Monday, August 23, 2010


Nothing looks worse in a pristine lawn than a patch of crabgrass, with its lighter color green in the summer and purplish hue in the fall. I’ve had quite a few calls and stop-ins at the office asking about ‘crabgrass’. Not every grass brought in was crabgrass, but most of it was. The easiest way to find out which grass you have is to bring in a sample for me to look at. Please bring the whole plant, roots to seed head. The more plant parts the better! Now back to crabgrass. Once crabgrass is identified the next question that arises is how do I kill it?

Most are hoping to hear of a miracle herbicide that will kill the crabgrass and keep it out of the lawn forever. I’m glad to say this product does exist. It just costs up to several hundred dollars an acre, requires multiple applications, and requires a pesticide applicators license to be able to purchase and apply it. Herbicides with names like Drive 75, XLR8, and Tenacity are marketed for professional crabgrass control. The easiest way to get a hold of these herbicides is to contact a lawn care service from the yellow pages, get some quotes and go with the service with the best reputation and price.

So how does the average Joe take care of crabgrass in his lawn? There are some herbicides available through hardware stores and garden centers. On the label they will say something to the effect of ‘kills crabgrass’. If you scour the label for the fine print that says ‘active ingredients’, you will find the word Quinclorac, followed by a percentage. This is the actual herbicide in the product that kills crabgrass. The key to this product is to attack the crabgrass when it is young. Crabgrass begins to emerge in May and June, so this is the best time for a first application of an herbicide. These products will not kill crabgrass unless it is emerged. The best thing to do is scout your lawn once a week when you mow to keep an eye out for crabgrass. Once you spot it, give it a few days to recover from the mowing and apply the herbicide. Don’t mow for a few days after you apply the herbicide. Most of these herbicides are labeled for two applications in one summer. Watch the crabgrass for two to three weeks and, if it’s still growing, spray it again.

Now that herbicides are out of the way, what can a lawn owner do to prevent crabgrass from entering the landscape. The best thing to do is keep a dense healthy lawn. Weeds love open patches in lawns where they have access to light. Open patches pop up where sod is unhealthy, trampled along sidewalks or torn up by pesky dogs that belong to the neighbors. Treating these areas for the diseases or insects causing the problem, and following up with reseeding, will help establish new sod that will keep weeds out. If the patch is in a high traffic area, search the shelves of the local store for a seed that claims it will survive the trampling along the sidewalk.

Vigorous growth of established sod is another way to maintain a healthy lawn. This can be accomplished by fertilizing between June and September, when the fertilizer will stimulate lawn growth and not weed growth like spring applications do. The amount of fertilizer you apply to your lawn depends on how much it actually needs. Don’t go by the number on the back of the package. Your lawn may need more or less fertilizer. At OSU Extension, we have guides on how to take soil samples and where to send them off to for testing. Most garden centers also sell a home test kit that will allow you to test your own soil. These kits won’t be as accurate as lab testing, but should suffice. A good rule of thumb is to take multiple samples from around the entire yard and mix them together thoroughly. Samples should be taken from the three inches below the plant roots.

The easiest way to control crabgrass is to keep it out of your lawn. Maintaining a dense growth of grass with proper fertilization, reseeding, disease and weed control will stop crabgrass from getting a foothold. If you do observe crabgrass in your lawn, apply an herbicide before the crabgrass produces four or more tillers. Hopefully, when next August rolls around, your lawn will be crabgrass free for all the folks driving to the fair to admire. If you have any questions on grass ID, or how to control weeds in the lawn or around your property, feel free to contact me at OSU Extension, Darke County, at 548-5215.

Justin Petrosino, Extension Educator, ANR
OSU Extension, Darke County, Top of Ohio EERA, 603 Wagner Avenue, Greenville, OH 45331

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