15 April 2025

Will Leatherjacket Nematodes work?

Q. “Hello, would you mind me asking for your advice please, regarding the issue of leatherjackets. We unfortunately have found them in both our front and back lawns. However, whilst we think the back lawn can be saved, we are not sure if Nematodes will work in our front lawn as it appears to be infested. I will attach some photos and would really appreciate your advice. We have been considering digging up the lawn and once the top 6” or so has been removed, treat the soil with nematodes to hopefully kill any remaining leatherjackets. Then reseed once we know they have all been destroyed. However, this will obviously be costly! I am just not convinced that the nematodes will kill this amount off (at their current size), even with double the dose?” Niki by email

A. Thanks for the message and wow that is quite an infestation and will take some shifting, but nematodes do work. The best time to treat leatherjackets is in the autumn, but they will help when applied at double strength at any time of year. Although the front lawn is heavily infested, 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 Nemasys 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 Fertiliser / 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 nematodes.
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.

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