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

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?

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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

https://www.workshop.bunnings.com.au/discussion/comment/36107#Comment_36107

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

https://www.workshop.bunnings.com.au/discussion/comment/80903#Comment_80903

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

chelated

https://www.workshop.bunnings.com.au/discussion/comment/80903#Comment_80903

Hello, you’ll find most types are coming up to the surface about now and chomping away (in south eastern Australia). Early Spring is a feeding frenzy for scarab larvae. Let’s assume that you have some different types of curl grub at different stages of growth and depth in the soil. I’d try the neem oil drench now (remove as much mulch as you can and water the soil thoroughly first) and then in October when the soil temperature hits 16°c apply some nematodes which you can order online (google search for ‘nematodes to kill curl grubs’). Hit the grubs with nematodes as soon as your soil is warm enough for the nematodes to be active, and again in Dec when egg-laying is likely, and again in Autumn to make sure you got all stages of larvae & eggs. You may wish to remove any backyard solar lights as they attract the beetles. The nematodes will remain active as long as there are grubs in the soil (and they will go deep) and as long as the soil temp is above 16, so we have to hope the September neem oil drench penetrates deep to get the grubs that are overwintering deep in the soil. The nematodes will take care of the rest.

Hope this helps! I’m doing this process too after finding about 4 grubs per spade in my garden beds. I had been scratching my head as to why my plants and trees were all failing when I came across the scarab larvae. This lead to lots of research and finding the little genius nematodes. After observing some giant curl grubs come up to the surface a few days ago as well as some smaller ones, I have realised I have a multi-generational, multi-beetle problem that all began when I purchased a blended, fine rooted turf from a local supplier in Autumn two years ago. I lost the lawn to the grubs in the first 6 months. The turf must have been full of different scarab eggs. As a rookie gardener, who had built a new garden ground up, I had no idea of the scale of my problem. I dug out so many by hand and converted the former lawn to a native garden, hoping they’d leave those plants and lawn alternates alone, but no such luck. This year I’ve lost two grevillea and all my Corsican mint already. In the first year I lost my entire lawn, a hybrid dwarf apple tree, a hybrid dwarf stone fruit tree and a crape myrtle. I’ve started implementing the above multi-stage plan that I’ve recommended for you. I hope your problem isn’t on the same scale as mine and you can nip it in the bud between now and Autumn. Oh and I also buried some delicious-looking old dead roots and rotting leaves hoping they act as decoy food while I implement the plan. I’ve also waved the grubs at my local magpies, inviting them to dine. I’ve read that the grubs can create a ripple in the soil visible to birds. This is all cobbled together based on my research as well as random ideas I had along the way as I began to understand more about the different types of curl grub and their behaviours/lifecycles. I can’t guarantee it will work and please feel free to ignore my suggestions, but I think it’s my best shot at disrupting multiple, complicated lifecycles to eradicate all curl grubs and eggs. I wonder if your thick mulch layer when you put it back will act as a deterrent for egg-laying beetles in December. I’m going to take a leaf out of your book and apply thick hardwood chip mulch after applying the October nematode treatment.
hope this helps. Good luck!

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