Managing nutgrass. 17

How to Manage Nutgrass.

This article is aimed at lawn owners and professional turf managers in Australia who have issues with Nutgrass in the turf surfaces. We discuss how to ID Nutgrass and the best Nutgrass herbicides and Nutgrass killers in Australia. After you read this you will be able to:

• Identify sedge and Nutgrass weeds in Australia.
• Know what conditions favour its growth.
• Know how to manage Nutgrass.

Nutgrass is an aggressive perennial weed that can become a major problem in the summer on lawns and sports turf.

Athough it resembles a grass, it actually belongs to a group of plants called sedges. Sedges thrive in wet soils and this means that sedge tends to be worse when there is late Spring and early Summer rainfall.

Why is Nutgrass a Problem Weed?

Purple and Yellow Nutgrass are a problem weed because:

• Fast growth. Patches of Nutgrass in lawns and turf grass look like they haven’t been mowed for weeks.
• Nutgrass is a perennial weeds and regrows each year.
• Dense, rhizomatous growth habit.
• Prolific reproduction.
• C4 photosynthetic pathway.
• Its difficult to kill all of the tubers.
• Allelopathic properties.

Nutgrass belongs to the genus Cyperus, of which 19 species are native to Australia. Five of these species are commonly found in or around turf grass areas in Australia.

Cyperus is from the Greek kypeiros or the Latin cuperos which mean sedge or rush. Rotundus is the Latin for round and refers to the round tubers you find on the roots.

• Purple Nutgrass (Cyperus rotundus).
• Yellow Nutgrass (Cyperus esculentus).
• Umbrella or flat leaf Nutgrass (Cyperus eragrostis).
• Mullumbimby couch (Cyperus brevifolius).
• Green Kyllinga (Cyperus sesquiflorus).

This article primarily focuses on the control and management of Purple and Yellow Nutgrass in lawns and turf grass. Both of these have tubers which makes them very diffilcult to control.

Distribution of Purple and Yellow Nutgrass.

The distribution maps of Purple and Yellow Nutgrass are courtesy of The Living Atlas of Australia.

Purple Nutgrass vs Yellow Nutgrass.

Purple Nutgrass is ranked the world’s worst weed, whilst Yellow Nutgrass comes in at number 16!

• Purple Nutgrass has a prominent basal bulb just below the soil surface. This produces produces a chain of tubers that can go as deep as 60 cm into the soil.
• The seeds of Purple Nutgrass have a 2 to 10% viability but it has tubers that grow very quickly.
• The seed of Yellow Nutgrass has a viability of 90 to 95%, and germination rates of up to 78%. It has small, slow growing tubers and is more likely to grow in cool climates than Purple Nutgrass.

How to ID Nutgrass.

Before you control Nutgrass, it is important to ID if it is actually a sedge.

• Sedges looks like extra-long grass with three leaves per stalk.
• The easy way to ID sedge is by its triangular stem that distinguishes it from grasses that have flat or round stems.
• Nutgrass prefers moist and wet soils.
• It has a glossy, green leaf and a veined triangular stem. If you run your fingers along the stem, it has a sharp edge because “sedges have edges.”
• Nutgrass has a fibrous root system, a large network of branched tubers, and rhizomes.

Cross section of a sedge plant       showing triangular stem

If you determine that you do have sedge present you need to ID which one. When you mow Yellow Nutgrass it looks very similar to Purple Nutgrass, and it can be very difficult to tell them apart.

Table Showing Differences between Common Turfgrass Sedges.

Purple Nutgrass.

• There are several tubers in chains (over six per chain in some cases).
• Purple Nutgrass prefers soils that have a medium to fine texture and it adapts well to compact soils.
• It often has a short leaf blade that comes to an abrupt tip that remains flat near the tip of the blade.
• Purple Nutgrass has dark green leaves and dark purple or red flowers. The flower head is up to 10 cm in diameter and lightens in colour with age.
• You can identify Purple Nutgrass by its purple colouration on the outer leaves at the base of the plant stem, towards the basal bulb. To see this, strip back one or two
  leaves from the base of the nutgrass shoot.
• This purple colouration persists through several layers of outer leaves, while the inner leaves are light green and then white.
• A single plant produces up to 2,000 new tubers in a single season.
• The first tubers are initiated around four weeks after the plant first appears.

Several Purple Nutgrass plants linked by a network of rhizomes

Individual Yellow Nutgrass tubers

Yellow Nutgrass.

• Yellow Nutgrass tubers are not connected to one another. This makes them easier to control with a post-emergent nutgrass weed killer.
• The tubers of Yellow Nutgrass are cylindrical, yellow to beige in colour, and have a wrinkly appearance when they are dried.
• It is intolerant to shade and cold tolerant.
• It is common in sandy, non compact soils.
• Yellow Nutgrass has long leaf blades with a tapered leaf tip. The leaves tend to be “pinched”, and form folded boat-shaped tips.
• Mature Yellow Nutgrass has bright yellow-green leaves and dark yellow flowers.

Yellow vs Purple Nutgrass flower comparison.

Yellow vs Purple Nutgrass leaf comparison

• Nutgrass grows in the late Spring and Summer. Purple Nutgrass yubers do not tend to sprout at temperatures below 20C, and as the shoots move towards light they form swollen basal bulbs. While the localised climate plays a role, you tend to see Yellow Nutgrass earlier in the Summer, and Purple Nutgrass in the late Summer.
• Shoots, rhizomes and other tubers develop from these basal bulbs.
• Most Purple Nutgrass tubers are relatively shallow. 45% of the tubers are within the top 4 cm of the soil profile and 95% are found within the top 12 cm¹Siriwardana G, Nishimoto RK. 1987. Propagules of purple nutsedge (Cyperus rotundus) in soil. Weed Technology 1:217-220..
• Nutgrass is a perennial plant, it will regrow every year.
• Nutgrass thrives in moist areas with poor drainage.

Here is a list of the best Nutgrass herbicides, selective nutgrass killers to control Nutgrass in lawns and turf grass.

• The pros, cons, and price of each one.
• Tips to help you choose the right one for you.

How to Kill Nutgrass in Lawns and Turf.

Your options are to adopt a cultural control program or chemical treatment. A combination of cultural and post-emergent nutgrass killers and Nutgrass herbicides is going to give the best results.

Table of a Suggested Nutgrass Management Timeline.

The table below is a suggested management timeline for Nutgrass in a temperate zone in Australia. Obviously, there will be variations in the timing depending on where you are but this is a good starting point.

Cultural Control of Nutgrass.

Frosts kill above ground parts but tubers survive and overwinter in the soil. The next season dormant tubers can then either germinate or stay dormant for up to 3 years.

• The best way to control Nutgrass in lawns and turf grass is to grow a healthy, dense turf stand.
• Check your irrigation system to make sure that you are not overwatering or there are no overlaps between irrigation heads.
• Increase mowing heights in stress periods. This is important for cool-season grass in the Summer when Nutgrass is at its most competitive.
• Close mowing doesn’t work as it is very tolerant of low mowing heights.
• Fix poorly draining areas.
• If there are only a few plants, hand pulling helps eliminate Nutgrass but doesn’t remove the tubers. This means that they will return.
• In fact there is a high potential when you hand weed to make the problem worse. With Purple Nutgrass if you break the tuber chains it encourages dormant tubers to sprout.

The key to cultural control of Nutgrass in lawns and turf grass is to manage the tubers. Tubers begin to form 4 to 6 weeks after emergence, so if you limit tuber numbers you control the population.

• Remove small Nutgrass plants in lawns and turf grass before they produce new tubers. This is when they only have 5 to 6 leaves. In the Summer this is around every 2 to 3 weeks.
• If you remove as much of the plant as you can, it forces the tuber to use a new bud to sprout, and uses up its energy reserves.
• If you keep repeating this, and remove new shoots, it eventually depletes the tuber’s energy reserves.
• It takes 60% of its reserves to develop the first plant, and 20% for the second.
• Mature tubers regrow over 3 times.

How to Remove Small Nutgrass Plants.

• Pull the new tubers and the basal bulb out by hand.
• Dig down at least 200 to 350 mm to remove all the plant.
• Monitor the area through the Spring and the Summer and remove any new Nutgrass plants.

Management in New Lawns.

If you want to establish a new lawn or turf area tilling the soil has a major positive impact on Nutgrass management. Repeated cultivation exposes Nutgrass tubers to desiccation, and exhausts their food reserves. This works well in hot, dry climates and should be to a depth of at least 30 cm.

Tilling also breaks apart the chains of tubers that you find with Purple Nutgrass, induces them to sprout and then makes them more susceptible to desiccation. 

If you do this in the right conditions the plants tend to die in around 8 days.

Pre-emergent herbicides.

No pre-emergent herbicides are registered for the control of Purple Nutgrass in lawns or turf grass. In our article “Reasons for pre-emergent herbicide failure” the main one is that the pre-emergent doesn’t actually work against this weed.

For example, Barricade® and Onset 10GR® which both contain prodiamine, do not work against Nutgrass in lawns and turf. You cannot control weeds sprouting from rhizomes, tubers and bulbs with pre-emergent herbicides.

However, Brecke et al. (2005)²Brecke, 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 the total and viable tubers of Purple Nutgrass by 65 and 69%, respectively.

When to Kill Nutgrass?

• Target this weed when new leaf growth is greater than 5 cm. When the leaves are greater than 5 cm is often when it is about to flower and is when systemic non selective herbicides like glyphosate are most effective.
• Nutgrass Herbicide application timing is critical to get good results. It is important to apply herbicides soon after Nutgrass emerges in the Spring. This timing limits the number of rhizomes and tubers the plant is able to produce to further spread.
• If you wait until the middle of Summer it gives the plants time to grow more rhizomes, and tubers to regrow after treatment.
• There are several effective post-emergent control options for Yellow Nutgrass in lawns and turf, but few control Purple Nutgrass.
• It is important to adopt a herbicide resistance strategy and rotate chemical groups. Failure to do this has already meant that Nutgrass is showing resistance to the SU herbicides.

Post-emergent Control of Nutgrass.

Because Nutgrass is a perennial weed your only effective chemical option is to use a post-emergent herbicide.

You will get the best results when you treat Nutgrass while its actively growing, which is typically in the late Spring or Summer. Also all post emergent options work better on young rather than mature plants.

As a good guide target Nutgrass when new leaf growth is greater than 5cm. When the leaves are greater than 5 cm is often when it is about to flower and is when systemic non selective herbicides like glyphosate are most effective.

Herbicide application timing is critical for effective control. It is important to apply herbicides soon after Nutgrass emerges in the Spring. This timing limits the number of rhizomes and tubers the plant can produce to further spread.

If you wait until the middle of Summer it gives the plants time to grow more rhizomes and the tubers to regrow and survive herbicide applications.

Post Emergent Timing for Nutgrass Control.

These products tend to quickly move through the plant. However, you must apply them to Nutgrass before the fifth-leaf stage and ideally at the 3 to 8 leaf stage This is when the plant is drawing energy from its leaves to the new tubers and building energy reserves.

If you remove or treat the plant before this stage it stops this tuber formation process. After this stage, this movement of carbohydrates to the tubers slows down or stops. The end result is the herbicide only kills the above ground parts, and doesn’t effect the tubers.

Research carried out at Clemson University found that the sulfonylurea, trifloxysulfuron, to be the best option to control Purple Nutgrass. Several applications gave more than 90% control of Purple Nutgrass in couch³Blanton, R.L., A. G. Estes, L. B. McCarty (2010). Postemergence control of purple nutsedge (Cyperus rotundus) in bermudagrass turf. Proc. South. Weed Sci. Soc. 63:147.

It is likely you will need several applications for complete control, as Purple Nutgrass produces thousands of new tubers a year. Each tuber is viable for three years if there is adequate soil moisture.

If you turn or work the soil, and expose tubers to sunlight before you establish new turf, it significantly reduces the viability of Purple Nutsgrass tubers ⁴Stoller, 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..

Soil and Foliar

There are two post-emergent options for Nutgrass in lawns and turf areas. The first group rely on foliar contact because they don’t have any soil activity, and teh second have both soil and foliar activity.

Foliar Control of Nutgrass.

These include bentazone (trade name: Nutmeg), and glyphosate (trade name: Rapid Fire). Glyphosate is non-selective so will kill any growing plants it touches.

• The success of your spray is depends on what you treat.
• Bentazone works better on Yellow Nutgrass (75% control), than Purple Nutgrass (less than 20% control).
• Glyphosate has better activity on Purple Nutgrass (70%) than on Yellow Nutgrass (55%).

Glyphosate moves through the plant within 3 days, and then kills the foliage and the tuber. ⁵Rao AS, Reddy KN. 1999. Purple Nutsedge and sicklepod response to glyphosate mixtures with ALS-inhibiting herbicides. Weed Technology 13:361- 366..

The key to the control or suppression of Nutgrass in lawns is to make sure that there is good contact between the herbicide and the foliage.

Soil and Foliar.

The second post-emergent group for Nutgrass in lawns and turf are those with soil and foliar activity. These include halosulfuron, which is effective (85% to 95% control) against both Nutgrass species.

Vencill and others⁶Vencill WK, Richburg JS III, Wilcut JW, Hawf LR. 1995. Effect of MON-12037 on Purple and Yellow Nutsedge. Weed Technology 9:148-152. determined that 53 g ai/ha of halosulfuron reduces Purple and Yellow Nutgrass by at least 96% if you apply it to the foliage, the soil, or both the foliage and the soil.

The number of Purple Nutgrass 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 Nutgrass is actively growing. So aim to apply in warm weather and with adequate moisture. Dry conditions will reduce how well they work

Post-emergents for Nutgrass.

1. Prosedge.
2. 3-D.
3. Monument.
4. Nutmeg.
5. The arsenates – MSMA and DSMA

Pro-sedge® (Nutgrass and Mullumbimby couch).

ProForce Prosedge

This is the most common Nutgrass killer and Nutgrass herbicide for with Nutgrass. It is based on the active halosulfuron.

After treatment foliage turns yellow until it totally dessicates. Initial symptoms appear in 7-10 days with full control effects not appearing for 4 to 6 weeks.

• Pros: Cheap; can be used on both cool and warm season turf; low water application volume; low odour.
• Cons: Can develop resistance if overused; need to repeat 4-8 weeks later if you see regrowth; need to add a non-ionic surfactant at 0.25 to 0.5% (v/v).
• Price: $210/500g.

Prosedge Label

Prosedge SDS

Buy Prosedge.

3-D Herbicide (Mullumbimby couch).

3-D herbicide

3D Nutgrass Herbicide is a sedge and Nutgrass killer that also controls broadleaf weeds, and contains Bentazone. This is a great option to manage Nutgrass in lawns if you suspect your Nutgrass herbicide doesn’t work due to resistance issues.

3-D herbicide has a different mode of action compared to everything else on the market.

• Pros: You can use this on both cool and warm season turf; it has a low odour; also controls many broadleaf weeds;
• Cons: It only really works on Yellow Nutgrass; it needs 8 hours to be fully rainfast.
• Price: $320 /10L.

3D herbicide Label

3D herbicide SDS

ProForce Recondo (Mullumbimby couch).

ProForce Recondo Herbicide

This is one of the most common Nutgrass killers and Nutgrass herbicides for dealing with Nutgrass in lawns.

• Pros: A Monument herbicide alternative which also controls numerous broadleaf weeds and cool season grasses.
• Cons: You can only use this safely on couch and zoysia; you need to add a non-ionic surfactant at 0.25% v/v to the spray mixture; a further application is often needed 4 to 8 weeks later if you see any regrowth; it needs 3 hours to be fully rainfast.
• Price: $155/100g

Recondo herbicide Label

Recondo herbicide SDS

Buy Recondo Herbicide.

Nutmeg Herbicide (Nutgrass/Mullumbimby couch).

Quali-Pro Nutmeg

This is a new Nutgrass killer for Nutgrass in lawns, and Nutmeg herbicide contains the active bentazone.

Bentazone is in the benzothiadiazole herbicide group, and inhibits photosynthesis at photosynthesis II. It is a selective, contact herbicide which is absorbed mainly by the foliage, with little translocation.

It works better on Mullimbimby Couch and Yellow Nutgrass, and is less effective on Purple Nutgrass.

• Pros: Excellent resistance rotation option.
• Cons: Need to use a non-ionic surfactant such as Optispread 1000; don’t apply to newly seeded turf; needs 8 hours to be fully rainfast; needs a repeat application 7 to 10 days later.
• Price: $310/5L

Nutmeg herbicide Label

Nutmeg herbicide SDS.

Buy Nutmeg Herbicide.

The Arsenates – MSMA and DSMA.

ProForce Geronimo

MSMA and DSMA have activity on sedges and Nutgrass in lawns, and are foliarly absorbed. They accumulate in the root and leaf tips and then rapidly kill leaf and stem tissue.

MSMA and DSMA have multiple sites of action with a plant, but they are thought to interfere with ATP production (energy storage) and cell division.

You should use these chemicals in hot conditions, as their efficacy is temperature related. Both MSMA and DSMA work better in hot rather than cool weather.
Their temperature requirement means that you shouldn’t use these in cool, cloudy conditions, as they are then unlikely to be effective.

Temperature variations in a 24-hour period do not have much effect on their efficacy however. The arsenicals are absorbed into the plant and their herbicidal effect occurs over time. This means that their efficacy is affected more by the temperature over several hours after spraying, rather than the actual temperature when you spray.

They are both safe on Zoysia at low rates. Do not use on Buffalo.

Geronomo herbicide Label

Geronimo herbicide SDS.

Buy Geronimo Herbicide.

Non Selective Control of Nutgrass.

Many people use Glyphosate on mature Nutgrass plants to try to kill the tubers. Unfortunately, at this stage the herbicide generally doesn’t move very well from the leaves to the tubers, and many of the tubers will be unaffected.

If you want to use Glyphosate to control Nutgrass in lawns you need to apply it when the plants are young, actively growing, and haven’t recently been mowed. If you use Glyphosate, and water quality is an issue then use ProForce Manta Ray.

Ideally, you aim to use Glyphosate, apply it within 4 to 6 weeks of the first shoots emerging. This timing will give the best kill of the plants and their attached tubers, and means that you get control before it reproduces.

ProForce RapidFire Label.

MSDS.

Buy ProForce RapidFire.

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