When to apply pre-emergent

DSM_in_AtlantaJanuary 27, 2013

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.

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dchall_san_antonio(8 San Antonio)

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.

    Bookmark   January 27, 2013 at 8:16PM
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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)?

    Bookmark   January 27, 2013 at 9:35PM
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dchall_san_antonio(8 San Antonio)

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

    Bookmark   January 29, 2013 at 11:28PM
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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

    Bookmark   February 11, 2013 at 2:12AM
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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.

    Bookmark   February 11, 2013 at 7:24AM
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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.

    Bookmark   February 11, 2013 at 9:36AM
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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

    Bookmark   February 11, 2013 at 5:13PM
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serenitylawnservice - thank you for the very informative reply!

    Bookmark   February 13, 2013 at 3:56PM
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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

    Bookmark   November 3, 2014 at 7:22AM
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forsheems(Lexington, NC)

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.

    Bookmark   November 3, 2014 at 10:08AM
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thank you, appreciate your response!

    Bookmark   November 3, 2014 at 12:12PM
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dchall_san_antonio(8 San Antonio)

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.

    Bookmark   November 3, 2014 at 8:26PM
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forsheems(Lexington, NC)

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.

    Bookmark   November 4, 2014 at 10:17AM
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Very useful info given. Thanks a lot!

    Bookmark   November 11, 2014 at 9:28PM
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Is this point in March too late for a preemergent? I am considering applying Corn Gluten Meal in Atlanta

    Bookmark   March 22, 2015 at 12:18PM
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I'm assuming the forsythia have already bloomed in Georgia and that you're kind of in summer at this point. :-)

Technically, it's never too late for a pre-emergent, but anything that's already sprouted won't be touched. I'd say March is completely acceptable as crabgrass (and everything else) will happily sprout into May in your area. Crabgrass will even go much later than that, and for you, it has time to grow, bloom, and seed out.

So yes, apply it. Just don't expect perfection.

    Bookmark   March 22, 2015 at 12:37PM
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BirkdaleSteve(Border of 8b / 9a)

This might draw some criticism from the esteemed dchall (someone who posts very useful information and is VERY knowledgeable), but I'm not 100% sold on the corn meal or corn gluten meal. I believe it is beneficial for well-established lawns; after all, even if it didn't prevent weed germination, at least it's providing good organic material. However, for lawns that are not magazine-cover-worthy (such as mine), I'm not sure the corn meal works as well as the pre-emergents that are non-organic. There are some interesting articles that come up if you search the web, and I'd really like to hear if anyone here has direct experience with both methods.

    Bookmark   March 23, 2015 at 11:43AM
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dchall_san_antonio(8 San Antonio)

This may surprise you but I have experience with both. I found neither chemical nor organic to be effective in the slightest. A couple summers ago I applied 20 pounds per 1,000 of CGM every month all season long. I had as many weeds then as any other time. If I can't hit the timing right by applying every month, then when do you apply??? If you look at the early research out of Iowa State on the effectiveness of CGM, it was not all that good. There was some measurable decrease, but I would be very hesitant to call it "control." As the funnyman Gallagher used to say about his "Sledge-O-Matic", you can even make french fries, but you have to hit that sucker just right. I think getting the timing on CGM is impossible for the average joe.

The last time I tried chemicals was prior to 2002. As I understand it the preem chemicals have come a long way since then. I look to morph for advice on modern preems.

1 Like    Bookmark   March 23, 2015 at 3:22PM
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BirkdaleSteve(Border of 8b / 9a)

dchall, thank you very much for the information! And completely agree - if applying every month didn't help, then that's all I need to hear.

    Bookmark   March 24, 2015 at 10:26AM
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