Controlling Yellow Nutsedge in Lawns

Control nutgrass with two summer herbicide applications

Brian Jervis: Ask a Master Gardener

Saturday, June 20, 2015

Q: I have used some herbicides on my big crop of nutgrass and it didn’t help. Now it seems to grow twice as fast as my Bermuda. How do I get rid of it? Roy P., Tulsa

A: “Nutgrass” is a common name for the weed nutsedge. There are several weedy sedges, but yellow nutsedge is the one most troublesome in our area. Nutsedge is the plant that grows twice as fast as lawns and whose tops appear within two days after mowing.

The name nutgrass comes from the many small “nutlets” produced underground, each of which may produce a new plant. Although sedges are similar in appearance to grasses, their stems are solid and triangular in shape. This gives rise to the adage “sedges have edges.” Grasses on the other hand have hollow round stems.

Nutgrass is often imported with topsoil, mulch or nursery plants contaminated with nutlets. Nutsedge spreads by nutlets as well as underground roots called rhizomes. This is why it often is found in small groups in areas of a lawn.

Control of nutsedge includes cultural and herbicidal approaches. Pulling the sedge will not remove the rhizomes or nutlets, but can be effective if the plant is removed while young and before nutlets form. Nutsedge thrives in moist soil. Reducing the moisture in an area will help but will not eliminate established plants.

Several effective herbicides are available for yellow nutsedge. Some of the brand and chemical names are Basagran (bentazon), Image (imazaquin), SedgeHammer (halosulfuron) and Spectracide Weed Stop for Lawns Plus Crabgrass Killer (sulfentrazone). These chemicals are safe to use on all of our turfgrasses with the exception of Image. It cannot be used on fescue lawns.

Of these herbicides, SedgeHammer is a little more effective and also the most expensive. However, all of them are beneficial and are recommended.

These herbicides should be used in summer when nutsedge is actively growing.

For best control, most will need to be used twice during the summer, according to the labeled directions. Nutgrass has a waxy coat, so some of these chemicals will need an additive called “spreader sticker,” a soap-like solution that helps it stick to the plant and is widely available.

These chemicals cannot be used among flowers or in the vegetable garden. For these areas, it’s either hand-pulling or, if the weed is isolated in spots, the careful use of glyphosate, found in Roundup and other brands. Glyphosate does not migrate in soil, and most of the preparations are labeled for use around vegetables.

Garden tips

Excessive rain can complicate fertilization of vegetables, ornamentals and lawns. If a quick-release fertilizer was applied before the excessive rains, much of the nitrogen may have been washed into deep soil or drain water. Nitrogen, the first of the three numbers on all fertilizer, is very water soluble. The other two nutrients, phosphorus and potassium, are not very soluble and remained fixed in soil where placed unless the soil particles themselves are washed into drains and streams.

It sometimes is difficult to determine if a fertilizer is quick or delayed-release variety. Look at the label; if it states the fertilizer particles are coated with something such as a polymer, it is delayed.

After the rains have passed, consideration should be made to reapply a nitrogen-only fertilizer if the above situation applies to you.

Don’t over fertilize. Too much nitrogen may be worse than too little. Most plants, such as tomatoes, grow tall, spindly and produce few blossoms and fruits when too much nitrogen is used.

Be aware that too much water in the soil may suffocate roots and cause plants to develop yellow leaves that may fall from the plant. This can easily be wrongly confused with a need for more fertilizer.