Crabgrass Pre-Emergent Timing/Question

14 years ago

As spring starts and the Forsythias begin to bloom, habit tells me it's time to put down a pre-emergent to control crabgrass.

It seems everyone says that Forsythia blooming is an indication of crabgrass germination. It's that time in Maryland.

I'd like to discuss that. It seems to be that crabgrass doesn't do much until it's hot outside. I don't recall seeing the first evidence of crabgrass until June (at the earliest). So, why put down the pre-emergent in March? If someone were to put down one application of Halts, wouldn't it be better to wait until late May so the application would last all summer?

Does anyone have any pictures of crabgrass in April or May?

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Comments (8)

garycinchicago
14 years ago
Terps:

A few points -

Halts (Pendimethalin) also prevents germination of poa annua, which germinates earlier than crab grass.

Pendimethalin has a residual of @ 90 days which takes you into June.

Forsythia bloom at or about a 55 degree soil temperature. Crab crab germinates once temperatures rise above 60 degrees - See http://www.uri.edu/ce/factsheets/sheets/crabgrass.html
The forsythia bloom is just a visual aid to get off the duff and out into the yard doing spring time requirements.
dchall_san_antonio
14 years ago
The beauty of using forsythia is that your conditions are different from the conditions in the next town over. Forsythia is what we call a "whisper of Nature." She is telling you, "It's time!" in Her subtle way. You just have to understand Her language.
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I wonder where these ideas generate from. You have a mix of things going on. The time to apply any preemergent is prior to your yard reacting to the spring time weather. The forsythia is usually the first indication of the events of spring. Thus the earliest blooming of the earliest forsythia is the trigger. You are already late for this year. The "good news" is that crabgrass will germinate under proper watering and sun conditions all summer. Chemical fertilizer should not go down until you mow real grass twice. By waiting you will ensure that you are fertilizing your grass and not your weeds. When you apply has nothing to do with root or leaf growth. I'll tell you what has everything to do with leaf AND root growth, AND it controls your weeds to boot, is setting your mower to the highest setting. By growing longer leaves you will grow deeper roots. Deeper roots can get water deeper in the soil, so you can water more deeply and less frequently. Tall grass shades the soil keeping it cooler and less prone to evapotranspiration of the moisture, so you water less. You don't have to use a weed-n-feed. You don't have to do anything until you mow (tall) twice. Then use regular fertilizer. By then some of the winter annual weeds will be dead anyway. By letting your grass grow up tall, weeds like dandelions will die out. Why? Because the surrounding grass will force the broad dandelion leaves to point up and they don't get enough sunshine. The plant will die. Any seeds that blow off the dandelion will not be able to get down to the surface through the tall grass so no new ones will crop up. And if they did hit the surface, and you did water them daily so they would sprout, the tall grass will provide enough shade that the seedling dandelion will not get enough sunlight to take root. If you fertilize in a few weeks, many of the weeds will be gone by then. Then in two more weeks, a few more weeds will be gone but the remaining weeds will be healthy enough to absorb a spot spray like weed-b-gone. This is a less expensive idea than the weed-n-feed and seems to work better. But if you water infrequently and deeply, and mulch mow at your mower's highest setting, you should not have crabgrass this year regardless of your use of preemergents. Mother Nature can throw you a curve and apply enough water to germinate the crabgrass, but that is not the end of the world. The tall grass will severely curtail any spread and may choke it out. It needs plenty of sun to thrive.
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Last year, the crabgrass pretty much took over a 15x12 foot section of my front lawn. The crabgrass moved in after that section got churned up by a skunk looking for grubs - crabgrass tends to take hold in disturbed soil. I didn't want to use herbicides, especially since I applied nematodes to deal with the grubs. So I waited until the crabgrass was of a size to handle easily and then got on my hands and feet and yanked it all out by the roots. When I was done the entire section was pretty much all open soil, with very little grass surviving. I overseeded and the grass came in very nicely. However, I had no illusions that there were a million seeds in there, which is what prompted my post. This spring, then, I did use the pre-emergent and CGM. I wish they didn't feel that they have to add fertilizer to the preemergent but that's all I could find. I used CGM to further suppress germination but also to try to even out the areas that didn't get pre-emergent/fertilizer. I still ended up with some patches but that's sorted itself out by now. So far, I've not seen any crabgrass in the lawn and the area that I've reseeded looks absolutely wonderful. In fact, it's come in so thick that I've had a bit of a chore trying to mow it with my reel mower. Time to sharpen those blades! :)
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terps02
Original Author
14 years ago
I understand that the forsythia blooms are a signal.

Let me ask another question.

I think the majority of people apply Halts (or any Pre-em) one time in early spring. Let's say Halts lasts 90 days. That means that most people have no crabgrass protection for the entire summer. I think most crabgrass grows in the summer (when it's hot). Thus, a crabgrass problem!

If a homeowner were to apply Halts one time per year, when should he/she do it? Like I said above, I think the majority of people do it right around now. I always have. Now that I think about it a little more, I think it's not the best timing.

If you had to rank these three options in order of best crabgrass prevention, how would you do it? Using Zone 7 as a common location, where the forsythia generally bloom right around the first day of spring.

A) Halts on the first day of spring
B) Halts on the first day of summer
C) Halts on first day of spring and summer

I say C, B, A.

Thoughts?
andy10917
14 years ago
Terps:

I think that you may be crediting crabgrass with being a thinking creature, which it is not. Or you may be thinking that Pre-M "prevents" germination, which it does not - even though the name is "pre-emergent".

Crabgrass seeds germinate when there is adequate moisture (think April showers) and proper soil temperatures. The Pre-M does not "delay" the germination, and the crabgrass seeds can't really "outlast" the Pre-M's effectiveness. The Pre-M works by preventing root formation after the grass has actually germinated. With no root system, it wilts and dies before you even see it. No second chances, no waiting for the Pre-M to lose it's effectiveness. It's germinated and dead. The only crabgrass that makes it is if the conditions for germination don't happen before the Pre-M barrier breaks down. If you want to bet that we might not get 60 degrees and wet weather before 90 days from now, than put down more at the beginning of Summer. I'm saving my money to use the additional Pre-M in very late Summer to prevent the Poa Annua germination period (which will overwinter and be NEXT Spring's headache).
terps02
Original Author
14 years ago
Andy, Thanks.

Maybe I'm not thinking about crabgrass seeds and germination correctly.

How long after "germination" would you expect to see the first sprout?

Do you think that all crabgrass seeds germinate at approx the same time (within a few weeks) or do you think it's spread throughout the warm season?

I think that the first sprout happens within days of germination. I also think that most of the crabgrass that I see is in the mid to late summer. Which makes me think that the seeds germinate throughout the entire season, not just when the soil hits a certain temp.

Can you tell that I'm over analyzing? I'm good at that!
andy10917
14 years ago
I don't think it is spread out by more than a few weeks when conditions are right. Nature doesn't work to spread things out - if crabgrass has a 90-120 day lifespan in which to compete for light, food and water and grow seed for next year, what would the value be in delaying it when delays decrease the chances of success? Think "natural selection" - when conditions are optimal, why wait? For the lower rainfall and stressful heat of June and July, when other grasses are mature and good competitors?
dchall_san_antonio
14 years ago
Crabgrass also needs moisture to sprout. The problem in the early spring is many places get a little rain every day for a week. That's all it takes. If that happens in the summer, and your grass has bare spots, then the crabgrass will sprout then, too. If you grass has filled in and covered the bare soil, then the chances of seeing crabgrass sprouts are a lot slimmer.
larryjep_yahoo_com
13 years ago
I have jsut a few crbgrass plants in my lawn. Very few. NY has had a very wet spring. Is it too late to put a pre-emergent on? And second can it be applied to a wet lawn or even in the rain? Thanks

Crabgrass Pre-Emergent Timing/Question

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