks after your first application. This will give you a nice long period of coverage.
wendy clark says
Yes, I have cool season grass. Thanks so much for the guidance, your site is a great help!