Why So Many Crabgrass Preventers . . .

Every manufacturer of crabgrass preventers wants a piece of the pie in the lawn care market. Therefore, when you make your annual trek to the garden center, you are faced with a dozen different products to control crabgrass. Decisions about what to use and in what formulation can be mind-boggling. You may ask the following questions:

"Which crabgrass product is best?"

"Do I buy a crabgrass preventer on fertilizer?"

"How much do I need?"

"When should I apply this?"

These are the correct questions to ask, and with the answers in hand, your visit to the garden center can be more pleasurable. While many of the sales associates have good information available to you, many are not trained well enough to answer your specific questions.

All crabgrass preventers, whether it is on a fertilizer or clay granule, will have a label listing the active ingredient of the herbicide used to control crabgrass. Some may list a trade name, but most will list a (common name).

Every year at the University of Missouri Turfgrass Research Center, we look at crabgrass control. There are several products that perform consistently year after year. The top ranked materials include Ronstar (oxadiazon), Dimension (dithiopyr) and Barricade (prodiamine). These products should give excellent full season control of crabgrass. Other common herbicides include Balan (benefin), Team (trifluralin + benefin) and several trade names that contain pendimethalin. These products are more soluble and can breakdown mid to late summer, but tend to cost a little less. All of these products are available on plain or clay granules; however, most are usually sold with fertilizers for over-the-counter sales to homeowners.

Applications of crabgrass preventers should be made prior to April 15. Applications of fertilizer at this time are also acceptable; therefore, crabgrass preventer on fertilizer does save time with a one-step application. However, the fertilizers used are generally quick-release sources of N-P-K, so a flush of green growth is noticed immediately. Fertilizers of this type will last only two to three weeks before wearing off, while your crabgrass preventer should give control well into the summer.

Fertilizers having nitrogen sources that are 50 to 70% slow-release are best for mid-spring applications. Crabgrass preventers can then be applied separately on a plain or clay granule.

The amount of product to purchase is dependent on the square footage of your lawn and the product you choose to purchase. Most over-the-counter products will specify the area that the contents of one bag will cover. Before purchasing a product, measure your lawn to obtain the accurate square footage that you wish to treat. Then, simply divide your total square footage by the footage specified on the label of the product you wish to purchase to determine the number of bags you require.

Applying these products evenly is the key to successful crabgrass control and uniform color from fertilization. We recommend applying one-half of the material required in one direction and then applying the other half in another direction. This gives a more uniform distribution of crabgrass/fertilizer granules and helps prevent streaks or stripes.

Check the label for the proper amount of water needed for watering in the crabgrass preventer. All crabgrass preventers require about ½" of water to activate the chemical barrier that prevents crabgrass germination. The use of crabgrass preventer does not allow you to do any spring seeding after your crabgrass preventer is in place. Re-seeding intervals are specified on the label as weeks or months required before planting any seed. If spring seeding is needed, then only one crabgrass preventer can be used at the time of seeding - Tupersan (siduron).

Knowing your square footage and the type of crabgrass preventer you prefer will make that trip to the garden center less confusing. We ask that you take care in the application of these products and always read the label.

Brad S. Fresenburg, Extension/Research Associate University of Missouri Turfgrass Research Center