Last week, I mowed my lawn... again! It is really growing rapidly with all the rain and warm temperatures. As I was mowing I noticed an occasional plant that was a light yellowish-green and about two to three inches taller than the surrounding turf. I knew right away that I was going to have to try to control this weed before it got worse.
Long term control of this weed is difficult for two reasons. First, each plant is perennial – it will grow back for many years if not killed. Secondly, each develops multiple little tubers on its root system, as many as 15 per plant, so if you kill the original parent plant several of the dormant tubers will grow back in its place. Where you had one plant, now you have 5.
Yellow nutsedge is a member of the sedge family although it closely resembles a grass. In fact it is frequently called nutgrass or watergrass. It is a common weed in lawns and landscapes, and can often be found in areas with moist soil. Yellow nutsedge is a perennial plant, meaning the below ground portion of each plant survives the winter and generates new top growth each spring.
When you look at it closely, yellow nutsedge has a unique form and can easily be distinguished from turf grasses and other grassy weeds. The leaf blades are light green and are "V" shaped with a prominent ridge down the center of the leaf blade. Leaf arrangement on the plants is called 3-ranked, meaning the leaves originate from the base of the plant giving the lower stem a distinctive triangle shape.
The leaf blades always seem to grow faster than surrounding grass, sticking up above the turf only a few days after mowing. The root system is shallow and fibrous with small nut-like tubers that serve as food storage organs. Each of these small tubers can sprout and form a new plant.
The best strategy is to kill the new young plants before they have matured enough to develop tubers on their roots. Yellow nutsedge responds to day length; plants are triggered by long days to begin forming tubers. This year the longest day of the year was June 20, so mature yellow nutsedge plants will have begun forming new tubers.
After June 20th, many gardeners are told it’s too late to control nutsedge, but that’s not true. You can still kill individual plants, but realize those mature plants have already formed tubers. When you kill the original parent plant, several new young plants will take its place. Don’t think one application of herbicide will end the problem; continue to make additional applications whenever new plants emerge and kill them before these new young plants can form their own tubers. Eventually repeated applications will provide control. Sedgehammer is the most effective product and is available at many garden centers.
In areas with heavy yellow nutsedge infestation, chemical control may provide the only viable option. Common grass and broadleaf herbicides will not control yellow nutsedge. Specialized herbicides for controlling sedges must be used.
Halosulfuron, sold to homeowners in the product Sedgehammer, is one choice for nutsedge control.
Sulfentrazone is a newer chemical now available to homeowners and is also very effective. Homeowners can find sulfentrazone in products like Bonide Sedge Ender or Ortho Sedge Killer. Sulfentrazone provides some pre-emergence control of the dormant tubers. When they start to germinate and grow, the chemical kills them. Again, you should be able to find this at garden centers with a good chemical selection.
On a side note, sulfentrazone is also effective at killing annual grassy weeds like foxtail and crabgrass, so can be used for multiple purposes. But it is selective and will not damage your lawn grass if used properly, according to label directions.
Gardeners can use both Sedgehammer and Sedge Ender together. Hit the existing plants first with Sedgehammer to kill them. Then apply an application of Sedge Ender to kill tubers that might begin germinating. Plan to work at controlling this weed for several years, so you won't be discouraged. Just keep going after them.
Techniques for Best Herbicide Effectiveness
When applying herbicides, avoid mowing about three days before and after treatment. To ensure adequate herbicide absorption, do not water the lawn for at least 24 hours after product application. Applications should ideally be initiated before June 21, when nutsedge is young, actively growing and is most sensitive to herbicidal control. Once this weed matures, control is difficult regardless of the treatment schedule.
Several applications are needed to provide control no matter which product you use. Follow label directions for reapplications and any restrictions on the total number of applications that can be made in a year.
Mechanical Control - AKA Hand Pulling
If you don't want to use herbicides, you can achieve the same goal by hand-pulling plants. Just make sure you are consistently killing new plants as soon as they emerge, before they have time to develop new tubers. Eventually you will reduce the number of tubers in the soil and the problem will decrease. Repeated applications and consistency are the keys to long term control.
Increasing Lawn Density Can Help
If yellow nutsedge is growing in your lawn, anything you do to encourage a thick healthy turf will reduce the problem. Mow your lawn between 3.0 to 3.5" height throughout the year, mow as often as needed to remove no more than 1/3 leaf height each time, focus on fall fertilization, and provide deep, infrequent irrigation as needed during dry periods. Aerate your lawn in spring and/or fall to reduce soil compaction. All these practices will improve turf health and thus reduce yellow nutsedge.