I’ve chatted to horticulturists about gall wasp as we have had difficulties with the wasps too and they recommended the pest strips. They are inexpensive so certainly worth a try. They are a lot less invasive than harsh pruning.
Citrus gall wasp is a big problem in Melbourne (and Australia). They keep coming back because you'll have neighbours somewhere with the same problem - and they may or may not be addressing it.
I'd recommend talking to your neighbours and getting them to talk to their neighbours and so on so you can try and eradicate it from a wider area. - bluebec
The yellow strips seemed to help a lot for my little trees. I also used a scalpel and chopped off any I saw if it was still a small lump. - Eric
Definitely use the strips. You must also cut it out though. If you leave it the new ones hatch and it keeps creating the problem. Need a neighbourhood campaign to really get rid of it. - timjeffries
I worked with an entomologist a few years ago on a citrus gall wasp (CGW) trial with interesting results. The trials were directed to the citrus industry so have chemical levels in fruit in mind for export.
A product called Surround Kaolin Clay was trialed on moderate to heavy infested trees with good results and a number of systemic chemicals were sprayed and also applied via drip, with ranging results.
Parasitic wasps were also released with good results long term. Confidor Guard was the most outstanding performer through the drippers. I am not sure what the outcome of the application to the APVMA for licence to use it on citrus is though.
Guard is expensive and the smallest container is 5L. I have used Confidor (not Guard) this year at 16ml per tree watered into the ground in late October and have noticed that most of the galls are still intact
In the Sunraysia lemon trial the reduction of galls with the Confidor Guard was visually noticeable from one year to the next. - Stephen-H
I have had gall wasp issues on my lemon tree for a number years. I have pruned, cut back to bare trunk, removed the gall but they still kept coming back. I did some serious research into a product called Kaolin Clay also known as Surround.
I remember my late father spraying everything from fruit trees, grape vine to tomato plants with a homemade brew of garden lime and copper sulphate crystals. This inspired my research into kaolin clay.
I tracked down and purchased this kaolin clay ($110 for 12.5Kg) expensive but worth every cent. Start of September last year I mixed 10g per 1L of water and sprayed my lemon tree and other fruit trees with this mixture.
You should spray your lemon tree(s) between September and December for maximum protection from gall wasp. It is now May and I am happy to report that my lemon tree is FREE from gall wasp. I highly recommend this product and does not need to be mixed with other pesticides like white oil but you can if you wish to give your tree added protection against leaf miner which appears to become active during March/April.
Kaolin Clay deposits a very fine layer of the product over the whole tree, leaves and Trunk. Any gall wasp that may be infesting the tree at that time will suffocate as they cannot tolerate the fine powder and it also stops the female wasp from nesting or laying its eggs on the new shoots, thus eradicating this pest. - Nino
I don’t know much about the clay but this is how I treat mine. I had a problem for quite a few years and used to prune them off. It was a vicious circle though, as the wasp loves the new growth. Now I just inspect the trees regularly and scrape the gall to expose them and they die. - LisasGarden
I'm planning on scraping back the galls on 2 of the trees as they're still quite small and newer, however the main tree is really big and I'm not confident I'll be able to manage scrapping them all - especially around the top of the canopy, hence wanting to try the Kaolin Clay too. - kate5
If you decide to give up and bin a problem citrus, I would wrap them up and dispose in the rubbish bin rather than the green waste bin so you're not spreading them. The wasp larvae grow within the citrus stems until late summer - that's typically when you start to notice the galls. If they are old galls though there's no issue - the adult wasp will have left through the tiny exit holes that you'll see on them. - greygardener
I put infested branches in a bin filled with water to drown the larves. Leave them for 6 weeks and pour them into the compost bin. - QuailFlock