Roundup not killing the grass?

parafly9August 20, 2007

I don't get it. I rounded up the front yard on Friday. I used the recommended amount - 2.5 oz / gal with the Ortho DialnSpray. Used the Roundup Super Concentrate. Only the part of my lawn along the driveway is sying. The rest of it looks normal still.

I rounded up the backyard on Saturday and we had rain about an hour later (should'a checked the forecast). The roundup says its good for 30 minutes and rain. I did the whole yard again yesterday just for good measure and this time I increased the Ortho DialnSpray to 4oz / gallon just to make sure.

Nothing is dying yet. The only place that even looks mildly stressed is the areas along the walkway and flower beds where I carefully sprayed to avoid killing any plants. Those areas where I probaly put more roundup are dying.

I definately checked the size - its supposed to be 2.5oz / gallon / 300 sq feet. Definately did it right.

Am I being impatient? Shouldn't I be seeing some results here after four days? It's odd that I only see it along the driveway on a 8' wide by 150' long stretch. The rest of it hasn't even dulled in color.

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billhill(z5 MI - KBG)

Give it time. You ARE being impatient. You should not use more pesticide than indicated on the label. Follow label instructions carefully. It may take a week or ten days to get a brown lawn from roundup. Bill Hill

    Bookmark   August 20, 2007 at 9:14AM
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Yeah, you should see something by Day 4. All of the green hadn't yet leeched from the blades in my yard but if you walked through the yard, you could feel it was crunchy and the blades had thinned out from the lack of water in them.

I used a pump sprayer, cheap 18% glyphosate, 3oz per gallon I think.

Here was my yard 4 days after spraying -

    Bookmark   August 20, 2007 at 9:16AM
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It takes a week to work.

    Bookmark   August 20, 2007 at 9:46AM
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Here's the odd thing: I had leftover regular concentrate Roundup in the garage. It said use 6oz / gallon in the ortho dialnspray. I used that, and that grass is dead. That only covered about 500 sq feet though. I bought the Suer Concetrate (use at 2.5oz / gallon) and that doesn't seem to be doing much.

Also - I put down some seed about 4 weeks ago because originally my plan had been to just overseed the existing lawn. Is this seed going to sprout still after I put down my new grass? I don't want it to (obviously). Will the roundup render the seeds "dead" - from what I have read about Roundup it doesn't operate like that.

    Bookmark   August 20, 2007 at 9:51AM
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Billl(z7 nc)

I don't know why roundup lies about their concentrate, but they do. The normal - ready to spray - product is 2%. The concentrate is about 18% and the pro can go up to 50%. 2.5oz/gal sprays 2.5/128 = 1.95% of whatever is in the bottle. 1.95% of 50% pro concentrate gives a final output of 0.98%. That is about half as strong as the premixed version.

    Bookmark   August 20, 2007 at 10:06AM
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Hmm. Good thing on my 2nd go-around I moved the ortho dial to 4 from 2.5. That was yesterday plus it was a nice mild dry day so I hope I will see some results.

I spent almost $170 on Roundup so far. Ugh. I think I might call Roundup and try to get some $$ back for the first $80.

    Bookmark   August 20, 2007 at 10:22AM
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Like I keep saying..
The fastest results and best quality kill is from roundup consumer in the ready to use bottle.
Never again will I waste money on concentrate or some highfalutin commercial roundup.

Last year I used the roundup consumer in a corner of the yard and it was dead by the late afternoon. It smelled like pizza as I always point out.

I have also used Spectracide's ready to use product with better results too and it is a good bit cheaper than roundup.

    Bookmark   August 20, 2007 at 10:25AM
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how wet does it need to get? Does a typical grass plant just need, what, one drop on one leaf for it to kill the plant?
I have almost full pump sprayer (2 gallons?) leftover from earlier I might just use that then later as well.

Hopefully I can avoid RU the lawn twice since this will be my 3rd time over the lawn with Roundup in six days.

    Bookmark   August 20, 2007 at 10:47AM
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egghead2004(5/Central MA)

I used the pro concentrate, the one with the purple letters andf cap, it took about a week fro things to brown up. Last year I used the regular concentrate and it took only 3 or 4 days, go figure.

    Bookmark   August 20, 2007 at 11:02AM
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Yeah same thing ere. The regular concentrate browned up MUCH quicker than the Super.

    Bookmark   August 20, 2007 at 11:12AM
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Strange...I used the roundup concentrate with ortho dial and spray set to six and my grass was pretty much toast in 7-9 days. I had a couple very small patches that weren't completely killed that I went over again. The stuff definately doesn't work in 3-4 hours but if you apply it correctly according to labeling directions (6 ounces per 300 sq feet) and give it a week I would expect at least a 95% total kill. Then you can spot treat with the ready mix stuff.

    Bookmark   August 20, 2007 at 11:14AM
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Concentrate, Ortho sprayer at the stated rate, and four days. Of course, it was 90 at the time and I'd been watering to keep the grass active. This could've had much to do with it.

    Bookmark   August 20, 2007 at 11:22AM
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I'm glad to know I'm not the only one with the same slow results from the concentrates.

Who's got 7-9 days? The squirt bottles say results in as little as 3 hours.

Yes the grass plant needs to be thouroughly wet. Maybe that is the reason since the squirt guns seem to do better at this than pump sprayers. Or maybe it is lack of proper mixing equipment. Possibly mixing the concentrate with water and swirling it around thoroughly is not do it it right.

    Bookmark   August 20, 2007 at 11:37AM
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Along with the 2% glyphosate, my RTU container lists 2% pelargonic acid as an additional active ingredient, maybe that is part of the difference?

    Bookmark   August 20, 2007 at 11:54AM
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I've never had a problem w/ the concentrate. In fact, it's always been highly effective for me. However, I don't use a hose end sprayer. I use a 2 gallon pump sprayer. With that, I'm confident that I'm getting the same concentration from the first drop, to the last. I've just never had that level of comfort w/ a hose end sprayer.

    Bookmark   August 20, 2007 at 11:59AM
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The concentration should alwasy be the same, though, right? I mean if you put down 10 gallons of water you get 25 oz. and if you put down 1 gallon of water you get 2.5 oz, the same concentration. ?

    Bookmark   August 20, 2007 at 12:17PM
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Interesting comparison of herbicides here:

See the discussion of Scythe, which is the other active ingredient in the RTU roundup I have. Looks like this may be responsible for the immediate results.

    Bookmark   August 20, 2007 at 12:17PM
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Parafly9, I'm not sure what you mean.

Thanks to your post I've been reading a bit this afternoon and it seems that the RTU Roundup is 2% glyphosate and 2% pelargonic acid, the 18% concentrate provides slightly less than 1% glysophate and a much smaller amount of diquat (so you can't use it on active vegetable gardens) when diluted to the indicated 6 oz./gallon, and the 50% ("super") concentrate provides slightly less than 1% glysophate and nothing else when diluted to the recommended 2.5 oz./gallon.

I called the 800 number and could not get any real explanation for the differences, was just advised that diluting per label instructions would work. I wonder if they each use different surfactants or something. Hopefully someone with real knowledge of these chemicals can explain why these products are formulated the way they are.

I've re-read the link I posted earlier (, and think it told me quite a bit. Read the whole thing it is very clear, but look closely at the tables on recommended rates and times for application depending on what you are trying to kill. Also note that "Reward" is diquat and "Scythe" is pelargonic acid, and "Roundup Pro" apparently has a greater percentage of glysophate than even the super concentrate, but that shouldn't matter if you look at the percentage of glysophate to apply as described in that table.

Oh, and I saw your note in another thread - I'm a "serial compulsive" myself so can totally relate!


    Bookmark   August 20, 2007 at 6:26PM
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Oh, forgot to mention: both diquat and pelargonic acid show symptoms within hours while glysophate can take a week. So it makes sense that the area you treated with the 18% concentrate (containing some diquat)is showing some damage fast while the other areas are not. If you are trying to kill mostly perennial lawn grasses (except maybe bermuda) it looks like you have applied more than enough, so sit tight and watch the slow death!

In my case my first round was with the 18% stuff and it cooked the grassy annuals almost immediately, but the fine fescue has been hanging on for awhile, but tomorrow is day 7 and I would guess I have 95% kill already.

    Bookmark   August 20, 2007 at 6:51PM
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chad_la(z7 TX)

maybe it was made in china and defective like the rest of the stuff we get from over there. LOL seriously though, ive been using glyphosate and other horticultural chemicals professionally for over twenty years now and the results you describe are quite typical. the best product you can purchase is the 50% + or - a tad from reputable farm supply distributors.

legally i cant suggest anything other than to follow the label instructions to the letter. the product will work at the prescribed rates.

avoid the rain fast roundup or any glyphosate product that contains any other active ingredients. products such as diquat and their kin put in the stuff nowadays are why labels say "visible results in one day". these additions are dessicants and while giving joe schmo homeowner the impression his roundup is working really quickly thats just not the case. all they are doing is chemically burning the target plants. for glyphosate to be most effective you need a vigorously growing healthy target plant. glyphosate is a synthetic plant hormone... internet is filled with pages ad nauseum about how and why it works. you shouldnt really see any effects at all from glyphosate for perhaps four or five days to a week maybe.

any burn to your turf you have this soon is not from the glyphosate, its from the dessicants. if you applied them at an increased rate the grass may even try to bounce back a bit before the glyphosate does its job. some grasses like bermuda are so tenacious multiple sprayings may be required. the only addition to plain glyphosate i suggest (and use myself) is one half ounce dawn dishwashing liquid per gallon of final product. this acts as a surfactant, helping the control agent adhere to the plant surfaces and assist in cutting through the waxy layer all plant leaves have to some degree or another.

best of luck

    Bookmark   August 20, 2007 at 7:17PM
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Well, I did it thursday, today is Tuesday, and I think I am finally just barely starting to see it brown up in some areas. Very lighltly, though. So that's almost five days just to start seeing it.

I was hoping to cut & rake soon. I had 13 yards of compost delivered yesterday to spread around the yard. It was colder last night (50's) so this morning the compsost pile was steaming in the yard haha.

    Bookmark   August 21, 2007 at 8:45AM
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billhill(z5 MI - KBG)

Parafly, If you don't mind, Where did you get your compost, and could you post a picture of your pile of commercial compost. As always, Keep your airspeed up on final. Bill Hill

    Bookmark   August 21, 2007 at 10:04AM
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davidandkasie(Z8 MS)

i hav eto say that RU brand takes longer and costs more for the super concentrate. i buy generic glyphosphate off Ebay for around 60.00 SHIPPED for 2.5 gallons and it works quicker. 2.5 oz to a gallon will kill saplings up to 2 inches thick in a couple doses, grass is dead and gone in 3-4 days at the same application rate.

i spray my lawn every spring and kill it off. i use 1.5 oz to a gallon of water, and it takes around 60 gallons to do the roughly 3 acres i spray. i usually have a little left in the tank after that. but within 5 days the lawn is brown and dead. a week later, teh bermuda is back as thick and green as i want it, but with no weeds.

    Bookmark   August 21, 2007 at 10:49AM
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I got it from a local mulch, loam and compost yard.

It was $30 a yard, so not cheap!

I dont have a pic of it right now - but it just look sliek a brown pile of compost ? The largest pieces in there look like little sticks maybe and they are perhaps 3/4" long and 1/8" wide; that is the largest particles in it.

I'd say it looks a lot like this:

    Bookmark   August 21, 2007 at 10:52AM
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With my experience I would say to put two weeks (2 applications of Glyphosphate) into your project plan for grass killing. I could not imagine a product that will give you a 100% total lawn kill in 3 days? Anyway, I started my lawn kill the first week of August and am now ready to start the mowing and raking this weekend. Then prepare the soil and plant my seeds the following weekend I'm thinking a good lawn renovation is going to take patience and time..

    Bookmark   August 21, 2007 at 11:55AM
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I think though I am walking a fine lie between being too late.

I would really like to seed the lawn on labor day weekend (what's that, a week and ahalf or so)

The problem is I will need probably at least 2 evenings to spread out all the compost and another evening to mow and rake. So say next Wednesday (8/29) I would mow and rake the lawn, then Thursady and Friday spread compost, and Saturday rent the slit seeder and do the yard.

I am alrady getting nervous doing it this late. It's gettin' cold here in the mornings already !

    Bookmark   August 21, 2007 at 12:17PM
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joepyeweed(5b IL)

Weather plays a big factor in how fast round up will work.

Most cool season grasses are actively growing in the spring and the fall, and at these times the round up may kill quicker than when applied in the summer.

Though temperature, sunlight and moisture all play a key role in how quickly round up will work also.

The speed of the kill is not necessarily in direct proportion to the concentration of the application.

    Bookmark   August 21, 2007 at 3:52PM
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Day #6. Grass looks moderately stressed. That's it.

The crabgrass are turning yellow in the center though - is that a sign I am on the cusp of the lawn dying?

    Bookmark   August 22, 2007 at 10:27AM
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Parafly, you are being impatient. Roundup will just begin to look effective by day 6. By day 10 the grass-sized stuff will look mortally wounded, and by day 20 it will be brown. A large bush or whatever will take longer. The plants do have to be growing when you spray them. Very little of what grows around a home will survive a goodly dose of glyphosate.

As to amount, very light overspray, rinsed off within a few minutes, may not kill. As long as most of the leaves get a fair amount on them, and there's no rain or sprinkler for an hour, the typical plant is gonna die.

By the way, Home Depot has a house brand concentrate of just glyphosate.

Glyphosate, once applied, breaks down within a day in the environment.

    Bookmark   August 24, 2007 at 5:56PM
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Parafly, the manufacturers of such glyphosate are without doubt scientists in the strict sense of the word.
They have degrees in chemistry and plant sciences.
So one should be able to trust what they say on the label in describing how the home gardener should make such solution.

You've heard the term...."too much too much".
Or...maybe "too little does nothing".

If one ounce can kill a dozen plants, then it follows that 2 ounces will kill twice that number.

But that aint how it works. If the solution is too strong, then it wont work the way the scientists recommend its use.

Next time you think to apply it by as the label suggests, how the label suggests coverage for the amount and do it, of course, where there is no danger of hitting other plants.

There is an interesting thing about glyphosates....too much does nothing. Too little kills very poorly resulting in having to repeat and repeat and repeat applications.

The surgeon knows when to stop the scalpel.

    Bookmark   August 24, 2007 at 7:56PM
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