Leatherjackets are crane fly larvae that chew through grass roots all autumn and winter, leaving you with soft, spongy turf that pulls up like carpet and birds tearing holes in it looking for a meal. This guide covers the exact window to treat lawn leatherjackets, what to buy, and how to stop them coming back in 2026.
- Confirm lawn leatherjackets with a soapy water flush before treating anything.
- Apply Steinernema feltiae nematodes in September while soil is still above 12°C - Buy this window, not spring.
- Water nematodes in immediately and keep soil moist for 14 days or the treatment fails.
- Chlorpyrifos has been banned in the UK since 2016, so nematodes are the only reliable control left.
- Overseed and feed damaged patches in April 2026 once larvae numbers have dropped.
Why this matters
A leatherjacket infestation doesn't just thin your grass - it invites secondary damage that's often worse than the pest itself. Starlings, crows and foxes rip up turf hunting the grubs, and a lawn that looked fine in November can be shredded by February.
Numbers matter here because timing is everything. Leatherjackets hatch from crane fly eggs laid in August, feed through autumn and winter, then do their heaviest root damage in early spring before pupating in May. Miss the September-October treatment window and you're stuck watching the damage happen with no chemical fallback, because chlorpyrifos-based products were withdrawn from UK garden use in 2016. Nematode treatment is now the only control that works, and it only works within a narrow soil-temperature range.
Homeowners across the UK dealing with lawn leatherjackets tend to make one of two mistakes: treating too late (December, when soil is too cold for nematodes to move) or not treating at all and reseeding bare patches that just get eaten again next autumn.
What you'll need
- A soil thermometer or a general sense of the season - nematodes need soil above 12°C
- Biological washing-up liquid (not standard detergent) for the flood test
- A watering can or hose-end sprayer for application
- Steinernema feltiae nematode pack, sized to your lawn area in square metres
- A garden fork or hollow-tine aerator for post-treatment recovery
- Grass seed and a balanced autumn feed for overseeding damaged patches
- A rake or lawn scarifier if thatch is present
Step 1: Confirm you actually have leatherjackets
Don't guess - other issues like drought stress, chafer grubs or fungal disease cause similar brown patching. Mix 30ml of biological washing-up liquid into 4 litres of water and pour it over a 1m² section of the affected area at dusk.
Within 10 minutes, leatherjackets irritated by the soap solution surface and you can count them. More than 25 per square metre in autumn is generally accepted as the threshold where treatment pays off; below that, the lawn usually recovers on its own. Common mistake: testing only one patch and assuming the whole lawn is clear - test at least 3 spots across the garden.
Step 2: Time the treatment to early autumn
September is the window that works. Soil needs to be consistently above 12°C for Steinernema feltiae nematodes to move through it and find larvae, and young leatherjackets in early autumn are more vulnerable than the larger, hardier grubs you'll find by December.
Treating in spring is possible but far less effective, because by March the larvae are bigger, tougher, and close to pupating - most of the root damage is already done. Common mistake: waiting until visible damage appears in January, by which point the September window has closed for another year.
Step 3: Apply the nematode treatment
Mix the nematode pack into water following the pack's dilution rate (this varies by product size and lawn area, so check the label rather than guessing) and apply with a watering can or hose-end sprayer in the early evening when UV light won't kill the microscopic nematodes.
Cover the full lawn evenly, not just the damaged patches - leatherjackets migrate, and untreated zones become a reservoir for reinfestation. Common mistake: applying in direct midday sun, which kills a large percentage of nematodes before they reach the soil.
Step 4: Water in immediately and keep the soil moist
Irrigate straight after application to wash nematodes off the grass blades and down into the root zone where the larvae live. Then keep the lawn moist for the following 14 days - light watering every 2-3 days if there's no rain.
Nematodes die in dry soil before they get the chance to infect anything, which is the single biggest reason this treatment underperforms. Common mistake: treating right before a dry spell and not following up with irrigation.
Step 5: Recheck numbers after 2-3 weeks
Run the soap flood test again in the same spots you tested originally. A drop from 25+ per square metre down to single figures means the treatment worked; if counts are still high, a second application later in September is worth doing while soil temperature still allows it.
Common mistake: assuming one treatment is permanent - reinfestation from neighbouring gardens and fresh crane fly egg-laying happens every August.
Step 6: Repair the damage
Once larvae numbers are down, rake out dead grass, spike compacted areas with a garden fork or hollow-tine aerator to improve root growth, then overseed bare patches and apply an autumn feed. Spring 2026 recovery is faster on lawns that get this aftercare in October rather than left bare over winter.
Common mistake: overseeding immediately after nematode application - give it the full 14-day watering window first so new grass isn't disturbed.
Step 7: Deter birds while the lawn recovers
Birds dig for leatherjackets whether or not you've treated, and a lawn mid-recovery is an easy target. Bird-scare tape, netting over the worst patches, or simply increasing foot traffic in the garden during peak feeding hours (early morning) reduces the tearing.
Common mistake: blaming bird damage on the treatment failing, when it's actually a sign the larvae were there and the birds found them before or during die-off.
Get a professional lawn leatherjacket treatment
Lawnscience treats leatherjackets and repairs the damage they leave behind.
Troubleshooting
- Nematodes applied but larvae counts didn't drop: soil was likely below 12°C or too dry post-application - retest soil temperature and reapply once conditions improve, ideally before mid-October.
- Bare patches keep spreading even after treatment: this is often existing damage from feeding that already happened, not active larvae - overseed and feed rather than treating again.
- Birds are digging up newly seeded areas: cover with lightweight netting for 3-4 weeks until seed establishes.
- Lawn was treated in spring with no visible improvement: spring treatment targets larvae close to pupation - expect a partial result and plan a proper September 2026 application instead.
- Reinfestation every single year: neighbouring untreated gardens and open borders are common sources - there's no way to fully prevent crane flies laying eggs, only to manage larvae numbers annually.
- Unsure if it's leatherjackets or chafer grubs: leatherjackets are legless and grey-brown; chafer grubs are C-shaped with visible legs and a distinct head - the soap flood test brings both to the surface for a clear look.
Tools and resources
- Biological washing-up liquid for diagnostic flood testing
- Steinernema feltiae nematode packs, sized by lawn area
- Soil thermometer to confirm the 12°C application threshold
- Hollow-tine aerator or garden fork for autumn recovery work
- Autumn lawn feed and overseeding mix for damaged patches
- Professional treatment through Lawnscience if diagnosis, timing or application isn't something you want to manage yourself
What to do next
If the soap flood test comes back high and you're not confident mixing and timing a nematode application correctly, get it treated professionally before the September 2026 window closes - a missed window means waiting a full year for the next reliable chance at control.
FAQ
What are leatherjackets in a lawn?
Leatherjackets are the larvae of crane flies (daddy long-legs), grey-brown and legless, that feed on grass roots through autumn and winter. Heavy infestations cause soft, spongy turf and attract birds digging for a meal.
When is the best time to treat lawn leatherjackets?
September is the best time, while soil temperature is still above 12°C and the larvae are young. Waiting until winter means colder soil stops nematode treatment working properly.
Are there chemical treatments for leatherjackets?
No effective chemical treatment is available in the UK - chlorpyrifos, the previous standard control, was banned for garden use in 2016. Steinernema feltiae nematodes are now the main treatment option.
Do nematodes for leatherjackets harm pets?
Steinernema feltiae nematodes are a biological control that's safe around pets and children once watered into the soil. They only target soil-dwelling insect larvae, not mammals.
How long does nematode treatment take to work?
Expect results within 2-3 weeks of application, provided the soil stays moist throughout that period. A follow-up soap flood test confirms whether larvae numbers have dropped.
Can I treat leatherjackets in spring instead of autumn?
Spring treatment is possible but less effective, because larvae are larger and closer to pupating by March. September treatment targets them while they're smaller and more vulnerable.
Why do birds dig up my lawn even after treatment?
Birds are drawn to larvae already present in the soil, and some digging can continue during the die-off period. Netting or bird-scare tape over the worst patches protects the lawn while recovery finishes.
How do I know if it's leatherjackets and not another lawn pest?
A soapy water flood test brings leatherjackets to the surface within 10 minutes for a clear count. More than 25 per square metre in autumn is generally the threshold where treatment is worth doing.
One last thing
The soap flood test costs nothing and takes 10 minutes, yet most lawns get treated for leatherjackets based on guesswork from brown patches alone - test first, because drought stress and chafer grubs look almost identical from a distance and neither responds to nematode treatment.