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When to apply pre-emergent

Posted by DSM_in_Atlanta none (My Page) on
Sun, Jan 27, 13 at 17:30

I live in the Atlanta area and we are having a typical winter this year (or lack of one). We had a few days of temperatures near 70 a week or two ago but now we are in the 50's with lows in the 30's. It's supposed to climb to 70 again later this week and drop to the 50's. When should I plan on putting down pre-emergents? Do I wait until it warms up a bit? With the temperatures fluctuating as much as they do it's hard to tell when it's time to start. I think my bermuda is already confused although it is still dormant.


Follow-Up Postings:

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RE: When to apply pre-emergent

This is the age old question. For a long time we have talked about putting it down when the forsythia start to bloom. I'm taking that to still earlier prediction. I'm saying the forsythia bloom due to spring rains on warm soil. So if you get a spring rain that accumulates to an inch, that is the time to put it down - according to me. Remember that rainstorm that blew over the south about a month ago? I believe that was the weedmaker storm for us in South and East Texas. I have had weeds popping up for 3 weeks. I put down preem 3 weeks ago, so I may have been a week late.


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RE: When to apply pre-emergent

Hello dchall,

We got a few inches of rain as well from that storm but it didn't warm up much. This Tuesday we are supposed to have storms and a high of 71. Then Friday the high is 45. Should I apply before it rains or right after? Is there any harm in doing it now versus waiting until the temps are a little more stable (warm)?


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RE: When to apply pre-emergent

No harm except to your wallet. If your soil is still below 50 degrees, you should not be getting weeds.


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RE: When to apply pre-emergent

I would do it now if you haven't already I live in south with Bermuda and I applied a roundup and preemergent mix for my winter weeds that are showing and to treat my summer weeds as well. Needs to be done by no later than end of February... Ideally mid January to first of February


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RE: When to apply pre-emergent

Thanks for the replies. I went ahead and applied the pre-emergent the day after posting this on the 28th of Jan. I will apply again in March.

One thing I also noticed is that I do have winter weeds. I think I screwed up by not putting down a pre-emergent in the fall. I'm still getting the hang of this so lesson learned. I sprayed the winter weeds last week with an Ortho product that you attach to your hose. It didn't seem to make much difference so I may try something else.


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RE: When to apply pre-emergent

Good answers.
Remember applying too late can cause problems.
That is why people who apply it too late cannot re seed because the pre emergence is still active.
Look at the bag to see how long the pre emergence is active. Usually 3 to 4 months.


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RE: When to apply pre-emergent

http://georgiaweather.net/ provides the automated environmental monitoring network for the State. I do fertilization and weed control in the Atlanta area, and I use this system routinely. Weed seed, like any seed, respond to soil temperature changes. Most of the weed activity your seeing now, germinated in Fall. Annual bluegrass (Poa Annua), in similar fashion to fescue cultivars, tends to germinate in late October when the soil temperature drops to around 65 degrees, where as henbit and dead nettle tend to come up with lower soil temperatures (50 to 55 degrees) in November and then begin to thrive once those soil temperature come back around in early Spring.

The focus for Spring pre-emergents in Georgia is annual summer weeds, such as crabgrass, which germinates at a soil temperature of approximately 60 degrees. Depending on the rate used, most pre-emergents remain in the soil for 3 to 4 months, so beginning in mid-February and following up with a second treatment 4 to 6 weeks later should give you plenty of control.
Also, be selective about which product you choose. Active ingredients vary quite a bit in test results on certain weed types. For example, Pendimethalin tests very well for broadleaf weed prevention, but is no where near the results of Prodiamine or Dithiopyr on crabgrass control; yet Pendimethalin is the most common active ingredient in pre-emergents marketing crabgrass control in home improvement stores (mainly because it's cheap). However, the Dithiopyr found in Dimmension herbicide is easily the best crabgrass prevention, but offers poor results on broadleaf weeds. Prodiamine is a product that is often used, because it offers good results across the broadest spectrum of weeds.

Here is a link that might be useful: Serenity Lawn Service


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RE: When to apply pre-emergent

serenitylawnservice - thank you for the very informative reply!


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