27 June 2025

Thankyou for Leatherjacket Advice

“Hello Jon – You may remember we sought advice following our leatherjackets infestation! Well, we ordered treatment from you at the end of April, along with some root success treatment and now look at the difference! Pictures of before and after. Close up not 100% yet but really happy! We will be in touch again in the Autumn for the next treatment.  Thank you for your help and advice!” Alison by email

Original Question. “I hope you don’t mind me writing for some advice prior to me purchasing your Leatherjacket Nemasys treatment! Having read the articles on your help and advice page the scenarios are our scenarios! We are in a new development where our garden was turfed two years ago. Year one the lawn was lovely (with lots of starlings visiting which in hindsight means they were after grubs!). Over this wet winter we assumed that heavy rain was washing soil over the garden, and three weeks ago we scarified, removed moss and re-seeded. The seeds are coming through in most places, however we are now thinking that our problem is the more serious one of Leatherjackets grubs! So we just wanted to check that despite it being Spring we can still use the treatment as per the guidance in the screenshot above? We still have more seed left, so should we re-seed again, leave it a few days/weeks or leave it until Autumn?  I also assume that this is something regular that we will then need to do (just annually) in the Autumn? Are we ever likely to get rid of the Leatherjackets i.e. is it possible to break the cycle? I know we must water the lawn beforehand and also after application. Is one water sufficient after application or do we have to do this for several days? I really appreciate your help and can then organise the purchase! Photos attached for info!” Kind regards Alison Palmer

Original Answer – Wow it looks like you have quite an infestation. I cannot be 100% sure just looking ta the damage so can I suggest you lift a piece of turf and check for leatherjackets to be sure. If I was a betting man I would be sure you are going to find lots. The best time to treat leatherjackets is in the autumn, but they will help when applied at double strength at any time of year. Treating now will kill lots and allow you to recover the lawn and then you can “clobber” it in the autumn i.e. treat twice once the daddy long legs have emerged – leatherjackets are the larvae of the daddy longs legs. I am confident the nematodes will work, but you will need to apply at least 3 times this year and if they are in your area it will then become a yearly application to keep them away. If you decide to give it a go I would treat as follows :-

1. Apply Leatherjacket Nematodes at double strength – in your pictures your ground is VERY dry so make sure you pre-water really well as you need these nematodes to soak in a reach the leatherjackets.
2. Feed the lawn with Lawn Food / use a root treatment like Root Success to help the lawn recover.
3. Watch out for daddy long legs emerging in the summer i.e. normally mid-August and then aim to apply nematodes at single strength 2 WEEKS after the mass emergence of the daddy long legs.
4. Then repeat the nematode treatment 3 weeks later to kill any later emerging daddy long legs / crane flies.
5. Give your lawn a final feed with a low nitrogen Autumn Lawn Feed to encourage root growth.
6. Add a autumn treatment of Leatherjacket Nematodes (applied in late Sept) to your normal lawn care routine to keep them away.

As for watering – it depends on the weather. The aim is to stop the nematodes drying out for 2 weeks without washing them away, so if the weather is really hot and dry then watering a few times will be necessary but if it rains or is dull then you may only need to water once of twice. I hope this helps. Kind regards Jon @ Green Gardener

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