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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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RE: When to apply pre-emergent

Instead of starting a new topic, figured I would post here.

I was wonderig, if applying a pre emregent now, or closer to December, will help prevent crabgrass in the spring?

I thought I read it was a trick some use right before winter. I could be remembering incorrectly.

I am in NJ

Thank you


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RE: When to apply pre-emergent

Crabgrass can germinate in the early fall but will die over the winter in areas where frost is common. That being said, a pre m applied late summer will protect from POA annua and some of the other annuals that tend to germinate in the fall/early winter.

For your area, a pre m app in early March will be your best bet for preventing crabgrass. Depending on the type of pre m you use a second app in May or June might be necessary depending on how long it protects.


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RE: When to apply pre-emergent

thank you, appreciate your response!


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RE: When to apply pre-emergent

You prevent crabgrass like this...

1. Grow dense turf. We can help you with this if we know what kind of grass you have, where you live, and how much shade you have.
2. Water deeply and infrequently. Crabgrass seed germinates when the soil surface remains moist for days at a time. If you allow the soil to go for weeks (or days in the hot summer) between watering, then you should really minimize your crabgrass pressure.
3. Mow high (which gets back to dense grass). Most grasses can be mowed high for maximum density. The exceptions are bermuda, centipede, and creeping bentgrass.

Applying a preem this time of year will do nothing for crabgrass. If you don't follow the plan above, then you will need to apply it every month throughout the growing season. If you do follow that plan, you may never need a preem again. I can't remember having crabgrass.

A couple years ago someone wrote in to thank the forum for the advice (above). He said his neighbor's lawn was almost 100% crabgrass but the weeds stopped at his property line because they could not penetrate his turf.


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RE: When to apply pre-emergent

DCHall makes a very good point and all of what he said is proven however here in central North Carolina mother nature can make deep and infrequent watering a challenge. Typically we see rain every 2 to 3 days here during the prime crabgrass germination period. Even with dense turf it can and will pop up due to mother nature keeping the seed moist. Then come July mother nature goes to very infrequent watering or nothing at all.

Last fall I did a complete reno and applied Prodiamine on March 1st of this year with excellent results. We did have our usual wet spring and even with the pre m and thick turf I still had a few sprouts of crabgrass pop up. Nothing major and these were easily spotted (the light green sprigs could be seen from a mile away in the dark green turf) and hand pulled. All of my neighbors lawns are crabgrass, dallisgrass, and other various weeds. If I had complete control of the watering I don't feel that a pre m would be needed but since mother nature has a mind of her own it's a good idea for my situation. I put down the amount of prodiamine to give me 6 months of protection (it's one of the longer lasting pre m's but must be sprayed on so it's a little more difficult to apply) which covered me through August and was gone by the time overseeding came around in September. This can definitely vary by location so there are a lot of areas that may not need anything. Learning to understand your individual situation and your own lawn is key to making everything work.


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RE: When to apply pre-emergent

Very useful info given. Thanks a lot!


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