Managing nutgrass.
This turf blog discusses the best options for managing nutgrass in Australia and how to correctly identify it. Nutsedge also known as nutgrass in the USA is an aggressive weed that can become a major problem in the summertime in both lawns and sports turf. There are two varieties of nutsedge: purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus). Sedges are not grasses and thrive in wet soils and this means that sedge problems tend to be worse in years with late-spring and early-summer rainfall.
The best method for controlling yellow nutsedge is to grow a healthy, dense, stand of turf that can compete with weeds. If only a few yellow nutsedge plants are present, hand pulling will help eliminate the weeds but will not remove the tubers in the soil. This means that they will come back. A Post-emergent herbicide using a “nutgrass killer” is typically required for control since nutsedges are perennial weeds. Purple nutsedge is ranked the world’s worst weed, whilst yellow nutsedge comes in at number 16! As they are perennial weeds that regrow each year it makes them difficult to manage.
What is nutsedge
Before you take steps to control nutgrass correct identification is crucial. When mowed yellow nutsedge has a very similar appearance to purple nutsedge. 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 soils that have a medium to fine-texture and it is well adapted to compacted soils. It has brownish-black cylindrical tubers and is susceptible to drying out. Yellow nutsedge tubers are also cylindrical but are yellow-beige in colour, and have a wrinkly appearance when dried. It is intolerant to shading and cold tolerant. It is common in sandy soils and thrives in non-compacted soils.
The tips of the leaf blades can also be a key method of identifying what is present. Yellow nutsedge has long blades with a tapered leaf tip. The leaves also tend 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.
Nutgrass images courtesy of Tim R. Murphy1Murphy T. R, Sedge Biology and Control in Warm-Season Turf, https://slideplayer.com/slide/1628216/
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. This means that numerous nutsedge plants can grow out of the same root system and a single plant may produce thousands of new tubers every year. In one study a single tuber produced 1,900 plants and 7,000 tubers.
- The main way 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 a post-emergent nutgrass weed killer.
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 cm2Siriwardana G, Nishimoto RK. 1987. Propagules of purple nutsedge (Cyperus rotundus) in soil. Weed Technology 1:217-220.. Becasue of their shallow distribution in the soil, frequent tillage has always been the main way of controlling nutsedges prior to the development of herbicides.
- Nutsedge grows during the late spring and summer. While it varies depending on your specific climate, yellow nutsedge tends to appear in early summer, while 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.
As turf consultants we’ve done our research:
- The best post-emergent selective nutgrass killer killers;
- The pros, cons, and price of each one.
- Tips to help you choose the right one for you.
How to kill nutgrass in Australia?
Your options are going to be to prevent it using pre-emergent herbicides or alterntively to kill it using post emergent herbicides.
Pre-emergent herbicide options:
No pre-emergent herbicides are registered in turf for the control of purple nutsedge. In our article “reasons for pre-emergent herbicide failure” the main one is that the pre-emergent doesn’t actually work against the weed you want to control. For example, Barricade® and Onset 10GR® which both contain prodiamine, do not work against nutsedge. Weeds sprouting from rhizomes, tubers and bulbs are not controlled with pre-emergent herbicides. However, Brecke et al. (2005)3Brecke, B. J., Stephenson, D. O. IV, and Unruh, J. B. 2005. Control of purple nutsedge (Cyperus rotundus) with herbicides and mowing. Weed Technol. 19:809–814. determined that pre-emergent applications of S-metolachlor (4.48 kg ai ha-1) reduced purple nutsedge total and viable tuber densities 65 and 69%, respectively.
What are kills nutgrass in turf?
There are many effective post-emergent control options for yellow nutsedge management in turf, but few provide long-term control of purple nutsedge. Be aware that it is really important that you carry out a herbicide resistance strategy by rotating turf chemical groups. The Free Guide to Turf chemicals has more information on chemical selection for nutgrass control. Already in parts of Sydney there is herbicide resistance to the SU herbicides.
The key to managing nutsedge species is to make herbicide applications that coincide with the maximum number of emerged nutsedge shoots. This is largely dependent upon soil temperature.
Research carried out at Clemson University found the sulfonylurea herbicide, trifloxysulfuron (Monument®), to be the best option for purple nutsedge. Multiple applications control more than 90% of purple nutsedge infestations on the couch for over 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 conditions4Stoller, 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..
Post-emergent options for managing nutgrass.
Labels for registered post-emergent chemicals for nutgrass are in the turf chemicals section. Here is more information on using pre-emergent herbicides. There are two post-emergent control options. The first group rely on foliar contact because they don’t have any soil activity. These include bentazone (trade name: Nutmeg®), and glyphosate (trade name: Rapid Fire®). Glyphosate is non-selective so will kill any growing plants it touches.
How successfull your spray is depends on what you’re actually treating. For example, bentazone works better 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 then kills the foliage and the tuber directly attached to the foliage5Rao 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.. The key to controlling or suppressing nutsedge growth using these is making sure that the herbicide contacts the nutsedge foliage.
Halosulfuron
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 others6Vencill 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. determined that 53 g ai/ha of halosulfuron reduces purple and yellow nutsedge by at least 96% if you app,y it to the foliage, the soil, or both the foliage and the soil. The number of purple nutsedge tubers falls by 50% after consecutive years of halosulfuron at 72 g/ha7Webster TM, Coble HD. 1997. Purple nutsedge (Cyperus rotundus) management in corn (Zea mays) and cotton (Gossypium hirsutum) rotations. Weed Technology 11:543-548..
These work best when nutsedge is actively growing, so aim to apply in periods of warm weather, and with adequate moisture. Dry conditions will reduce how well they work
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
FAQ
Does pulling nutgrass out by hand make it worse?
Yes! Pulling out nutgrass by hand will not only not stop it from coming back but will make it worse. When you pull it out by hand you only remove the above-ground leaf material. The nuts and rhizomes remain below the surface. If you don’t kill these the nutsedge will regrow in the same spot. So if you insist on removing this by hand you need to dig down and take all the tubers out.
Removing nutsedge by hand can worsen the problem as pulling it out stimulates dormant tubers to start growing. You can add onion grass and oxalis to the list of weeds you shouldn’t pull out. For help in identifying weeds use our handy weed ID chart.
Is there a pre-emergent for nutgrass?
The answer to this is both yes and no. In Australia there currently isn’t any pre-emergent registered for nutgrass/nutsedge prevention. In the USA dimethenamid-P (a component of Freehand herbicide) and Pennant Magnum (metolachlor) state that they work on yellow nutsedge. No pre-emergents control purple nutsedge. Your best way of preventing nutsedge is to maintain a full and dense turf cover as without light it generally doesn’t become a problem.
How do I permanently get rid 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.
How to manage nutgrass organically
- South African work has shown that yellow nutgrass could be controlled to varying degrees by the allelopathic characteristics of ryegrass. This means that if you overseed turf with a high endophyte perennial ryegrass it will help counter this problem weed.
- Sugar kills yellow nutgrass. The best time to do this is in spring as the nutgrass begins to sprout.
- Simply sprinkle sugar over your entire lawn and give it a light watering to wash it into the soil. Then let it work its magic. The sugar eats away the nutgrass (but leaves everything else 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 hits. 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.)
- Mechanical removal. If you are going to do this you MUST remove the rhizomes and nutlets or it will regenerate.
- 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 treat grass for nutgrass or nutsedge?
To get the best results, treat your lawn in the late spring or early summer right after the nutsedge nutlets first sprout. This is because it’s much easier to kill when it’s still young. Very young plants can be hand weeded or you can use a hoe before they have five to six leaves.
The key to control is stopping the plants from becoming established as they can be a real pain to control otherwise. Shade makes it struggle, so ensuring you have a full turf cover can give good results in stopping it from becoming established. If you need to treat chemically you may want to look at using products such as those based on bentazone such as 3-D herbicide rather than halosulfuron (Prosedge). The reason for this is that so much of the latter has been used that resistance issues have now developed. This means that this chemical no longer works.
Disclaimer
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References
After Graduating from Newcastle University with an Hons Degree in Soil Science in 1988, Jerry then worked for the Sports Turf Research Institute (STRI) before emigrating to Australia in 1993.
He followed this by gaining a Grad Dip in Business Managment from UTS and has worked in a number of managment roles for companies as diverse as Samsung Australia, Arthur Yates and Paton Fertilizers.
He has always had a strong affinity with the Australian sports turf industry and as a result he established Gilba Solutions in 1993. Jerry has written over 100 articles and two books on a wide range of topics such as Turf Pesticides and Nutrition which have been published in Australia and overseas.