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I recently purchased a house last year, and am noticing that most of the lawn is weeds. There are a variety of different looking ones, but there is one type that is all over my lawn, probably taking up about 60-70% of it. Can someone tell me what I can use (hopefully safe for grass/lawn since it is everywhere)? I attached a photo below. I've tried BioAdvanced All-in-One Lawn Weed & Crabgrass Killer, but I do not think that is working unless I am possibly not spraying enough on?

Description of first photo: bottom of the picture is basically the same picture I took in the beginning. It is the the beginning of this weed growing in the grass, at the same height as my grass. Top of the picture is the edge of my property going into the woods, this looks like same weed, but obviously in a much more mature grown state since I don't mow that area.

Description of second photo: I tried to pull out just one long strand of the mature grown weed.

Description of third weed: close up of roots.

Description of fourth weed: original picture of weed in my lawn.

bottom of the picture is basically the same picture I took in the beginning. It is the the beginning of this weed growing in the grass, at the same height as my grass. Top of the picture is the edge of my property going into the woods, this looks like same weed, but obviously in a much more mature grown state since I don't mow that area.

tried to pull out just one long strand close up of roots original picture

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    Please do not apply a chemical unless you know exactly what you are trying to control. Likely the product you tried is a mixture of broadleaf contact and crabgrass pre-emergent agents. It is too late in the season for a pre-emergent to work and if your weed is a grass and not a broadleaf then neither component will have any effect. Applying more is just a waste.
    – Colin Beckingham
    Aug 7, 2019 at 13:29
  • Understood, thank you. The guy from Lowe's told me to use that chemical and told me it was a type of crabgrass. He was very dismissive and in a rush, combined with that I haven't seen any positive results or any pictures of crabgrass that look similar to what I have is why I decided to start to doubt his answer and post on here to additional help. I will definitely stop applying my current chemical.
    – Scott
    Aug 7, 2019 at 13:44
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    Good stuff, thanks. In an effort to get at what your problem weed is, could you dig up a tiny patch, wash off the soil and describe what sort of roots you see? Also look for any effort for this plant to go to seed. If you could hint at where you are roughly located that would help the experts here quite a bit.
    – Colin Beckingham
    Aug 7, 2019 at 13:56
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    I am located in Pennsylvania, right outside of Philadelphia. I can try and dig up a patch today after work and attach more pictures. Thank you in advance.
    – Scott
    Aug 7, 2019 at 14:01
  • @ColinBeckingham, sorry about the delay. I just uploaded a picture of the roots. If you need more pictures/better pictures, please let me know.
    – Scott
    Aug 12, 2019 at 1:31

5 Answers 5

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There is a family of weedkillers you can use which are growth factors, or in other words, plant hormones. These cause the weeds to overexert themselves with uncontrolled growth and then die. Some of them act on a metabolic pathway that grasses don't have but most other terrestrial plants do, and these are safe for lawns. A common one is 2,4-D which is in a number of consumer lawn treatments.

I can speak from personal experience that this stuff looks like magic. Weeds don't so much die as appear to just evaporate, and the grass grows as fast as the weeds die off, so for me it almost took me by surprise how rapidly the weeds just weren't there anymore.

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  • Ok thank you. I will try and look into that 2-4-D stuff
    – Scott
    Aug 6, 2019 at 1:13
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    I will add that if the weed is a grass - which was not obvious from the one picture that was on the original post when I answered - this won't be effective.
    – Tom W
    Aug 14, 2019 at 6:49
  • It is definitely a monocot, like grass.
    – stormy
    Sep 3, 2019 at 20:19
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A lot of weeds will simply go away if you mow the grass regularly. After a full season of mowing and ignoring weeds you would have a much better idea of what problem weeds you really have and then be able to decide on a course of action. It's a slow method, but probably quite efficient and environment friendly.

Here is a sample of hairy crabgrass from my yard. hairy crabgrass Note the dense crown of shoots with similar short, wide leaves and fibrous roots, and that the long sideways shoots are rooting at the nodes. Watch the patch to see if it turns a purplish colour as we go into the fall.

What puzzles me is that your lawnmower has a problem getting through - are you sure that the machine is sharp and well adjusted? Penn is too far north for the tropical species of crabgrass as far as I know; they would indeed be tougher. In any case if it is the annual crabgrass then a season or two of mowing will prevent new seeds from forming. Probably your next step is to learn about the various grasses available for lawns and what kind of a lawn you want to end up with. Encouraging those grasses will quickly drive the crabgrass out.

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  • Ok thank you. It isn't causing much harm except that it is so thick that it slows down my lawn mower when I am going over it. I'll keep mowing and maybe next year use pre-emergent to try and help a little
    – Scott
    Aug 6, 2019 at 1:15
  • I agree, your picture looks close to what I have, so maybe it is some type of crabgrass. I believe my lawnmower blade is sharp and in good condition, the lawnmower is only 1 years old. I will keep a close eye on the color, I'm hoping with continued mowing, and maybe some overseeding and fertilizing, it will all go away. Thank you so much for going out of your way to try and solve my problems.
    – Scott
    Aug 12, 2019 at 20:10
  • I just added two more pictures at the top with some descriptions of what the picture is. I noticed in the back end of my property (right against the edge that I mow). Some very similar looking weeds, but they are obviously much longer since I don't mow them. I'm hoping this may hint towards an identification.
    – Scott
    Aug 15, 2019 at 17:33
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I posted this on reddit for additional help, and someone was able to identify the weed. It is actually Japanese Stiltgrass, I will be purchasing herbicide to kill this soon, then will cut the lawn real short and bag everything, then I will try and plant some grass seed before the cold season comes.

https://www.reddit.com/r/lawncare/comments/cw82i2/what_is_this_weedgrass_taking_over_my_lawn/

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  • I do believe you are right, Scott. njaes.rutgers.edu/fs1237
    – stormy
    Sep 5, 2019 at 19:55
  • Congrats on your persistence and finally finding the answer. Ontario does not have this weed yet, but we are on the lookout. Keep in mind the suggestions regarding pre-emergence type herbicides.
    – Colin Beckingham
    Sep 6, 2019 at 4:14
  • I am unfamiliar with pre-emergent herbicides today. Back 30 years ago they were only used by landscape maintenance services. These chemicals LEACH very badly. People find that a few precious trees, perennials and ornamental shrubs die, mysteriously. As a Commercial Pesticide Applicator if I had to use chemicals to solve some problem, that would mean I was not doing a proper job. I had to use a BAND AID to fix the problem I enhanced or caused.
    – stormy
    Sep 7, 2019 at 22:26
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THIS MOST certainly is Japanese Stiltgrass.

There are parallel veins in your plant leaves making it a monocot. Using any herbicide meant to kill broadleafs would have a tough time.

The main thing with broadleaf herbicide is that these plants have BROAD leaves. One is supposed to dampen the lawn before applying these specific herbicides. Broad leaves are able to have more of the herbicide stuck to them than the thin thin bladed grasses. Trimec, is a normal broadleaf herbicid. I don't think it will work well with this 'broadleaf monocot'...

I am thinking that your lawn is a warm season grass. Yes or no? If you had cool season grasses I could easily help you rid yourself. But warm season grasses are extremely different.

Sharpen your blades and COLLECT your clippings!

Additional notes.

This weed has a very shallow and weak root system. This will be easy to control because cool season grasses have huge root systems that can be trained to grow very deep.

These grasses with deep roots are able to resource water 4 to 6" below the surface. This weed can only get water 1/2 " to 1" below the surface. I love cool season grasses. I hate warm season grasses because those grasses are similar to the weeds one wants to control.

Cool season grasses, if you learn to manage them correctly make life with a lawn easy.

Quit worrying about 'killing' this weed en mass. Not going to be pretty at all and you will still need to learn how to WEED PROOF your lawn.

Cutting no lower than 3 to 3 1/2 inches. Get your mower deck raised if necessary.

Watering DEEP. Like down to 4" deep in the soil. Then NOT watering until you see your footsteps on the lawn. The blades of grass you bend stay down. THEN and only then do you water deeply again. Your intervals will be short and then lengthen as you train those roots to grow DEEP. 1" of water per week should be what you expect after the roots are trained. Shallow watering only enhances the weeds. Tall top growth prohibits germination of seeds in the lawn bed. Top growth feeds those big root systems and helps to get them to grow DEEPLY. 4 to 6"

Mow NO SHORTER than 3 to 3 1/2". If you have to, get your mower deck manually changed so that you can cut the grass at this height.

Water deeply, cut the grass no shorter than 3" and you better believe you need to fertilize. 4X per season is normal. Dr. Earth's LAWN fertilizer is spectacular, more expensive but you only need 3X application. Got Mycorrhizae fungal spores and best of all thatch eating bacteria! I was responsible for hundreds of acres of lawns to care for per week. This stuff was worth the extra cost!

Using pesticides, which include herbicide/miticide/fungicides...can cause secondary problems. Mowing high, watering deeply and infrequently, fertilizing properly...will cause YOUR crop to out compete the weeds. Gee, I hope this helps.

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  • Thank you. I believe I am a cool season grass (up in Pennsylvania). I actually found out what it is, I will post the answer to everyone.
    – Scott
    Sep 5, 2019 at 19:03
  • Why would you cut the grass short, Scott? Cool season grasses are my 'thing'. Your grass crop needs photosynthetic top growth to be vital and able to out complete weeds. That is simply done by NOT cutting any shorter than 3" actually 3 1/2 inches is the best height. This feeds your cool season grass roots which are HUGE because of genetics and this can work in your favor saving on water. There is no reason I can see for cutting that topgrowth any shorter than 3 to 3 1/2 inches. NONE. Your grass will need all of the strength it can get as you kill this weed. 2, 4 D, huh?
    – stormy
    Sep 5, 2019 at 20:51
  • Stormy, I obviously don't know what I am doing, so I trust your opinion. I will still try to explain what my random thought process was on why I wanted to cut short. To start out from the beginning, I did read a long time ago and have followed the recommended length of cut when mowing the lawn. So to be clear I have always mowed the lawn on the highest setting on my mower. Here is my reason for cutting short: I almost have no more grass left in my yard. So, I was going to spray the weed killer, let it sit for a week or two, and then cut real short and bag the clippings of the weeds
    – Scott
    Sep 7, 2019 at 0:15
  • The weeds that are basically my whole lawn. Then I wanted to dethatch and pull up anything else that was blocking the soil. Then I was going to plant the grass seed. The reason I "made up these steps" is because I didn't think spraying the weed killer, letting it sit for two weeks, then laying grass seed would work. I didn't think the grass would out compete the weeds, so I wanted to cut as short as I could so the seed can get to the soil. My apologies, I just realized your updated answer. So you are saying, don't even worry about spraying killer? and just overseed, water, and fertilize?
    – Scott
    Sep 7, 2019 at 0:19
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    And I guess in the process of mowing the lawn on the mulching setting, I must've run over a little patch of the stiltgrass, and I just have been spreading it ever since during the mowing session. I aided this weed in major transportation and I can't believe it. Right when I bought the house, I did one run of weed and feed (which I heard isn't that good, so I stopped spending money on it). Other than that, I have never fertilized or watered. Before this stiltgrass, I have always had some broadleaf weeds and such, so I have been trying to maintain them before I did fertilizer and overseed.
    – Scott
    Sep 9, 2019 at 14:25
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It's a weird looking weed. My first thought was bamboo, which might explain why selective weed killers wouldn't work. I don't know what happens when you mow bamboo, but there are some very low growing varieties, and what you said about it making mowing very difficult would hold with this theory. Most weeds are softer to cut than grass. As suggested you would need to show a picture of the root.

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  • Thanks for the feedback. I do not think it is bamboo, but I also have no idea about this stuff. The only reason I say I don't think it is bamboo is because it is spreading/taking over my whole lawn, and I don't "think" bamboo would do that?. I just uploaded a picture of the roots. If you need more pictures/better pictures, please let me know.
    – Scott
    Aug 12, 2019 at 1:30
  • The roots do look like a grass, but not very like the crab grass shown. If the base of the stems are balled, stiff, and woody feeling, it still could be bamboo, I don't know where you are from, so can't comment very well. Oh, try cutting the base of the stem. If it's hollow it's bamboo or a reed or sedge. And of course you could always let a bit grow on in a pot. Is there not already something similar around the edges of the lawn?
    – animartco
    Aug 13, 2019 at 12:25
  • I am from around the Philadelphia Pennsylvania area. I just added two more pictures at the top with some descriptions of what the picture is. I noticed in the back end of my property (right against the edge that I mow). Some very similar looking weeds, but they are obviously much longer since I don't mow them. I'm hoping this may hint towards an identification.
    – Scott
    Aug 15, 2019 at 17:34

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