Hi @janaki,
A warm welcome to the Bunnings Workshop community and thank you for your question.
When you are applying the neem oil to the soil, are you ensuring you fully soak the entirety of the soil? Or are you just watering a bit at the top of the pot?
For neem oil to be effective in the soil, you need to ensure you are mixing it to the required ratio and soaking the entirety of the soil with this mix, so the grubs have nowhere to hide.
With OCP 250ml Eco-Neem Concentrate Botanical Insecticide, for example, you would mix 30mL into 10L of water. You would then apply 1L of this mixture for every 8L of soil.
If you haven't already done this, then it would be worth another try with the neem oil as this is the best way to kill any grubs that have found their way into the soil.
Replacing the soil will also be beneficial, but if the grubs have found their way in the past, they will likely be able to again. Unfortunately, this would mean replacing the soil in all of your pots and disposing of the old soil. If you need to do this, then make sure you inspect the root ball when transplanting as the grubs can be hidden. If they are transplanted alongside the plant, the infestation will just start all over again.
If you try the neem oil again and have no luck, unfortunately, this may be the best option.
Allow me to tag @Noelle and @mich1972 for their thoughts.
Let me know if you have any further questions.
Jacob
