Jul 302013

Citrus Gall Wasp

Many of our more persistent garden pests are not native to Australia but citrus gall wasp is definitely an Aussie grown garden variety pest. Originally, this native wasp was limited to Queensland and northern New South Wales and its preferred host was native finger limes.  But citrus gall wasp has rapidly adapted to the wider variety of citrus fruits now on offer.  Since the 1990’s it has successfully migrated from Queensland, through NSW and can now be found as far south as Melbourne where it is virtually endemic in the iconic back yard lemon tree. 

What: Adult citrus gall wasps are rarely seen as they less than 3mm in size. The adults are poor flyers but can be windblown from other citrus trees nearby. The adult wasps mate in early to late spring when the female implants her eggs in the citrus tree that she herself emerged from just days before. Each female can lay up to 100 eggs, usually under the bark of new shoots, and the larvae hatch after 2 – 4 weeks. Often the larvae are already present in newly purchased citrus trees in spring.  The wasp larvae grow within the soft stem tissue for 9 to 12 months until they too pupate and emerge as adult wasps the following year.  Now that the effects of climate change are being experienced, the life cycle may be repeated during a single year instead of just egg-laying in spring.

Plants affected: All citrus especially lemons and grapefruit.

Damage Caused: The wasp larvae grow within the citrus stems until late summer when gardeners start to notice unsightly galls appearing on their trees.  These galls or calluses are formed in response to the presence of the feeding larvae. Galls cannot be ‘cured’ or reversed.  Old galls are unsightly but are also empty as the adult wasp will have left through the tiny exit holes.  Developing galls can be removed but this may also mean the loss of developing fruit at the end of the infected stem. Citrus gall is more damaging to younger citrus trees than older trees.

Control Methods: Controlling citrus gall wasp can be difficult but damage can be minimised by:

  • Avoiding high nitrogen fertiliser in spring as this promotes soft sappy growth – just perfect for the egg laying stage.  Feed trees in late autumn and early winter instead.
  • Removing all newly formed galls that don’t show signs of exit holes before the end of winter.  Old galls have already been exited.  Prune only a maximum of 1/3 of the tree to avoid stressing it too much.
  • From mid-August, hanging yellow sticky traps with a chemical attractant inside to trap emerging adult wasps. The yellow is an attractant and the sticky coating makes it impossible for the wasp to escape.  Remember to twist the top so that the chemical is released. Since beneficial insects may also be attracted to this trap, do not leave on after November as the wasps are no longer about and even small birds may become trapped.
  • Destroying infected stems by burning or bagging.


Pic 1, 2 & 3: Elaine Shallue, SGA

  76 Responses to “Citrus Gall Wasp”

  1. I am currently trialing coating the areas in question on my lemon tree with a light covering of olive oil, creating a barrier to block air and hoping the wasp/wasp larvae suffocate. looks promising, many wasps have come out [I am thinking to breathe] and are dead stuck in oil on the outside of the stems.

    • That’s interesting – it doesn’t help your lemon tree in the short term but does reduce the number of wasps for future infections.

  2. I’m currently experimenting with 10:1 Acrylic paint/neat Confidor mix painted onto the galls. No idea if there is any likelihood of success but as some galls are very inconvenient on a young espalier I’m looking for an alternative to radical surgery. Thinking that the insecticide may do the larvae a mischief if it migrates into the gall but if that’s not possible then the adults may get a lethal dose on emergence.

    • SGA does not recommend Confidor since it has been shown to be harmful to bees because of its neonicatinoid content. It is banned in the European Union and there are calls for it to be banned in Australia.

      Since the gall is in a spot where it would be inconvenient we suggest you smear a layer of petroleum jelly on the branch to suffocate the wasp when it emerges then wrap the stem with a few layer of grafting tape or cling wrap to stop it emerging. Whatever you do we couldn’t support the use of chemicals.

  3. I have a dwarf citrus tree with wasp galls on it. I’m wanting to replant it into a garden container with other fruit trees. Should I keep it away from other plants?

    • Certainly keep it away from other citrus. You should inspect the galls and prune out any that do not yet have holes in them i.e. they still have larvae which if they mature into wasps will spread the problem.

  4. Hi to remove all the galls from my grapefruit tree means there is nothing left of the tree so is it just better to leave some in

    • If the galls have holes in them you could leave them as the insect has left. Citrus will tolerate hard pruning and will respond with new growth quickly. If you get frosts you would need to protect any new growth until after any danger of frosts.

  5. I am experimenting with my badly infected grapefruit and lemon trees. I have shaved some galls open with a very sharp potato peeler, to expose the eggs. My 5 year old grandson asked why didn’t I just wrap sticky tape around the galls to stop the wasp getting out, which I have done with a couple of branches. I am feeding them in Autumn and early Winter and will be pruning out as well. My Tahitian limes, mandarin, orange and cumquat are all OK.

    • Wrapping active galls will not stop damage to the tree, but exposing the larvae before they have metamorphosed into wasps will kill them. Please read the article above carefully and the comments and responses for further ideas.

    • Exposing the galls with a peeler will kill larvae that have not yet metamorphosed into wasps. There is no point in wrapping them. Please read the article above and the questions and answers carefully for more ideas.

  6. Hi , my lemon tree is full of the gall wasp. It’s not producing much fruits and most of the stems are thickened. Is it okay if I prune the stems at this time of the year? Would it damage the tree?

    • At this time the wasps have probably gone. Inspect the galls to see if there are signs of exit holes. If the tree has been heavily infested, it might be a good idea to prune it back while the weather is still warm as long as thereis sufficient water to ensure its recovery after pruning.

  7. I cut the twigs off, bruise the bark with pliers, peel off the bark to expose the pupae and leave the pieces in the sun for 3 or 4 days to dry out.

  8. I cut off the affected twigs, bruise the bark with a hamner or pliers, peel the bark of to reveal the holes in the wood and let tgem dry out on the sun.
    I figure that the wasp larvae cannot survive the drying twigs more than several days and put the dried material in the bin.
    I may also try cutting the twigs off and putting them in the oven at say 100 degrees C for an hour or so.
    Barry Eltham North Vic

  9. We’ve got a young lemon (in container) and a lime both around 1 year old, both of which have some obvious galls, but I’m not sure how to differentiate small galls from normal mature growth as in the bottom part of your top picture.
    If I cut out the obvious galls now, should the tree put out new growth below ? Some galls are on major branches. (I’m in Adelaide).

    • If the gall has a small hole in it the wasp has emerged so doesn’t need to be removed. But if you are unsure, then prune them all out. Citrus trees are good at recovering and it wouldn’t take long for the tree to recover.

      • Thanks, but doesn’t the presence of old galls weaken the branch ?

        • Leaving a lot of old galls on a tree will weaken it, but if there are only one or two, then it shouldn’t be a problem. There is some debate about this, and many people recommend removing all galls. Trees that are well-established are not affected as much as younger ones by the presence of galls.

  10. Hi I went to my local nursery and they said to use Neem plant spray. Will this work in preventing the gall wasp from attaching my tree again. I have trimmed all the affected limbs.

    • Unfortunately, no. The only preventive measure at present is very fine netting and even that may not keep them out, but it excludes beneficial insects. Scientists are working on chemical preventatives.

  11. I have this nasty pest and I am hoping to apply an experiment next hatching season but I need some advice.

    I plan to wrap the trees in that fruit netting stuff I see around in fruiting season and inside hang an old fashioned fly trap like the ones my grandparents used. An adhesive strip – but in this case maybe double sided tape or whatever is handy so they land on the tape and that stops the migration process. Once the wasps are finished doing their thing, simply remove the mesh. Reckon it’ll work?

    My question is, as these things are 3mm long do you have a recommendation for a mesh that will stop them from escaping the enclosure?

    • Netting the tree may be a good idea but it also excludes beneficial insects such as bees and other pest predators. And the netting will need to be very fine with 3mm or less holes.

  12. I have only noticed the galks on my young lemon tree today. I realise the wasps won’t be in them. What is the best way for me to handle the tree now? Do I prune or should I wait till autumn?

  13. I have just re-potted 5 grafted citrus trees that I bought from Aldi. The orange and the Lemonade do not have the wasp as best I can tell. The lemon, lime and mandarin definitely do which led me to search online for the problem eventually leading me to your site and to find a solution is quite elusive.

    This is my thought and question to you. What about surrounding and securing the tree with one of those fruit nets and hang an old fashioned fly catcher inside the net. It is essentially sticky paper and the fly lands on it and cannot get off. If the wasps are trapped and are mobile during their adult stage (and they must be to infest neighbouring trees), wouldn’t this low tech method catch them all?

    The net could be used during the right season and if everyone got on board the problem could be solved and fruit net sellers would get rich and we would all become experts at making sticky traps!

    • Your ideas are interesting but consider the following factors. Citrus gall wasps are only about 3mm long so you would need mesh like ‘voile’ to stop them completely. There is netting available that has holes about 1 x 3mm which would probably make it difficult for the wasps to get through. Those fly catchers are quite non-specific and catch other insects too. There is a lot of research going on to develop specific attractants to put inside sticky fly catchers – we must wait until something is developed.

  14. Hi all, My lemon tree is about 30 years old. in Central Coast
    last year I sprayed with veg oil, washing up liquid and water, all was fine.
    (My 1st year in Australia)
    1) This year it had sooty mold stuff.

    2)sticky secretion on old branches.

    3)and galls!!

    there were 75 lemons all seemed fine.
    I did net the tree as Cockies were eating new rock hard fruit!!
    I didn’t know about galls until reading this=
    yes tiny holes in them , so should i just leave those branches.
    It seems a main branch has died bark is coming away and pitted with tiny holes.
    also there is new growth to opposite side of tree near base is this
    new branches just shoots or are they healthy new ?

    • We’ll start with your comments in order. 1&2). Sooty mould is the result of scale or aphid infestation. Ants love the sweet, sticky secretion from both pests and will spread it throughout the tree. Spraying your tree with white oil before the season gets too hot would sort out both the scale and the aphids. Without a food source the ants will soon disappear. A good wide band of petroleum jelly around the trunk will also stop the ants returning. Renew this as it starts to wear off. Spraying white oil on citrus trees in the hotter weather will cause them to lose their leaves. 3). Galls are the bane of citrus growers in many areas. Remove all visible swellings now and keep an eye on new growth. The gall wasps prefer new growth to lay their eggs in. you will need to use diligence through the season as any missed swellings will produce more wasps in the early spring. This seems laborious but vigilance is the only real way to be quit of them. Fortunately the adults are fairly sedentary so re-infestation will probably only be mild. Also refer to the notes regarding Citrus Gall Wasp on this site.

      • This has been a very enlightening thread. I think it was Sharon P who suggested pruning twice a year. I live in Melbourne. So when would you prune? And was Sharon referring only to the branches with galls or did she mean pruning the tree all round?

        • Definitely prune branches which have galls before the end of winter. If your tree is getting too large then prune other branches too.

  15. I’ve heard that painting the galls with horticultural glue will trap the emerging wasps and break their life cycle. I’ve also noticed that the growth beyond some galls seems supercharged, as if the larvae release a stimulant. I don’t like cutting out these vigorous shoots so might the glue be a possibility for these cases?However, there is the possibility that the wasps have just chosen the strongest shoots but something tells me that’s not the case.

    Any experience with glue?

    • I haven’t heard of any success with painting and some have success with traps while others don’t. An integrated approach such as only fertilising citrus in autumn and not spring will reduce the amount of soft sappy growth which they love. Removing all galls as soon as you can in late autumn or early winter will also reduce the adults re-infesting as they emerge in late winter.

  16. How do I tell a gall wasp “gall” from a normal woody hardening of a green branch? Some pictures show a very obvious big lump but others to me just look like normal growth and aging of a branch.

    • In basic talk a gall wasp host site will be a ‘bulge’ rather than a general thickening of the stem. Gall wasp damage will also be on young supple growth that the wasp larvae like. After they emerge there will be a ‘pinhole’ but that is not much help to you as the wasp will be gone by then.

  17. Dear Sharon,
    A technique I used on my lime tree last year seems to have worked well. I used a stanley knife or even the sharp secateurs to slice along the gall and expose the chambers to the air…as with all plants, the lemon tree will seal off it xylem tissue and so the surface of the gall chamber dies up and the life cycle of the wasp is interrupted. It took me 3 weekends to do this to my 40 y.o lemon tree as well as cut off some of the branches that were heavily infested. I then sliced open the galls and left it in a special bin for 3 weeks.

    I hope this attempt will again reduce the wasp population in the area….I talked 2 neighbours into trying it as well…we will see how it goes…

    • What you have done is a great way to deal with citrus gall wasp if you get to the gall early enough and if you are patient and skilled enough with a knife (you obviously are) enough to avoid cutting into the gall too much and severing the branch. Thank you for sharing this.

    • Hi Walter, I am interested to know more about this method. I have a small young dwarf Eureka lemon tree in a pot (I’m in Adelaide) that has become heavily infested.
      I have removed about 1/3 of the branches, targeting the most heavily infested ones, as per some of the recommendations here. I am hoping that the tree will put out new growth over winter and be hardened against attack in case wasps emerge.
      So I still have branches left with galls and would like to try your method to disrupt the lifecycle and so avoid having to cut more of the tree off. But I am wondering if you could provide a little more detail about the method. How close together should the cuts be on each gall in order to ensure that sufficient oxygen gets in to disrupt the larvae? How deep should they be? And how can I tell if the actions have been successful in killing off the larvae so that none will emerge?
      I am applying liquid citrus food fortnightly and keeping it well watered as it is in a sunny position on a north facing porch.

      • The method Walter describes will disrupt the life cycle of the wasp and reduce its spread, but is not a foolproof preventive for the long term. Even if you get your neighbours to do the same thing, wasps may still be carried in on the wind or when other neighbours plant infected trees. But every attempt to slow the spread of this pest is welcome.

      • Doing what Walter suggests will disrupt the life cycle, but is not a foolproof long term solution. Even if you persuade neighbours to apply the same treatment, wasps can still be carried in on the wind or brought in on infected new trees and start infection again. But it is definitely worth doing since every attempt to reduce the spread of this pest is welcome.

  18. Is it wrong to prune for Gall in Adelaide late June/winter? I’m concerned to get rid of the gall on my citrus before Spring but also thought that pruning in winter isnt ideal. I have been searching all over the internet to see if pruning for gall now is ok but have not found any clear answer. Thanks EJ

    • Removing gall wasp swellings is better in late autumn or early winter but remove them by all means when you can. The tiny wasps emerge in late winter so if there are no ‘exit’ holes on the swellings go for it!

  19. I think an Australia wide campaign needs to emerge to remind everyone to remove all citrus gall wasp galls before the start of August each year.
    otherwise growing citrus in Australia is going to become increasingly disappointing.
    Our two year old lemon, mandarin and pink grapefruit trees have all been affected. All three trees purchased from reputable sources, and none showed any evidence of any citrus gall damage when the trees arrived.
    I think people need to regularly inspect their citrus trees, several times during the year, and then again in June and July and definitely before before August.
    I think all galls should be removed by the end of July. August is too late.
    Even neighbours could offer to remove active galls for any elderly neighbours who are not up to pruning a big lemon tree.
    However I think pruning twice a year may need to be considered.
    How can we be certain that Wasps might lay eggs very early or very late in spring? Or even lay in August?
    While hatched wasps could emerge very early in late July or very late in September?
    I am sure they do not all emerge from every gall on the same day.
    We pruned every last gall we could find in March. Yet by June we found some more swelled galls. They were not as large as the ones we pruned in March but they were definitely galls.

    Also the importance of double bagging the removed limbs of the citrus, and putting same into the garbage, should be stressed. Perhaps composting depots need to put up signs telling people not to bring citrus cuttings to a depot? Otherwise the wasps can remain snug in the gall and later emerge to ruin another citrus tree.

  20. Hi I have recently discovered our lemon tree of over 10 yeas is completely infested from gall wasps.. But seem to have all gone. I am currently in the process of burning the tree limbs. I have cut the tree right back.
    My concern is I picked all the lemons, and I want to know if they are safe to eat or should they be thrown/burned too..?
    Thank u in advance.
    Regards, Jai.

  21. I have a lime tree that is espaliered along a fence. I have a small gall wasp nest that has formed on an important branch of the tree and I don’t want to loose it as I’ll also loose the shape of the espalier. Can I cut away the nest without cutting right through? i.e. leave the branch to continue if possible.

    • Gall wasps lay their eggs on the soft growth where the larva burrow in and feed. When they are mature they exit the stem, leaving small holes. Short of re-infestation by a new generation they will be finished with the site. I would suggest that you smear petroleum jelly on the site to discourage a new infestation and then just let the swelling ‘grow out’ as the tree gets older.

      • I had a Lemon tree that was so infested by Gall wasp lava that it eventually ceased producing lemons entirely, instead it produced galls ! there was not a stick on that poor tree that was not infected and dedicated to gall production. eventually for the benefit of the other lemon trees in the area it had to go. (I was renting)
        At my new house I have another tree that is also infected. I was thinking to try diatomaceous earth on the new growth this time, maybe spray the tree with honey / water mix then sprinkle the diatomaceous earth to get it to stick to the new growth. I dont know if anyone has done this before ??? I havent heard or read of this being done and would be interested to know if anyone has.

  22. Have a Patio lime tree in a large half wine barrel. It has had gall wasps for some time. Iam in Albury NSW.
    probably about 2-3 years old. Have been told to mix up a spray of copper sulphate and spray it, would this be ok?

    • Controlling citrus gall wasps is a process. The swellings from their presence shows up in late summer. Removing affected stems then will control them as they would normally emerge in spring. This will give the plant a chance to make some new growth before the winter sets in. In areas with frosty winters pruning them now to stimulate new growth which may be affected by frost. It is too late for that now as it is nearly mid-May so make sure they are removed before August when the wasps emerge from the gall. Adult wasps are short lived and don’t travel very far, preferring to stay on the same host. Small holes on the gall show that the wasps have emerged. It is best to follow the procedure described in our article. Sprays don’t work and will harm beneficial insects.

  23. I was told that painting new Gauls with plastic paint before the wasps emerge will trap the wasps in the Gaul. I’m not confident about doing this as I’m afraid of poisoning the tree. What is your opinion on this.

    • Hello Bev,
      I have not heard of painting galls but accept that it could work if someone was using enamel type paint which may be toxic to the insects when they chew out. I have heard of people years ago using lead based products to control insects on fruiting trees but thankfully lead-based concoctions were banned years ago. Traps or removing all affected growth by August is probably the safest way to go.

  24. Hi SharronP,

    I’ve read your article but nowhere can I find, what damage gall wasps do besides looking unsightly. I have a 50 year old lisbon lemon tree that this year has suddenly been infested with galls. Do I need to cut out the branches with the galls?


    • You are fortunate that the tree has been free of galls for so long. The galls interfere with normal metabolism of the branch and can slow growth, gradually making the tree less productive. So as the article states, it would be wise to cut the infected branches out.

  25. I planted a new patio lime and dwarf Eureka lemon last Spring into large pots. About 6 weeks ago I discovered galls forming on the branches. I suspect it is gall wasp as I removed a lemon tree from my garden last year which was infested with them ‘. The galls have become rapidly bigger and prolific. I know to cut them out but is it OK to do it at this time of year? I am in a Adelaide and I think the hot weather has finished. Should I prune the trees in stages so as not to stress them too much? Thank you.

    • Yes, prune them out if there are no holes indicating that the wasps have already emerged. Make sure that you don’t prune more than 1/3 of the tree off. If there are still galls present after pruning 1/3 you could wait a few weeks, but not months in case the wasps emerge before you get a chance.

  26. I have gall wasp on my lemon tree & this morning I was having my morning lemon & water drink & as I was sucking it through a straw I noticed what looked like a worm. On closer inspection it was & I’m troubled now at the thought of having ingested these worm things before I saw this one & am wondering what happens if I have? Can you help?

    • It definitely had nothing to do with gall wasps which don’t enter the fruit. If it was, indeed, a worm (it could have been a bit of seed or something else quite harmless) it wouldn’t be a health problem because the extremely acid conditions in your stomach would kill it.

  27. Do the galls affect the thorns? I pruned my tree back to the trunk a few months ago, its since come back nicely but on two of the new branches there is one thorns with a thickened woody appearance that looks like it could be gall wasps, but I’m unable to find reference to them affecting thorns.

    • It would be very difficult to distinguish stem and thorn if the gall in the stem under the thorn.

    • I have removed several thorns like this from my trees, I just cut them as close to the branch as possible hoping that any in the branch itself would dry out and die.

  28. What is the best time to prune fall wasp in melbourne

    • Towards the end of winter is probably best, but because the wasp is becoming more widespread and the climate is changing, it would be wise to inspect trees moderately frequently and prune out any galls that DO NOT already have holes in them

  29. Hi guys.
    Just a quick one but I’m a consultant in the commercial citrus industry plus heavily involved in Citrus Gall Wasp control options.
    The only reason I’ve found this page is from a client who printed this page out and brought it into my work asking for pheromones.
    Firstly there are no pheromones currently available that work against Gall Wasp. Citrus Australia have spoken to an entomologist from Adelaide University recently to do research on Gall Wasp and pheromones however this work is yet start.
    They are also not attracted to yellow sticky traps. Insects that are attracted to flowers will be attracted to yellow sticky traps and Gall Wasp are not attracted to flowers.
    Currently there are only two proven chemical control options and neither are suitable for non commercial orchards or trees.
    I just thought I’d reply to this post to make a few corrections.
    SharronP has made the perfect recommendations for home trees and pruning galls off is the only non chemical way of controlling them. Spraying trees during the wasp emergence period with Bifenthrin is also effective but needs to be applied weekly and is extremely disruptive to beneficials.
    There are native parasitoids being bred up to counter Gall Wasp but in our region we are finding that by the time they become established the trees will near on be a write off.
    Hope some of that information helps. They are a serious pest of citrus and a number of orchards are at a point that they are no longer economically viable.

    • Thank you, Matt, for your comments. You are right that the attractant is not a pheromone but another chemical. I have changed the post accordingly. What you say about commercial orchards is absolutely correct and the wasps are not particularly attracted to yellow alone. However, the manufacturer of the yellow traps with added attractant has done research which shows that yellow was a more attractive colour for wasps than blue or green. The manufacturer also say that test were also conducted in commercial orchards and found that the traps were not effective in that situation, but were effective in home gardens where the number and density of lemon trees is VERY much lower. We would not recommend bifenthrin at all because of its non-specific effects.

      We look forward to the results of research on parasitoids and pheromones.

    • Ive heard that spraying an oil helps prevent some Citrus leaf miner wasps laying their eggs, could this be the same for a gall wasp?

      • Oil sprays will not help a tree with gall wasp. The only way to deal with gall wasp is to remove the galls if the wasps have not already left the gall. In some cases, a yellow sticky trap containing a wasp attractant, hung on the tree in late winter, might also help a bit. Oil sprays (white oil, or better, a homemade one with vegetable oil, will prevent scale, but not gall wasp.

  30. In the long run you have probably done the right thing – sometimes you need to “be cruel to be kind”.

  31. We’ve been advised that on mum’s lemon tree (she has 1 large & two smaller trees and full of lemons) that she has Citrus Gall Wasp. We are arranging for the pruning/removal of the citrus gall wasp. Once this has been done, is it ok to eat the lemons. I’ve been told that the wasp releases parasites that penetrates through to the fruit. Is this true?

    • Citrus gall wasp does not directly affect the fruit. Its effect on fruit is to decrease production. When the wasps emerge from infested galls, they mate and lay eggs under the bark of the tree where new galls will form after the eggs have hatched. The larvae stay in the new galls to pupate and eventually emerge as wasps. At this time of year you need to be checking the galls to see if there are signs that wasps are still in them or new ones developing and prune them off. There is little point in pruning galls where you can see small holes where the wasps have emerged.

  32. Hi. I have the gall wasp infections on my lemonade tree, here in the west of Brisbane. I have been unable to prune due to an injury, but now I find that the tree has a large second crop coming on. Would I be best to wait till next year to prune off the affected branches. Also, if the wasps have already hatched this year, is there any harm leaving the empty galls on the tree? Thanks for your help.

    • I’d be leaving pruning the galls out for a while. If you do it now you may be sacrificing many good lemons. Observe the tree carefully and if you see new galls appearing, then prune them off. Make sure you put the pruned galls into a plastic bag, seal it and dispose of in the rubbish (not compost or green waste bin).

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