When to Use Crane Fly Larvae Treatment (Leatherjacket Control Guide)

A Leatherjacket (larvae) is the child of the Crane Fly or Daddy Longlegs. These larvae are the real culprits when it comes to lawn damage, munching on the delicate white roots of grass and leaving your lawn looking tired and patchy. They're also a favourite snack for birds like crows, magpies and starlings, which can leave behind unsightly holes as they peck through your turf looking for them. These pests are often referred to as leather jacket bugs, especially by homeowners trying to identify the cause of lawn damage.

Most lawns will have a few leatherjackets without issue, but if they appear in large numbers, it's time to take action. In this guide, we'll explain what leatherjackets are, how to identify a problem, when to use crane fly larvae treatment, and how to repair your lawn afterwards.

Found in the soil of lawns, leatherjackets – commonly known as leather jacket bugs – are grey, tubular grubs up to 3cm long, with tough, leathery skin (hence the name). The first signs of an infestation usually aren't the grubs themselves, but the yellow or brown patches that develop as a result of them eating grass roots. If you suspect leatherjackets, peel back a small piece of turf, if you find several grubs per square foot, then your lawn may be at risk.

Even though having a few of these creatures in your lawn is no cause for concern, it can come to a point where it becomes a problem. A way of knowing is when lots of adult Crane Flies can be seen from around late July to September; this is a good indication that it will be an issue in your lawn the following year. Another indication is lawn damage by the wildlife, birds will start sweeping down in search for them pecking at the lawn ripping grass and thatch out.

A few won't usually harm your lawn, but large numbers can cause visible damage:

• In lawns: Grass turns yellow or brown, thins out, and in severe cases dies back completely.
• In flower beds or plots: Seedlings and young plants can be killed if their stems are damaged.
• By birds and wildlife: Crows, rooks, and starlings dig into lawns to eat the grubs, creating messy holes and pulling up turf.

The best time to treat leatherjackets is when the larvae are small and most vulnerable. Crane flies lay their eggs in August, and the larvae hatch shortly after.

• Time to act: March to October. 
• Late summer to autumn (August–October): The larvae are young and closest to the soil surface, making treatments most effective.
• Spring (March–May): A second opportunity, as the larvae feed again before pupating into adults. 

Applying treatment outside these periods is less effective because the grubs are either too deep in the soil or have already pupated.

The only effective option available today is a beneficial nematode treatment, such as Nemasys J. Chemical pesticides for leatherjackets are no longer available in the UK, so nematodes are now the best natural method of control.

Damaging leatherjacket larvae are laid as eggs in lawns during August by the Crane Fly. Once applied, nematodes (which are microscopic organisms) seek out and infect the grubs. They stop the larvae from feeding within 3 days, and most die within 10-14 days. The nematodes then complete their life cycle within the larvae before moving back into the soil to search for more hosts, meaning pest control continues naturally.

These beneficial parasitic nematodes are extremely effective when used correctly and can be applied by professionals, or at home if you follow the instructions carefully. If you are considering applying them yourself, it's important to remember:

• They must be applied at the correct time during the grub development stage.
• The soil needs to be moist.
• Temperatures must be suitable for nematode survival.
• They must be stored correctly before use.
• If they cannot find the grubs, they will die and the treatment will not work. 

For best results, nematodes should be applied when the leatherjacket larvae are small and close to the soil surface, usually in late summer to early autumn, or again in spring. This makes them the most effective choice when you need crane fly larvae treatment.

Once the leatherjackets are under control, you may still be left with patches of damaged grass. The recovery process depends on how badly the roots have been eaten. 

• Light damage: A boost with our A1 Lawn Ultimate Spring Summer Lawn Fertiliser will encourage new root growth and revive the grass. 
• Severe damage: Reseeding may be necessary. Scarify the damaged area, rake level, sow new seed, and top dress lightly to protect from birds.

For even stronger results, apply our A1 Lawn New Grass Pre-Seed Fertiliser 2-4 weeks after germination to help roots establish quickly.

Keep newly seeded areas moist for 4-6 weeks. If rainfall is lacking, our A1 Lawn Ultimate Lawn Seaweed Extract is a great boost for keeping your lawn wet, plus it is an excellent source of plant nutrients and organic carbon, promoting strong and vigorous growth.