Crabgrass/Dimension question

I had a section of lawn that had crabgrass in years past. This spring I used a product that contains Dimension (thanks ahlg). It worked great. I have some stray crabgrass plants that I deal with spot treatment.
Will I ruin my Dimension for next year if I de-thatch this fall/next spring? That is, how long do I have to wait for the crabgrass seeds to finally die before I'm able to dethatch?
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De-thatch this fall, then apply dimension again next spring. What's the question?
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A google search didn't show the effective life of Dimension, but most pre-emergents only work for 2-6 months. My guess is that whether you de-thatch this fall or not you'll need to re-apply dimension next spring. If you de-thatch in the Spring, you'll need to apply Dimension after de-thatching, which could be too late to prevent crabgrass germination.
KB

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Say what? Of course you can't put down pre-emergent in Fall and have it be effective in Spring for crabgrass. And de-thatching takes a day, not two months, so there is plenty of time to de-thatch in Spring, then put down pre-emergent.

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Quote: JL wrote on Thu, 16 August 2007 23:28 ----------------------------------------------------

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I'm just curious. Why would de-thatching interfere with the pre-emergent?
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Richard Thoms President - Top Service Pros, Inc. Connecting Homeowners and Local Service Professionals http://www.TopServicePros.com
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Richard Thoms said:

The pre-emergent creates an invisible "barrier" that the weeds can't poke through. Any distruption of that barrier renders it useless.
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Hmm. That's what about.com says as well. http://landscaping.about.com/od/weedsdiseases/qt/kill_crab_grass.htm I'm a little surprised; I don't know about the commercial stuff, but I use corn gluten as a preemergent, which just inhibits root development, so I never thought about whether "puncturing" it would be a problem.
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It's the same concept. Neither one forms a physical barrier that crabgrass can't grow through. What they do is establish a top layer of soil that crabgrass can't germinate in. If you disturb that layer by dethatching, aerating, etc, you lose the protection.
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snipped-for-privacy@optonline.net said:

The plants, themselves, also aid to the destruction of the barrier. Each one pokes a miniscule hole in the barrier, then dies. After millions of holes are poked, weeds start getting through. It's inevitable. Hopefully, there's not enough time left in the growing season for those plants to reach maturity. =)
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Eggs Zachtly wrote:

[....]
and thus prohibiting those plants from being able to contribute their seed to an almost endless cycle of undesirables reproducing themselves....
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