Grubs in turf: how to effectively manage high pressure infestations

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Marijn Keizers, Wednesday 10 June 2026

164 sec

An integrated approach for greenkeepers and sports field managers

Anyone responsible for managing turf will recognise the symptoms: brown patches that do not respond to irrigation, turf lifting like a carpet, and crows tearing up greens and fairways. The culprit: grubs. These larvae of cockchafers, summer chafers and rose chafers feed unseen on grass roots until the damage suddenly becomes visible. By that stage, a simple solution is often no longer possible.

Secondary damage caused by birds and badgers tearing up turf in search of protein-rich larvae is often even more severe on greens and sports fields than the root feeding itself. This makes a proactive approach essential.

Timing is everything

The success of any control strategy depends entirely on timing. Young larvae in the first and second instar stages (L1/L2) are vulnerable. Once they reach the third instar stage, effective control becomes extremely difficult, whether biological or chemical. The key therefore lies in monitoring adult beetle flights.

Pheromone traps provide a reliable indication of when beetles are flying and laying eggs. The timeline differs by species. Cockchafers typically fly from late April to early June, rose chafers from mid-May through June, and summer chafers from June into late July.

Step 1: prevention and a strong turf surface

A healthy, dense turf surface is the first line of defence. Good drainage and regular aeration promote a healthy root zone that can better withstand damage. Avoid excessive irrigation during the beetle flight period, as beetles prefer moist soils for egg laying. Verticutting, topdressing and overseeding help keep the turf dense and reduce the opportunity for larvae to develop undisturbed.

Step 2: biological control with nematodes

The use of entomopathogenic nematodes is the preferred option for grub control. These microscopic worms actively seek out larvae in the soil, penetrate them and kill them with the help of a symbiotic bacterium. Several conditions must be met for successful application: soil temperatures should be at least 12�C, the soil must remain moist before and for at least two weeks after treatment, and applications should be carried out during cloudy conditions or in the evening because nematodes are sensitive to UV light.

Step 3: Acelepryn under persistently high pressure

A biological approach is not always sufficient. Where populations remain consistently high or unacceptable damage continues over multiple seasons despite nematode applications, Acelepryn may be considered as a targeted preventive addition within an IPM programme.

Acelepryn distinguishes itself through its selective mode of action. The product specifically targets the ryanodine receptors of pest insects and is considered safe for non-target organisms. Birds, mammals, fish and pollinators are not affected. One application per season provides long-lasting protection throughout the vulnerable larval stage. By reducing grub populations, the foraging activity of birds and badgers also decreases, limiting secondary turf damage.

Preventive application: using the right technique

Acelepryn is strictly a preventive product. The active ingredient requires three to four weeks to move through the thatch layer into the root zone. It must therefore be applied before egg hatch; waiting until visible damage occurs is too late. For cockchafers, this means application in May or June, while summer chafers require treatment in June or July.

Application guidelines in brief:
� Rate: 0.6 L/ha
� Keep the soil profile moist after application to keep larvae in the upper soil layer where the product is active
� Maximum of one application per year

When applied correctly, the product reaches the larval zone at the moment young larvae (L1/L2) begin feeding actively. Acelepryn is no longer effective against third-instar larvae, making preventive timing essential.

Legal framework in the Netherlands

Acelepryn is authorised by the Dutch Board for the Authorisation of Plant Protection Products and Biocides (Ctgb) for professional use on lawns, recreational grass areas, sports fields (including golf courses) and turf production. However, authorisation alone is not sufficient. In the Netherlands, chemical plant protection products are generally prohibited on sports fields and golf courses, with only limited exemptions under the Plant Protection Products and Biocides Regulation (Rgb).

The exemptions are strictly defined:
� Cockchafer and summer chafer larvae on sports fields (excluding stadium pitches): permitted
� Cockchafer and summer chafer larvae on golf courses (excluding roughs): permitted
� Leatherjackets on golf greens: permitted
� Other grub species: not permitted on any site

Correct identification of the beetle species is therefore a strict requirement. In addition, use must form part of a documented IPM programme, operators must hold a valid professional certification, and the necessity of treatment must be demonstrable through monitoring results and damage records. Distribution of Acelepryn in the Netherlands is handled exclusively by Vos Capelle.

Conclusion

Effective grub management is built on three pillars: monitoring, timing and identification. Biological control with nematodes remains the preferred option. However, where high populations of cockchafer or summer chafer larvae are clearly established, Acelepryn can provide a selective, effective and preventive addition, provided it is applied before egg hatch and followed by irrigation.

More information is available on the website of Syngenta: (http://www.syngenta.nl/Acelepryn)][www.syngenta.nl/Acelepryn(http://www.syngenta.nl/Acelepryn[/LINK)]

This article was previously published on 3 June 2026 on the Greenkeeper](https://www.greenkeeper.nl/article/54308/engerlingen-in-de-grasmat-zo-pak-je-hoge-druk-effectief-aan]Greenkeeper) website.

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