This blog discusses the best options for managing nutgrass and how to correctly identify it. Nutsedge also known as nutgrass is an aggressive weed that can become a major problem in the summertime. There are two varieties of nutsedge: purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus). Purple nutsedge is ranked the world’s worst weed, whilst yellow nutsedge comes in at number 16! Both varieties are perennial weeds in the sedge family that regrow each year and reproduce in a manner that makes them difficult to manage. Sedges are not grasses and thrive in wet soils. Consequently, sedge problems tend to be worse in years with excessive late-spring and early summer rainfall.
How to Identify Nutsedge
Before you take the steps to eliminate this weed correct identification is crucial. When mowed yellow nutsedge has a very similar appearance to purple nutsedge.
- Identification: Identifying purple and yellow nutsedge can be difficult but the following will help. Nutsedge looks like extra-long grass with three leaves per stalk. Mature yellow nutsedge has bright yellow-green leaves and dark yellow flowers. Purple nutsedge has dark green leaves and dark purple or red flowers. The easiest way to identify nutsedge is to look for its triangular stem which distinguishes them from grasses that have flat or round stems.
Purple nutsedge prefers medium to fine-textured soils and is well adapted to compacted soils. It has brownish-black cylindrical tubers and is susceptible to desiccation. Yellow nutsedge tubers are yellow-beige in colour, are also cylindrical and have a wrinkly appearance when dried. It is intolerant to shading and cold tolerant, but neither thrives under low light conditions. It is commonly found in sandy soils and thrives in non-compacted soils.
The tips of the leaf blades can also be a key method of identifying which is present. Yellow nutsedge has long blades with a tapering leaf tip with the leaves also tending to be “pinched”, forming folded boat-shaped tips. In contrast, purple nutsedge often has a shorter leaf blade that always comes to an abrupt tip that remains flat near the tip of the blade.
Images above courtesy of Tim R. Murphy
Nutgrass root system, rhizomes and tubers.
- Root system: Nutsedge has horizontal underground stems called rhizomes that may grow up to 40cm beneath the soil surface. Attached to these are small tubers that can sprout a completely new plant—meaning that numerous nutsedge plants can grow out of the same root system. A single plant may produce thousands of new tubers every year, resulting in vast patches of nutsedge plants. For example, in one study a single tuber produced 1,900 plants and 7,000 tubers.
- A key means of identifying purple nutsedge is that the tubers form chains. In contrast, Yellow nutsedge tubers are not connected to one another and are therefore easier to control with postemergence herbicides.
Yellow nutsedge tubers. Image courtesy of the University of Illinois.
The majority of purple nutsedge tubers are relatively shallow; 45% of the tubers are within the top 4 cm of the soil profile and 95% found within the top 12 cm of the soil profile (Siriwardana and Nishimoto 1987). With relatively shallow distribution in the soil, frequent tillage was the primary means of controlling nutsedges prior to the development of herbicides.
- Growing season: Nutsedge grows during the late spring and summer. While it varies depending on your specific climate, yellow nutsedge generally appears in early summer and purple nutsedge grows in late summer. Since nutsedge is a perennial plant, it will regrow every year.
- Growing conditions: Nutsedge thrives in moist areas with poor drainage.
We’ve done our research and are sharing it with you:
- The best post-emergent nutsedge options.
- The pros, cons, and price of each one.
- Tips to help you choose the right one for you.
The best post emergent herbicide options for managing nutgrass.
There are many effective post-emergent control options for yellow nutsedge, but few provide long-term control of purple nutsedge.
The key to managing nutsedge species is to make herbicide applications coinciding with the maximum number of emerged nutsedge shoots. This is largely dependent upon soil temperature.
Research carried out at Clemson University found trifloxysulfuron (Monument®), to be the best option for controlling purple nutsedge. Multiple applications control more than 90% of purple nutsedge infestations on the couch for more than 70 days (Blanton et al., 2010).
Although effective, it will likely need several applications for complete removal, as purple nutsedge plants can produce thousands of new tubers each year. Each purple nutsedge tuber can remain viable for three years when supplied with adequate soil moisture. Control has been achieved by turning the soil to expose tubers to sunlight before establishing new turf, as this dramatically reduces the viability of purple nutsedge tubers under dry conditions (Stoller and Sweet, 1987).
Post-emergent options for managing nutgrass.
All the following post-emergent chemicals for managing nutgrass have labels etc. in the turf chemicals section. If you want information on using pre-emergent herbicides check this out. There are two post-emergent control options. The first group relies on foliar contact because they do not possess any soil activity and include bentazone (trade name: Nutmeg®), and glyphosate (trade name: Rapid Fire®). Be aware glyphosate is non-selective so will kill any growing tissue it touches.
The degree of control varies dramatically depending on what you are actually treating. For example, bentazone is more effective on yellow nutsedge (75% control), than purple nutsedge (less than 20% control). Glyphosate has better activity on purple nutsedge (70%) than on yellow nutsedge (55%). Glyphosate will translocate through the plant within 3 days and subsequently kill the foliage and the tuber directly attached to the foliage (Rao and Reddy 1999). The key to controlling or suppressing nutsedge growth with these compounds is ensuring the herbicide contacts the nutsedge foliage.
The second post emergent group for managing nutgrass is using chemicals with both soil and foliar activity. These herbicides include halosulfuron. This is equally effective (85% to 95% control) against both nutsedge species.
Vencill and others (1995) determined that 53 g ai/ha of halosulfuron reduced purple and yellow nutsedge regrowth by at least 96% when applied to the foliage, the soil, or both the foliage and the soil. The number of purple nutsedge tubers was reduced by 50% after consecutive years of halosulfuron applied at 72 g/ha (Webster and Coble 1997).
These work best when nutsedge is actively growing, so aim to apply in periods of warm weather, and with adequate moisture. In contrast, dry conditions will often reduce the degree of control.
Registered Post-emergent options for managing nutgrass.
1. Pro-sedge® (nutgrass and mullumbimby couch)
- Pros: Cheap, can be used on both cool and warm season turf, low water application volume, low odour, complete death within two weeks.
- Cons: can develop resistance if overused, repeat 4-8 weeks later once regrowth is observed, Add non-ionic surfactant at 0.25 to 0.5% (v/v).
- Price: $210/500g
2. 3-D® herbicide (Mullumbimby couch).
- Pros: Can be used on both cool and warm season turf, low odour
- Cons: More effective on yellow nutsedge, rainfast 8 hours.
- Price: $215/10L
3. Monument® (Mullumbimby couch).
- Pros: Also controls numerous broadleaf weeds and cool season grasses,
- Cons: Can only be used on couch and zoysia, Need to add a non-ionic surfactant at 0.25% v/v to the spray mixture, repeat 4-8 weeks later once regrowth is observed, rainfast after 3 hours.
- Price: $173/100ml
4. Nutmeg® herbicide (nutgrass/mullumbimby couch).
- Pros: Excellent resistance rotation option.
- Cons: Need to use a non-ionic surfactant such as Wetspray® 1000, don’t apply to newly seeded turf, rainfast 8 hours, repeat 7-10 days later.
- Price: $210/500g
What are the considerations when carrying out chemical control of nutgrass?
If you use the wrong type of herbicide for your grass type, you risk seriously damaging your lawn. This is why it’s essential to check the herbicide label and confirm it’s compatible with your type of grass. For example, some post-emergent herbicides may only be appropriate for cool-season lawn grasses, while others are made for warm-season grasses.
Can I control nutgrass without using chemicals?
- South African work has shown that yellow nutsedge could be controlled to varying degrees by the allelopathic characteristics of https://www.farmersweekly.co.za/agri-technology/farming-for-tomorrow/allelopathy-test-results/
- Sugar kills nut grass. The best time to do this is in spring as the nut grass begins to sprout.
- Simply sprinkle sugar over your entire lawn and give it a light watering to encourage it into the soil, where it’ll eat away at the nut grass (but leave other types of grass and plant alone). It’s best to do this process three or four times during spring to make sure you get any new growth or hardy plants that survived the first couple of rounds. You can use granulated or powdered sugar sprinkled lightly over your lawn or a molasses spray. (Mix molasses at a rate of 450 mL to 40L of water in a backpack or manual sprayer.) https://www.gardeningknowhow.com/special/organic/using-sugar-to-kill-weeds.htm
- Mechanical removal.
- Maintain a thick healthy cover of healthy grass and maintain this at a higher height of cut than usual. The shade will prevent the nutgrass from germinating.
When is the best time to control nutgrass?
To achieve optimal results, treat your lawn in the late spring or early summer right after the nutsedge nutlets first sprout; when nutsedge is still young, it’s much easier to kill.
For more information on identification and managing nutgrass
Rao AS, Reddy KN. 1999. Purple nutsedge (Cyperus rotundus) and sicklepod (Senna obtusifolia) response to glyphosate mixtures with ALS-inhibiting herbicides. Weed Technology 13:361- 366.
Siriwardana G, Nishimoto RK. 1987. Propagules of purple nutsedge (Cyperus rotundus) in soil. Weed Technology 1:217-220.
Murphy T. R, Sedge Biology and Control in Warm-Season Turf, https://slideplayer.com/slide/1628216/
Stoller, E.W., and R.D. Sweet. 1987. Biology and life cycle of purple and yellow nutsedges (Cyperus rotundus and C. esculentus). Weed Technology 1: 66-73.
Vencill WK, Richburg JS III, Wilcut JW, Hawf LR. 1995. Effect of MON-12037 on purple (Cyperus rotundus) and yellow (Cyperus esculentus) nutsedge. Weed Technology 9:148-152.
Webster TM, Coble HD. 1997. Purple nutsedge (Cyperus rotundus) management in corn (Zea mays) and cotton (Gossypium hirsutum) rotations. Weed Technology 11:543-548.
Webster TM, MacDonald GE. 2001. A survey of weeds in various crops in Georgia. Weed Technology 15:771-790.