Argentine Stem Weevil in Turfgrass

The Argentine Stem Weevil (Listronotus bonariensis) is one of the most destructive turf pests in temperate Australia. The larvae cause the most turf damage. They attack ryegrass, bent, and fescue, and reduce turf density and its playability. With multiple lifecycles in a season timing of any control measures is critical.

As a result, integrated programs that combine monitoring, and cultural, biological, and chemical controls are essential to manage this pest.

How To Identify Argentine Stem Weevil (ASW).

Adults. These are small (around 3 mm long) grey to brown weevils with a short snout and a mottled body.
Argentine Stem Weevil Larvae. The lavae are cream to white, have no legs and a tan head capsule. You often find these inside grass tillers.
Symptoms. The first signs of damage are small yellow or straw coloured patches. As damage becomes more evident it shows as tiller collapse, poor surface recovery, and the turf can be easily pulled up by hand.
Key indicator. The main indicator of ASW damage is the presence of “dead-heart” tillers. You can pull these out easily, and they show signs of tunneling damage.

Life Cycle of Argentine Stem Weevil.

In Australia there can be two to three overlapping generations per year.
Weevil activity begins once the mean daily temperatures exceed around 10 °C.
Weevils lay their eggs in tiller sheaths and these then hatch 9 to 30 days later.
Argentine Stem Weevil larvae feed inside tillers for 2 to 8 weeks before they then move into the soil.
Once in the soil the larvae form pupae in small soil cells that are around 5 mm deep in the soil.
Adults then emerge, feed briefly, and lay eggs. This perpetuates cycles through the Spring, Summer, and early Autumn.
Most damage occurs when the larvae feed.

argentine stem weevil lifecycle in Australian turf conditions.

Monitoring and Risk Indicators.

Inspect turf from early in the Spring. Focus on areas with a history of ASW infestation.
Conduct soap-flush counts and dissect tillers weekly during peak risk periods.
Use Growing Degree Days (GDD) with a 10 °C base temperature. It takes approximately 450 GDD for ASW to go from an egg to an adult. Our Argentine Stem weevil Predictor helps make things easier with this.

Stem Weevil Counts.

You can use Pyrethrum to flush the Argentine stem weevil out of the turf to get a better idea of the population pressure.

Visual inspection: Take 10 × 10 cm turf plugs, and record the number of larvae per plug.
Flotation test: Add 10 ml of detergent to 10 L of water. Drench 0.1 m² of turf with this.
Thresholds: If you see >15 larvae per plug then this should be a trigger to start treatment.

Another option is to use Pyrethrum. This applied a weak dose of insecticide that irritates the weevils and brings them to the surface where you can count them.

Prepare the solution: Mix 20 mL of Pyrethrum (or another fast-acting contact insecticide) with 5 litres of water in a watering can.
Apply to the turf: Evenly drench 1 litre of the mixture over 0.25 m² of turf (a 0.5 m × 0.5 m area). Repeat the application on a nearby comparison area for consistency.
Observe and record: Watch both treated areas closely for at least 10 minutes. Adult weevils will emerge from the thatch and surface as they are irritated by the solution.
Count and calculate: Collect or count the surfaced adults. Multiply your count by 4 to estimate the number of weevils per square metre.

The VGCSA (Ford et al, 2000) suggest the following action threshold (AT) based on grass type. The AT for Poa annua greens is around 3 adults m², particularly if hot weather is forecast. The number for bent greens is around 7 adults m².

Control Options for Argentine Stem Weevil.

Active	Brand	Rate per Ha	Target Stage	REP	IRAC Group	Price / Ha	Water L/Ha	Longevity
Spinosad 120 g/L	ProForce Curatol 120 SC	4 L	Adults + Larvae	Once Dried	5A	$600	400 to 800	4 weeks
Chlorantraniliprole 200 g/L	Acelepryn	0.75 to 1.5 L	Larvae	See label	28	$517 to 689	400 to 600	Up to 6 months
Cyantraniliprole 200 g/Kg and Thiamethoxam 200 g/Kg	Spinner	1 Kg	Larvae	See label	4A + 28	$639	300 to 500	4 to 6 weeks
Tetraniliprole 42.8 g/L	Tetrino	1.15 to 2.3 L	Adults + early Larvae	See label	28	$225 to 472	400	6 to 8 weeks
Indoxacarb 320 g/L + Novaluron 80g/L	Twister	3 L	Eggs, Larvae + Adults	Once Dried	15 + 22A	$1155	400	4 to 6 weeks
Fipronil 100 g/L	Termiforce 100SC	0.75 L	Larvae and Adults	Once Dried	2B	$143	400	Up to 4 weeks
Bifenthrin 100 g/L	Rumbler 100SC	1.2 to 2.4 L	Adults	See label	3A	$36 to 72	200 or more	2 weeks
Entomopathogenic nematodes	Nemastar	2.5 × 10⁹	Larvae	See Label				10 Days

Cultural and Biological Control of Argentine Stem Weevil.

Cultural.

Maintain optimal tissue N levels and irrigate to help turf recovery.
Core-aerate any compact areas to improve oxygen and root penetration into the soil profile.
Dethatch in the Spring to reduce the available habitat for Argentine Stem weevil larvae.
Do not mow below the recommended height of cut. Scalped turf encourages egg laying.

Cultural Practices Table.

Practice	Benefit	Limitation	Timing
Roll greens after irrigation	Crushes pupal chambers	Minimal if soil dry	Late Spring
Light sand topdressing	Disrupts egg laying	Excess can dull mower	Jul to Aug
Maintain N levels	Promotes recovery	High N favours larvae	Year round

Biological.

Entomopathogenic Nematodes (EPNs) are beneficial nematodes that infect stem weevil and kill them via symbiotic bacteria.

Pros of EPN’s vs ASW.

They reduce chemical use. EPNs are effective biological alternatives to chemicals.
EPN’s target Argentine Stem Weevil larvae in the soil and thatch. Trials report around 90 % control of larvae after 14 days (Ford et al., 2000).
EPN’s are compatible with IPM. They complement cultural practices like mowing, irrigation, and pest monitoring.
They reduce any resistance risk.
Environmentally safe. They are non-toxic to plants, vertebrates and many non-target organisms.
Long-term suppression. Recent research shows EPNs persist and reduce turf insect pests over several years (though not ASW specifically).

Cons / Limitations.

Variable can give results.
Very dependant on the use environment. Soil temperature, moisture, UV exposure, soil structure, thatch depth, and the microbial population all affect EPNs. For example, the you need to use these when soil temperatures exceed 15 °C.
Time sensitive. You must use these on the susceptible larval stage. ASW has multiple generations, so poor timing can lead to poor results.
Cost and logistics. Large areas of turf (greens, collars, tees) may require high densities of EPNs, boom spray equipment, and careful handling (storage).
Persistence. While long-term suppression is possible, many commercial strains may have lost their persistence traits after mass-production.
Complementary rather than standalone treatments. Some turf managers report better results when they combine EPNs with chemical controls rather than aiming to replace chemicals entirely.

How to Get the Best Results.

1. Target the Right Stage.

Use degree day models to better target generations. ASW can have 3 to 4 generations per year in Australia from the Spring to the Summer.

2. Use at the Right Time.

Moisture. Make sure to irrigate the turf before and after you use these. This helps them move into the target zone and then survive.
Temperature. For optimal activity the soil temperature needs to be above 15 °C.
Thatch depth. Heavy thatch reduces nematode penetration or movement. If you reduce the thatch levels it improves their efficacy.
Water them in after use. Lightly water to move the nematodes off the leaf-sheath into the soil and thatch zone. Avoid heavy irrigation rates as these can tend to wash them away.
Use in low UV and low heat periods (e.g., late afternoon or early morning) to reduce nematode stress or desiccation.

3. Use the Right Rates and Coverage.

Make sure you evenly apply your spray. Use the right equipment, and cover the entire target area.
Ensure good product distribution. Turf collars and greens are sensitive areas.

4. Integrate with Cultural and Chemical controls.

Combine with mowing, and appropriate fertiliser regimes. Avoid excessive N just before any expected weevil egg-laying, as lush growth tends to attract adults.
Apply chemical larvicides or adulticides earlier or along with EPNs to knockdown the adult population. The nematodes will give better results with low population densities. Turf managers tend to see the best results when they use EPNs in conjunction with chemical controls.
Monitor pest numbers so you can gauge how effective the EPNs are and decide whether you need to re-apply.

5. Follow-up.

ASW has multiple generations in a year and the turf environment is dynamic. This means that you may need to make repeat treatments.
Focus on areas with a history of ASW.

6. Manage expectations.

EPNs may not eliminate all the larvae. So don’t expect to get 100 % control after one application.
Be aware that if the turf is under stress from heat, drought or compaction you can still see damage.

Management Protocol.

Pre-Season (Late Winter to Early Spring)

Review historical ASW hotspots.
Begin to track GDD.
Lightly dethatch or groom turf areas to remove winter litter.

Early Season (Start of Spring).

Inspect for over wintered adults. Use an adulticide (e.g. bifenthrin or spinosad) once the GDD are ≥ 80.
Avoid excessive irrigation or N.

Mid-Season (Larvae).

Monitor the GDD. The mid larvae stage of Argentine Stem Weevil corresponds to 270 to 300 GDD.
Use a systemic larvicide (e.g. chlorantraniliprole or tetraniliprole).
Now is the time to use nematodes.

Late Season (Adult Emergence / New Generation).

At ~450 GDD, expect adults to emerge.
Rotate chemical groups.
Combine with aeration and cultural programs.

ASW Program Notes

SPINNER is very systemic. It controls early stage Argentine stem weevil larvae (First and Second instar) inside plants.

Start to monitor for adult numbers as early as July on hot spot areas. When numbers increase, start the first TERMIFORCE application to control migrating adults. 7 to 14 days later use SPINNER for early stage larvae, then CURATOL 14 days later.

Peak migration timing from surrounds onto greens depends on the weather conditions. When you find large numbers of adults on greens, treat the surrounds with an adulticide to reduce migrating populations.

Confirm synthetic pyrethroid (SP) efficacy early in the season as resistance will reduce control. TERMIFORCE use may help with ASW control.

There is anecdotal ASW resistance to SP's such as Bifenthrin in Australia. Resistance is seen to SP in USA on the Annual Bluegrass Weevil (ABW), a close relative with similar management strategies.

If you suspect SP resistance, swap CURATOL for one or more surround treatments. Check SP effectiveness by flushing for numbers on green edges before and after use.

Environmental conditions impact any program. Monitor populations and environmental changes over the year and adapt accordingly.

⚠️ Read all label directions. Rotate MOA groups. Align each spray to the lifecycle band.

Resistance and Chemical Rotation.

The key to resistance management is to alternate between Groups 28, 5A , and 22A.
Limit any single mode of action to once per generation.
Include a biological or cultural control in every alternate generation.

Resistance Management.

Its important to target the right stage with the right chemical. The two tables below can help with this.

Table Showing Chemical Group, Mode of Action and Resistance Risk for ASW Insecticides.

Chemical Group	Example	Mode of Action (MOA)	Resistance Risk	Notes
3A (Pyrethroids)	Bifenthrin	Sodium channel modulator	High	Use on early adult stages only
5A (Spinosyns)	Spinosad	Nicotinic acetylcholine receptor activator	Moderate	Good rotation option for adults + larvae
22A (Oxadiazines)	Indoxacarb	Voltage-dependent Na⁺ channel blocker	Moderate	Avoid consecutive applications
28 (Diamides)	Chlorantraniliprole, Tetraniliprole	Ryanodine receptor modulator	Low	Ideal product for larval stages

Best Practice: Rotate across IRAC groups between generations. Avoid repeat use of pyrethroids due to the likelyhood of cross-resistance. Combine actives (spinosad / diamides) with biologicals to slow the onset of resistance.

Table of a Suggested Rotation Schedule.

Generation	Dominant Stage	Preferred MOA	Alternate MOA
1	Adults	3A (Pyrethroid)	2C (Fipronil)
2	Larvae	4A (Spinosad)	28 (Cyantraniliprole)
3	Pupae to Adult	5A (Indoxacarb)	Biological (EPNs)

Table of Chemical vs Cultural Controls For Argentine Stem Weevil.

Control Type	Pros	Cons	Timing	Best-Use Scenario
Chemical (e.g. Acelepryn, Tetrino, Curatol)	High efficacy, predictable, fast results	Cost, potential resistance, regulatory limits	Peak larval or adult stage	Active infestations or high-value sports turf
Biological (nematodes)	Low resistance pressure, safe for environment	Needs moisture, short persistence	Mid-larval phase	Sites limiting chemical input or near water bodies
Cultural (e.g. aeration, dethatch, good nutrition)	Improves resilience, no residue	Labour intensive, indirect	Year-round	Baseline strategy for all sites
Rotation	Balanced approach, resistance control	Requires detailed tracking	Continuous	Long-term program across multiple generations

Summary

To manage Argentine Stem Weevil in Australia it needs precision timing, and data-driven monitoring. You can best achieve this if you integrate cultural programs, and use biologicals in conjunction with modern selective chemistry.

Adopting rotation programs that include the new formulation of Spinosad ensures good resistance management and long-term field results.

References

Barratt B.I.P. et al. (2016). Is the invasive species Listronotus bonariensis (Kuschel) a threat to New Zealand natural grasslands? Front Plant Sci. PMC 4960262.
Envu Australia. Technical Notes: Argentine Stem Weevil.
Ford P. et al. (2000). Argentine Stem Weevil Control using Entomopathogenic Nematodes.
King, P.D. & Kerr, R. (1985). “The development and biology of the Argentine stem weevil (Listronotus bonariensis Kuschel) (Coleoptera: Curculionidae) in Australia.” Australian Journal of Entomology, Vol. 24, pp. 123–130.
Marshall, D.B. (2017). “Population dynamics and control strategies of the Argentine stem weevil in New Zealand turf and pasture systems.” New Zealand Plant Protection, Vol. 70, pp. 135–142.
NuTurf. Successful Approaches to Managing Stem Weevil.
Envu Australia. Argentine Stem Weevil Identification & Control.
Vittum, P.J. (2019). “Chemical and biological control trials of weevil pests in turfgrass: Proceedings of the 2019 Rutgers Turfgrass Research Conference.” In: Proceedings of the Rutgers Turfgrass Research Conference, New Brunswick, NJ; pp. 45–58 (2019).

FAQ

What are the risks of ignoring ASW or delaying treatment?

Failure to act early if there is an Argentine Stem Weevil infestation can result in rapid turf loss, particularly in perennial ryegrass and Poa annua surfaces. Root and tiller destruction leads to the turf thinning out, poor playability, and the surface becoming unstable underfoot.

If there are severe infestations it may require a full turf renovation, which will lead to a significant increase in costs. A delay in response also allows populations to buildup across overlapping generations, which makes control progressively harder and more expensive.

How do I select chemical insecticides for ASW and manage resistance?

You should target adults early with fast-acting contacts and control larvae with systemic or ingestion products. Aim to rotate between IRAC Mode of Action groups to delay any resistance development:

Group 2B (phenylpyrazoles). This group includes fipronil which is excellent on migrating adults and Argentine Stem Weevil larvae. This is good for perimeter or surround applications.
Group 3A (pyrethroids). This group includes bifenthrin which provides a rapid adult knockdown. You need to make sure that this group has no resistnace issues as resistance is documented in Australia and in related species overseas.
Group 5A (spinosyns). This includes a new turf registered product for Australia – spinosad. Spinosad is derived from soil bacteria, and works on both adults and larvae through ingestion. It is excellent rotation anchor when you suspect pyrethroid resistance.
Group 28 (diamides) include chlorantraniliprole. Cyantraniliprole provides long term residual suppression of Argentine Stem Weevil larvae. It is also highly systemic for early instars that are inside tillers.
Group 4A + 28 combinations such as thiamethoxam + cyantraniliprole offer systemic control of feeding larvae.
Group 22A (oxadiazines). Indoxacarb.

Resistance management: Verify synthetic pyrethroid (SP) effectiveness by flushing for population counts before and after use. If you suspect resistance, substitute Group 5A or Group 2B for surround treatments. Avoid repeat use of any one group within a generation.

Always check APVMA label approvals, follow withholding periods and re-entry intervals, and time applications to actively feeding stages using degree-day monitoring for maximum efficacy.

What cultural practices help reduce ASW risk?

Frequent aeration and sand top-dressing will improve soil oxygen levels and reduce thatch. Both of these practices will make conditions less favourable for egg laying. Balanced fertiliser programs help maintain turf vigour and aid recovery. Avoid excessive N in the summer, as this just encourages soft, lush growth which is preferred by larvae.

Maintain appropriate mowing height to reduce stress, and manage any irrigation to avoid extended dry periods that weaken turf and amplify feeding symptoms.

When is the monitoring window for ASW in Australia?

In south east Australia, activity begins in the late Winter to early Spring as temperatures exceed 10 °C. It then continues through the Summer into the Autumn. Overwintered adults resume activity and begin to lay eggs from August to October, with larvae being most active from September through to March.

Development follows a base 10 °C degree-day model, with approximately 480-485 GDD being required per generation. This allows two to three overlapping generations per season. You should start monitoring in the late Winter (July-August) and continue this fortnightly until the late Autumn.”

What are the early warning signs of ASW damage?

The first sign is the turf has a patchy discolouration or a dull, water-stressed appearance even if there is adequate irrigation. As the larvae continue to bore into the stems, affected tillers show dead-heart symptoms. This means that the central shoot easily pulls free, to expose a hollow stem with the larvae inside.

The damaged turf feels spongy underfoot and can be easily peeled back. This differs from disease or drought symptoms, which usually affect the leaves more uniformly rather than the individual tillers. On close inspection, the presence of small cream-white larvae with tan heads will confirm an infestation. Small grey-brown adult weevils (~3mm) may be visible on the surface during the early morning or after soap flushing.

What turfgrass species are most vulnerable to ASW?

Argentine stem weevil (Listronotus bonariensis) primarily targets perennial ryegrass, Winter Grass (Poa annua) and bentgrass species. It also attacks annual ryegrass and occasionally fescues under stress. In Australia, sand-based, intensively managed ryegrass sports fields and golf greens are at highest risk, especially where ryegrass dominates over couch or kikuyu. Warm-season grasses such as couch and kikuyu are less preferred hosts but may suffer incidental feeding during peak pressure.

The host preference is: Perennial ryegrass ≈ Poa annua > Annual ryegrass > Bentgrass > Fine fescues > Tall fescue >> Warm-season grasses