How soon after Round Up can I scalp?

[schreibdave]

As the title says ...

My plan is to use brand name RU on Thursday. The lawn is growing well and just got a bunch of rain so it's getting long. I want to scalp it in stages and need to get started before it flops over. Thanks

[andy10917]

RoundUp only works on active, green material - not in the soil. So, the more surface area (think blade length) the more that gets transported to the roots. I would not mess with the height. If you absolutely won't sleep if you don't cut it, cut it now, before the RU is applied - and even then I'd leave it at at least 3.5" long. Once the RU is applied, do not mess with the mowing for at least 5 days.

[HoosierLawnGnome]

Make sure it's just glyphosate on the ingredients.

Definitely scalp before it flops. I've always scalped within a week and been amazed how dead it actually was by then before completely brown. Just had that tinge of greying.

[schreibdave]

Andy - i might have to mow before i kill it. Not sure i can stand to look at it at 4+ inches for 5 days. Presumably it will keep growing for a day or 2 after RU? I would mow it to 3.5 which is my normal height.

[andy10917]

If "presumably" means "wishfully", then Yes.

[ken-n-nancy]

Andy - i might have to mow before i kill it. Not sure i can stand to look at it at 4+ inches for 5 days. Presumably it will keep growing for a day or 2 after RU? I would mow it to 3.5 which is my normal height.

If the grass is at a reasonable height before mowing at 3.5" tall before applying glyphosate, you won't have any problems. If the grass were already 8" tall and were "scalped" down to 3.5" there may be an issue, but if it's at about your normal "1/3rd rule" height for mowing, you'll be fine.

Surprisingly, the grass seems to stop growing almost immediately after the glyphosate is applied. When I've done past renovations and had an arbitrary "edge" in the grass where I sprayed glyphosate on one side of the arbitrary (invisible) line, but not on the other, the spray line is evident to a very attentive eye just one or two days after spraying -- even though the grass looks the same on both sides of the line, the grass that was sprayed with glyphosate has stopped growing, and will be one or two days of growth shorter than the grass that wasn't sprayed. The "growth stoppage" is apparent even before a color change can be seen.

I don't know why, but it really seems to me that the grass on which glyphosate has been sprayed stops growing almost right away.

[schreibdave]

Ok. I will probably mow and then spray.

I do have a question about how much RU to use per 1000 sqft. The RU label says 2.5 oz of "Super Concentrate" per 300 ft. That cant be right for a lawn. A gallon should should treat more than that.

I should be able to use 10 oz in 4 gallons of water in my backpack sprayer to do my 3500 sqft front. Don't you think? In the picture below the RU bottle is on the let. Also below is a picture of the label.

[ken-n-nancy]

Looking in my lawn spreadsheet from last year, when I sprayed glyphosate on the front lawn of about 5100 sqft to kill it all off, I used a total of 35oz of 41% glyphosate in 18gal of water applied over 5100sqft. I believe I sprayed in two complete passes in opposite directions. (i.e., covered entire lawn N/S and then again E/W.) I first used a backpack sprayer to get the edges of flower beds and the woods, then our Earthway S25 sprayer for the bulk of the area. I didn't end up having any missed spots.

Apparently, our glyphosate day was 1 year and 3 days ago: viewtopic.php?f=13&t=24374#p326962

[schreibdave]

If my math is right u used one oz of pure glyphosate for every 355sq ft. of lawn.

If i use about 36 oz of my 50% concentrate over roughly 9k sqft that would be a rate of one oz of actual glyphosate per 500 sqft. I guess thats not too far off.

[schreibdave]

How low do I need to go when I scalp? With the help of the neighborhood lawncare contractor it is down to 1.75. Is that low enough or do I need to go lower? In most cases I can see soil between the crowns of the PR clumps.

[HoosierLawnGnome]

As low as you can. 1.75 is fine.

[schreibdave]

As low as you can. 1.75 is fine.

That answer makes me happy. Scalping wet, uneven lawn is not fun. And I have to haul the clippings away - which is a shame.