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Crowd out crabgrass with thick, healthy lawn
By JIM MOLL, Extension Cords
Published August 14, 2007
Florida has five species of crabgrass. People often misidentify it as "carpet grass." Whatever we call it, it's still a weed in our lawns.
Some species of crabgrass are annual; others are perennial. The species that would normally die out in the winter survived last winter because of the mild weather.
All varieties of crabgrass produce an abundance of seeds. It has been estimated that one plant can produce 200,000 seeds. Liberty Hyde Bailey, the patriarch of American horticulture and department chairman at Cornell University, was asked how to get rid of crabgrass. He replied, "Die and leave it!" If the man who has been described as "the greatest horticulturist who ever lived" says there is little hope in controlling crabgrass, what is the homeowner to do?
Control boils down to three options:
1. Raise your crabgrass tolerance and accept that there will be some in your lawn.
2. Choose to R&R rid and replant.
3. Attempt to prevent new crabgrass seeds from germinating next year.
Why has crabgrass become so difficult to control? In the late 1990s, a herbicide called Asulox was removed from our arsenal of crabgrass control. The product worked after crabgrass was noticeable in the lawn.
Unfortunately, the most desirable lawns (St. Augustine, Floratam, Bahia, etc.) are warm-season grasses. That fact makes it difficult for chemicals to know the difference between which grass you want to kill and which you want to keep. At present, there is nothing available on the market that will control crabgrass selectively in our lawns.
Do not lose all hope. You can begin taking steps to reduce the problem. Weeds take advantage of dead areas in the lawn. A thick, healthy lawn is your best defense against crabgrass.
Learn to take proper care of your lawn. Mow your lawn at 3 or 4 inches high year-round. Fertilize two to three times during the growing season, which is mid March to mid October. Water only when the leaf blades fold in half lengthwise.
What if you already have crabgrass and you want to get rid of it? It's time for "R&R." I do not mean "rest and relaxation"; it's more like sweat and persistence.
The first R stands for rid. (using Round-Up or similar products like Kleen-Up containing the active ingredient glyphosate). Glyphosate will kill the good grass and the bad grass, because it is nonselective. Two treatments 14 days apart should do a good job. If you do not like the idea of chemicals, hand pulling of crabgrass is another option.
The second R is for replanting. Replant dead areas with sod, rather than seeds or plugs, so you prevent light from reaching the crabgrass seeds that are on the surface of the soil.
An ounce of prevention is worth a pound of cure. Pre-emergent herbicide kills the germinating crabgrass seeds. The timing for applying pre-emergent herbicides is critical. It must be done in winter. Our window of opportunity is between mid January and mid February. Mark your calendar, because your mind won't be on crabgrass at that time of year.
Crabgrass seeds start to germinate when we have five nights above 60 degrees (the nights don't have to be consecutive.) During some winters, this may occur as early as mid January. Other years it could happen as late as mid February. Let the weather, not a specific date, be your guide on when to spread the product.
Always read the entire label before applying any pesticide. Follow the manufacturer's directions exactly regarding the amount to use and interval to repeat application. Until new products are developed for application to home lawns, expect to see a reduction in crabgrass next summer, not elimination.
The use of trade names in this article is solely for the purpose of providing specific information. It is not a guarantee or warranty of the products named, and does not signify that they are approved to the exclusion of others of suitable composition. Jim Moll is the urban horticulture agent for the University of Florida/Hernando County Cooperative Extension Service. He can be reached at firstname.lastname@example.org.