6 July 2026

Treating a serious Leatherjacket infestation that is ruining the lawn.

Q. “We have a serious infestation of leatherjackets and I have enclosed pictures from before and after. We have currently and have so far treated the lawn with nematodes at double strength. The lawn has been both cut and aerated. I was intending to give it another couple of treatments with nematodes over the next few weeks but would welcome any advice as to what else to do to try and save it, including ideas in a timeline please? I have read your online advice but I’m feeling slightly muddled as to what order to carry these things out. I also wondered whether it would just be easier to start again with the lawn as it looks so unsightly. Would you also suggest over seeding it at any point or is it best to leave it until all of the treatments are applied please? Many thanks!” Sandra

A. Thanks for the message and certainly looks like leatherjacket damage, but can I just check that you have actually seen the pest i.e. if you lift some turf do you find active leatherjackets or are they crawling out when it rains onto the paving slabs? Just want to check the pest has been correctly identified? Assuming it is then as you suggest multiple applications is a great way of getting on top of the problem, but I would leave a longer time between applications i.e. application at 4 or 6 weekly intervals until they pupate is ideal. Once they pupate in August i.e. the daddy long legs emerge you can stop treating for 2 weeks and then the best time to treat is 2 weeks after the mass emergence of daddy long legs which is normally mid September.

Reply “Yes they are leatherjackets as we have found a few of them whilst treating it. Is there anything else we should treat the lawn with ahead of the emergence of the daddy long legs in the autumn at all, or is it just a case of leaving it as it is until then please? Would you continue to treat the lawn with nematodes also at 4-6 week intervals until then?” from Sandra

A. Thanks for confirming and the best time to treat leatherjackets is in the autumn, but the nematodes will help when applied at double strength at any time of year. By treating now with Nemasys Leatherjacket Killer  you will kill lots and this will allow you to recover the lawn and then you can “clobber” it in the autumn i.e. treat once the daddy long legs have emerged and then again just before temperatures drop. I am confident the nematodes will work, but you will need to apply at least twice 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 another lot of Leatherjacket Nematodes NOW at double strength.
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 Nemasys Leatherjacket nematodes at single strength 2 WEEKS after the mass emergence of the daddy long legs.
4. You can repeat the autumn nematode treatment 6 weeks later to kill any later emerging daddy long legs / crane flies to make sure you get them all.
5. Give your lawn a final feed with a low nitrogen Autumn Lawn Feed between Sept – Feb 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.

I hope this helps Jon @ Green Gardener

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