Purdue Extension Service

Vanderburgh County, Indiana

Crabgrass Control Should Be Applied Soon

By Larry Caplan, Extension Horticulture Educator, Vanderburgh County, IN

For the Evansville Courier and Press, March 11, 2007

If you've been having a problem with crabgrass for the last few years, you may want to take some steps now to reduce the problem. You shouldn't expect to completely eliminate it...that's a little unrealistic; but you can reduce it to manageable levels.

Right now, you should be applying a pre-emergent herbicide (crabgrass preventative). Pre-emergent herbicides work by killing the germinating crabgrass seedling before it can emerge from the soil. These products must be applied before you see any crabgrass; by the time the weed has emerged, most of these products will not work.

There are many different products on the market that will prevent crabgrass from emerging from the soil. The ones that reportedly work best in southern Indiana include dithiopyr (Dimension) and prodiamine (Barricade). The benefit of products with Dimension is that this product does have a little bit of post-emergence activity, so if a few early crabgrass sprouts are already beginning to peak through your lawn, you might still get control. Some sources indicate that applying a second application 6 weeks later will catch any slow-germinating crabgrass plants.

Most of pre-emergent herbicides are combined with fertilizer to make application easier. Unfortunately, this forces you to apply a fertilizer much earlier than Purdue and other universities recommend. Look for a product with low nitrogen (N) and be sure the majority of the nitrogen is a slow release N. These are listed on the label as “slowly water soluble” or “water insoluble. Applying too much fertilizer now will encourage too much growth and could lead to problems later this summer such as poor root growth and disease. Additionally, since spring rains play havoc with mowing schedules, nitrogen fertilization can further complicate your mowing schedule by causing grass plants to grow too fast.

Be sure to read the label carefully when using pre-emergent herbicides. Nearly all of the products available are very damaging to newly seeded lawns, so if you have a choice between overseeding your lawn and applying the herbicide, I would apply the seed.

Remember, the best weed control is a good, thick lawn, obtained by proper seeding, fertilizing, and watering. Setting your mower at a higher setting also controls crabgrass, which does best when it receives lots of sunlight from a scalped or low-cut lawn.

For more information on proper lawn care and the control of crabgrass, contact the Purdue Extension Service at (812) 435-5287.