Killing Crabgrass 
After It Has Started 

Crabgrass Question from Dave in Atlanta, Georgia

Dave Asked: I really need help killing crabgrass. For ten years I had the best fescue lawn in Atlanta, then came our drought.  This year we have had a lot of rain and my lawn is FULL of crab grass despite having applied a pre-emergence in February. I have little fescue left.  I have a limited budget but want to heavily overseed, but wish not to start from scratch.  I will aerate before overseeding, however I'm wondering if the lawn should be slightly plowed for more surface for the seed.  Any advice will be deeply appreciated.

Answer to Killing Crabgrass
After It Starts

Don't worry, your problem is easily fixable. While killing crabgrass after it has started growing is can be difficult, it can be done.

If you don't already know, the good thing is that crabgrass is an annual plant and dies at the end of each year in the fall. It slows down as temperatures cool and is killed at the first heavy frost. If you can wait, getting rid of crabgrass will be done for you, but that doesn't sound like the direction you want to go. But keep in mind that crabgrass must start from seed the following spring. In your part of the country that would be about mid to late March.

This is important to know: Something fertilizer companies never tell anyone is that frequent, heavy rains will stress preemergence herbicides to the max. Several moderate rains or frequent irrigation won't hurt, but repeated heavy downpours will and decreases the effectiveness of preemergent herbicides. Since they advertise "crabgrass control", they don't tell you the limitations. This is also because most homeowner brands are not as strong as commercial brands so you are already at a disadvantage. 

Do not rototill the grass just for crabgrass. It will then need to be leveled and will bring a lot of seeds to the surface. If your grass is mostly crabgrass and dirt, then you can spray round-up and kill it all, but only close to the time you plant to overseed. It will take about a week to see the grass starting to die back.  Low mow and remove as much grass as possible. Then use a vertical mower, (you cam make one yourself) and scratch the surface so the seed has good contact. 

Available Crabgrass Herbicides

MSMA was the product of choice, but is no longer available to homeowners. It is still available to golf courses, sod farmers and highway maintenance workers. It contains a safe organic form or arsenic, but they found it converts to a harmful form in the soil and was taken off the homeowner market. But it sure is good at killing crabgrass.  

Now a product called Drive XLR8 Herbicide is a good alternate choice. Here is a partial list of weeds controlled located on its label:

Barnyardgrass, Bindweed, Crabgrass (large & smooth), Clover, Dandelion, Daisy, Dollarweed, Foxtail, Kikuyugrass, Signalgrass, Speedwell, Torpedograss, and others

It uses Quinclorac as its active ingredient. Look for several products with that active ingredient if Drive is not available where you live. 

Use a pump chemical sprayer or backpack sprayer product's hose end spray bottle to apply the chemical (Weed-B-Gone with Crabgrass control). This is probably the easiest, ready to spray product.

To eliminate crabgrass, spray your grass so it has a thin film over the grass. You are not trying to water the grass. Wear rubber boots if you have them. This is the easiest method of killing crabgrass that is growing. It may need a second application. You can apply a "sticker-spreader" into the herbicide solution to help the chemical stick to the grass better. 

Facts on Pre-emergent Herbicides

The homeowner brands of preemergents found is Scotts brands are not as good or last as long as commercial brands of preemergents.

Products like Barricade and Dimension are two brands that will give year long protection, but it also depends on the percentage of the chemical in the bag. Anything over .300 of barricade will last season long in most cases. There are other commercial brands as well that may be available to homeowners. If you have a landscape supply store that sell to the public, this is your best chance for finding the best products.

For best results apply the preemergent before the crabgrass germinates. Except for Dimension, which can kill crabgrass in seedling form, the rest must be applied before the seed germinates to be affective. 

If you plan to overseed in the fall, do not apply a preemergent in late summer or fall. It will prevent your seed from germinating. 

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