When to apply Crabgrass Preventer?

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I bet this is an annual question. I think I have been applying mine to early, usually after my grass has started to grow and I have mowed it once or twice.
Here is what I found during my quest for knowledge today! I was hoping to find a straight forward answer, like some soil temp, but even that advice varies.
-Start taking your lawn soil's temperature early in the morning. When it reaches 55 degrees, apply crabgrass preventer.
-Apply crabgrass preventer as soon as established tall fescue and Kentucky bluegrass lawns green up and start growing well.
-Crabgrass preventer halts the seed-sprouting process. If applied after this year's crabgrass germinates, it will have no effect. The only exception to this rule is a rather new product - dithiopyr - sold in a herbicide-fertilizer mix called Dimension.
-Apply when temperatures reach around 70 degrees for a consistant period of time, typically for more than 2 or three days.
-Apply in early spring before weeds sprout (before temperatures are regularly in the 80's).
-When the forsythia bushes starting to flower, or the redbud trees start to bud, or before the dandelion weed puffs and spreads. (Hell, I don't have any of these in my yard!)
Anyone want to add their $.02?
Cheers, Jim
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Don't know what zone you're in, but in most northern zones at least, I think the UW-Extension recommendation should apply: Treat for crabgrass with a preemergent product when the forsythia are in full bloom. Around these parts (Zone 5), that should take into account the soil temp, which is the critical point at which the crabgrass seed is ready to germinate.

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I applied crabgrass preventer 7 days ago. The guideline is to apply it within 5 days of seeing the first dandilion blooms. I might see one or two dandilion blooms on my yard, but lots more in the neighborhood--that tells me it's the right time. Today's crabgrass preventer has a slightly different directions than those used years ago. I'm in zone 7 and usually apply the crabgrass preventer close to March 20.
On Tue, 29 Mar 2005 15:36:52 -0600, "Play4abuck"

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There are also several long-handled weed removal hand tools that can help you do the dandilion and crabgrass job without tearing apart your lawn or using toxic chemicals.
Ray
__________________________________________________ Talk about Weeds: World of Weeds www.ergonica.com
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Couldn't agree with you more about dandelions. Pop 'em out as deeply as possible with one of those v-shaped weed diggers and you're well on your way to a dandelion free lawn.
The difficulty of digging out crabgrass, however, is that usually by the time you realize you have it, it's already starting to throw seed (for next year). A preemergent product simply keeps the seeds from growing beyond germination.
Personally, tho, I don't mind any lawn weeds -- as long as the ground isn't bare, all is well -- I'm too busy trying to pull the weeds from the flower garden!!
Suzy in Milwaukee, WI, Zone 5

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S Orth wrote:

Once crabgrass has already started growing, the only tool that can pull out most of it is the Weed Twister. The Weed Twister helps you locate the root systems and twists out most of the roots quite easily. This is the Weed Twister with the double coils, not to confuse it with other tools also called Weed Twister. Using this tool, it may take 2 or 3 seasons before the crabgrass is history. Assuming you don't like crabgrass, of course. If you don't like to mow or eat dandilions, you need to remove the roots since the plants will resprout from old roots every year (perenial).
Ray ____________________________________________________________ Talk about weeds: Ergonica World of Weeds www.ergonica.com
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Why would you want to pull crabgrass? It's an annual. Keep it mowed, and in the fall seed with standard lawn grasses, use fertilizer and lime and get the desired species growing well. Crabgrass is intolerant of shade and a warm weather species, so if you get the standard northern cool species grasses well established, there's no room for crabgrass.
Dandelions, however, are perennials, and you can dig them if you like.
The secret to avoiding weed establishment is canopy closure... when the soil is well covered with the plants you want, or with a good thick mulch, weeds can't move in.
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