will Round Up kill dormant southern grasses

Hello, I am wondering if Round Up or other similar non selective herbicides will kill St. Augustine and/or Centipede grasses when they are in dormance during the winter. To extend the question, how do these herbicides work exactly? If they are only absoarbed via the leaves, then it seems that maybe the dormant grass leaves would not absoarb the herbicide. Any insight into this is appreciated. Thank you.
JB
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James Bond wrote:

Roundup type herbicides are actually variations on the natural growth hormones, and work by tricking the plants into overextending themselves. AFAIK, they are taken up through roots as well as leaves. Being hormones, they don't last long when the plants die, which is the reason you can replant or reseed with no ill effects about two weeks after the weeds have died.
So the question is whether a dormant plant will take up the hormone, start to grow and die. I suspect not, but that's not a good enough answer for you. I'm sure another poster will tell you what you want to know.
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No, you are confusing glyphosate (Roundup) with 2,4-D (weed killer) and 2,4,5-T (brush killer)
2,4-D is a growth hormone that stimulates the plant to grow so much it kills the plant. It works best on broad leafed herbaceous material except won't work on grasses. That is the reason it is commonly sold as "weed killer" for lawns.
2,4,5-T is also a growth hormone but is much stronger than 2,4-D. It kills perennial woody materials but not grasses. That is the reason it is commonly called "brush killer". Unfortunately, dioxin is a common impurity in cheaper grades of 2,4,5-T.
glyphosate (Roundup) only enters through green tissue (leaves and green stems) and must be transported by the plant to the roots where it kills the roots. It is best applied on mature green plants that are transporting sugars to the roots. It will not affect very young plants or plants that are dormant. It gets neutralized up by the clays in soils and will not affect roots directly. It is broad spectrum and will kill most any plant. It works equally well on all herbaceous materials, grasses and woody perennials.
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Stephen Henning wrote:

thanks for the info.
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Doesn't the label say to apply to growing foliage?
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When we lived in Arkansas, the Gardner came on TV and answered questions. His response for crab grass removal, was to go out in the early spring and look at the yard. As soon as you started seeing grass getting green again, spray it with round up. He said that the crab grass was the first to green up and as long as you sprayed it early, you wouldn't bother your other grass that you want to leave.
Dwayne

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