Do I apply neem oil on top of mulch or directly on soil for curl grub infestation?

[KimF]

Hi I have discovered lots of curl grubs in a large garden bed in the backyard. It’s planted with natives that have started struggling (one died) and I discovered the grubs when I went to replace the dead banksia with new plants. There are so many- about 5 per shovel of dirt! 
I bought Neem oil to treat.. but I’ve recently laid around 8cm of wood chip mulch on the bed - do I need to move the mulch and treat the whole bed with neem oil? 

[MitchellMc]

Welcome to the Bunnings Workshop community @KimF. It's sensational to have you join us, and many thanks for your question about applying neem oil.

Ideally it would be best to apply directly to the soil, but you can apply over the mulch. Obviously, some of your solution will be absorbed by the mulch, so you'd need to account for that and make sure the soil becomes saturated after it passes through the mulch. Just give the area a good drenching with a watering can.

Please let me know if you have any questions.

Mitchell
 

[felladeb]

I also have curl grub in my garden bed (heavy clay) & at least 2 native trees are dead or dying. It’s mid May & I’m in western Victoria. Is there a better time to treat curl grub (I’ve tried water with dish detergent to flush to surface. No success. Is Neem oil successful or do I need something stronger and when to apply? Now? Or wait til they’re in they’re cycle ie: Spring?

[MitchellMc]

Welcome to the Bunnings Workshop community @felladeb. It's brilliant to have you join us, and many thanks for your question about curl grubs.

How much of this drench did you apply, and over what area? Curl grubs can reside quite deep, and as the weather cools, they dig deeper. To really saturate the soil down to their depth, you'd need to pour around five nine-litre buckets over a square metre. You'll have more success at night and you might like to wait for the weather to start warming up again when they become more active.

The other option is the Eco-Organic Garden 250ml Eco-Neem Concentrate Botanical Insecticide and it does work. You'll need to apply it periodically, perhaps two to three times a year until you've killed all stages of the grub's life cycle. It's ineffective on the egg stage and they can remain in this state for up to three years.

Please let me know if you have any questions.

Mitchell