Most likely culprit is Citrus Leafminer - a type of moth. Does it look like something is burrowing through the leaves, leaving silvery trails? It ends up making the leaves curl. If you're not sure, take a damaged leaf into a store. Spraying petroleum-based oil on the leaves can prevent the moths from laying their eggs but it might be too late and you might need to focus on helping the tree recover. - Isobel
Here's a video on citrus leafminer.
I have used Pyrethrum. I'm told that it's natural and should do the trick - boris
My personal fave is eco-oil. Just read any precautions about spraying on hot days, etc. You should only need to spray the new foliage and repeat applications may be needed. The damaged leaves won't repair so you'll need to prune them off for appearances sake.
Should just add... if you don't want to use any sprays, even safe ones, then you can prune off all new foliage however collect all leaves, seal them in a bag and place in the rubbish. - Adam_W
I got some moth traps at Aldi, not sure if they've got them all the time or not. Probably get them at garden centres as well. They work really well.
We had a problem with moths inside, they weren't attracted to the lamps and I was tearing my hair out wondering what to do, so we put some of these traps up and next morning there were about 25 moths stuck to them. That's a good enough indication that they work - bergs
There are a few things that can help to deal with citrus miner:
1. Feed your trees through winter and into early spring with organics then calm down once they appear.
2. They are after the urea inside the leaves, so feeding with high urea into spring and through summer is going to cause trouble.
3. Don't feed high urea in autumn for the growth flush then. In fact it's best not to encourage autumn flush due to the miner.
4. I have tried all the oils. Pest oil / eco oil / white oil, etc. They have limited success. What I have found to be best is a mix of eco oil and neem oil. Neem oil soaks into the leaf and kills the grub, eco oil leaves a coating on the top of the leaf. They need to be sprayed every 10 to 14 days when they appear but not when the tree is flowering. Eco neem is expensive for a small bottle but you use less - both eco oil and eco neem can be bought at Bunnings.
5. If you spray the flowers when open they will die and bees won't come. Been there, done that. Never spray flowers with anything, even food (disrupts the growth).
6. Remove infected leaves. They will curl up too. You can buy sticky traps from the eco people that capture the males so less breeding but they are expensive. Seems strange to kill the males. Would have thought females would be better but hey! Spray your trees underneath and top of leaves in the cool of the day and away from the sun with neem and eco oil mix. They are both organic. So 6pm is good. These oils don't have a long withholding time from picking fruit either.
7. As an avid grower for a long time I hate citrus leafminer as they attack my new growth! It’s best to get them growing well in August/Sept and get the leaves big and strong before the miners turn up! The neem and eco helps but do it regular to minimize infestation. But you will never eradicate them. Hope this helps. Remember they are after the urea. That’s why people pee on them but maybe feed with low urea in the nitrogen column could help. Unfortunately citrus really like urea as well. Bloody minor. - laidbackdood
Neem oil seems to work for me and Epsom salt every now and then. I also use worm juice as a fertilizer and get consistently high yields for all my citrus (2 lemon, 1 lime, 1 kalamansi, 2 kaffir lime and 1 tangor kiyomi). - chefyash