Experiment: Control of Citrus Gall Wasp 40

Recently, I posted some observations and theories that I have been developing on citrus gall wasps. To test out the theories, we’re setting up a trial to see which treatment regime might produce the healthiest and most productive trees.

Setting up the Gall Wasp experiment

We used 10 x Meyer Lemon trees in the experiment. They seem very prone to Citrus Gall Wasp.

In August 2017 we purchased 10 Meyer lemon trees. At the time of purchase, they were relatively identical in size, shape and stage of growth. The trees were randomly paired up and allocated to five different treatments:

  • Treatment 1: Citrus Galls pruned out in June every year, fertilized monthly Sep to May.
  • Treatment 2: Citrus Galls pruned out in June every year, fertilized monthly in Dec and Jan only.
  • Treatment 3: Citrus Galls not pruned out, fertilized monthly Sep to May.
  • Treatment 4: Citrus Galls not pruned out, fertilized monthly in Dec and Jan only
  • Treatment 5: Citrus Galls not pruned out, fertilized monthly Sep to May and treated with calcined kaolin clay (Surround®).

The trees were potted up into 40 cm pots and filled with Fulton’s Bulk potting mix. We chose Fulton’s Bulk potting mix as it was an average performer in our recent potting mix trials. This meant that we could control the amount of nitrogen rich fertilizer, that we applied during the first few seasons of growth. A better performing potting mix would have promoted a flush of spring growth regardless of any extra fertilizer that we applied.

We potted up 10 lemon trees. Two trees are each going to be subjected to different treatments.

The plants were placed together to ensure that all experienced similar growing conditions, sunlight, microclimate and irrigation.

There are several large citrus trees growing less than 50 metres from where the experiment is set up. There are other citrus trees visible in nearby neighboring yards. They are all likely to have some Citrus Gall Wasp in them.

Citrus Tree Pruning Regime

Treatments subjected to the “Prune in June” regime (four trees in total) are to have all visible galls pruned from the tree in June. The galls are to be soaked in a bucket of water. None of the purchased trees had any galls present when purchased. We decided to mimic trees that have been infected to speed up the accumulation of results. So approximately one third of the foliage was removed from the trees subjected to the June pruning regimes (despite there being no galls present in the first year). The other six trees will not be pruned at all in June, in any year.

Our citrus trees following our simulated “prune in June” regime in the first year.

All ten trees will be tip pruned as required in/or around November and again in/or around February (if required). Whilst the trees are small, this will be done with secateurs or finger tips. As the trees grow, we may resort to using hedge trimmers. Pruning will aim to retain as much fruit and blossom on the tree as possible. This pruning is a typical regime that I use on most citrus trees (see our guide on citrus tree maintenance for further details)

Fertilizing Regime

Trees are to be fertilized according to one of the following two regimes

  • monthly Sep to May
  • monthly in Dec and Jan only

Trees are fertilized with Richgro Organic Fruit and Citrus Fertilizer, which was the best performing organically certified fertilizer in our recent experiment.

It will be applied at the rate of one handful per pot, per month. The fertilizer will be scattered around the surface and then watered in well.

Calcined Kaolin Clay (Surround®) Regime

The NSW DPI has been trialling some different treatments in commercial citrus orchards. One organic treatment method is showing promise. It involves spraying calcined kaolin clay (Surround®) twice during the citrus gall wasp emergence period. This disrupts the laying of  eggs  and has shown to reduce gall occurrence significantly. We’ve decided to include this treatment as it’s relatively inexpensive, easy to apply and it’s organic.

Calcined Kaolin Clay (Surround®) is to be applied fortnightly for a total of three applications. The first application is to occur in spring at the start of each October. UPDATE 05/12/17: Going forward we will adjust the application of spraying the kaolin clay treatment so that we spray fortnightly applications four times, with the first application in the third week of October (see December 2017 update below)

It is to be applied at the “sunburn rate”. To do this we mixed 8 spoonfuls of power in a small jar of water. This was then tipped into a sprayer and made up to a final volume of 2 litres by adding more water. The trees are to be moved away from the other trees for treatment. The clay is applied using the sprayer and allowed to dry before being returned to their usual position.

Want to try Kaolin Clay (Surround) for Yourself?

We purchased our Kaolin clay from Muirs in Monbulk. Unfortunately it is only supplied in large bags, enough to last a backyard orchard for hundreds of years.

If you would like to purchase only a small amount, we have it for sale at our Community Night and Food Swaps. See the events page of our website for more information on these.

Results of Our Citrus Gall Wasp Control Experiment

Update December 2017

The peak emergence for Citrus Gall Wasp in Melbourne looked to occur on (or around) the 28nd November 2017. We filmed the above video of wasps emerging from galls on our tree and mating. I monitored the developing galls and when emergence was imminent we moved all ten trees around the perimeter of our infested grapefruit tree.

Citrus Gall Wasp Melbourne

Our citrus gall wasp experimental trees were temporarily placed around the perimeter of our infested grapefruit tree.

The emergence date was about a fortnight later than we had expected. We had based our expected emergence date on NSW data. Future years’ emergence dates for Melbourne are also likely to be around the same time (late October-early December)  Going forward we will adjust the application of spraying the kaolin clay treatment so that we spray fortnightly applications four times, with the first application in the third week of October.

Citrus Gall Wssp Experiment Melbourne

Flushes of new growth evident on Koalin Treated Tree 5A. This tree is likely to show evidence of gall was infestation next autumn. We will adjust our application of the Kaolin treatment for future yers to better coincide with the gall wasp peak emergence.

The kaolin treatment from this year is likely to be ineffective against the gall wasp. Particularly with tree 5A, as it had a flush of new growth since the final Kaolin application. That new growth had no kaolin on it, leaving it susceptible to infection. I expect this tree to have at least a few galls evident next year.

The following trees had lots of new growth at the time of peak emergence. I expect that they will have a large amount of infestation next year:

1B, 2B, 4B, 5A

The following trees were absent of much new growth at the time of peak emergence. I expect that they will have very little infestation next year.

1A, 2A, 3A, 3B, 4A, 5B

At this stage there is no correlation between the amount of new growth and either fertilizing or pruning regimes. I expect this is because the experiment has only been set up in the last three months. Next spring, once the trees have settled into their growing cycles, a correlation will hopefully be more evident.

All trees have some small fruit set. Tree 2A has the biggest and strongest crop.

Citrus Gall Wasp Experiment Melbourne

All ten Meyer Lemon trees have some fruit set. The fruit on Tree 2A has the largest fruit.

Update June 2018

June is the traditional time to prune out gall wasp. So trees being subjected to Treatment One and Two had their galls pruned out in the last week of June.

At the same time as undertaking pruning we noted lots of observations for each tree. These have been tabulated below.

The following points from this round of observations are most interesting:

  • Trees that have been feed monthly from Sep to May had an average of 2.5 mature lemons per tree vs only 1 mature lemon on average for the trees fed Dec and Jan only. So reducing fertilizing seems to impact productivity significantly.
  • Two treatments did not have any gall wasps present. They were treatment 4 (the reduced fertilizer and no gall removal) and treatment 5 (kaolin treatment)
  • Feeding regimes did not seem to have an impact on susceptibility to Pink scale or induction of flowering.
  • Feeding regimes did not seem to have an impact on susceptibility to Citrus Leaf Miner. In fact, the most severely affected tree was on the reduced fertilizing regime.
  • The kaolin treated trees showed no impact of Citrus Leaf Miner whatsoever. I hope that some residual clay from the previous October/November has interrupted the life cycle of the moth (rather than it just being a coincidence). I am particularly keen to see what happens next autumn with the two trees undergoing the Kaolin treatment regime.
Citrus Gall Wasp Experiment Melbourne

Our ten meyer lemon trees prior to gall wasp removal and fruit harvest

Citrus experiment post removal of galls (for trees undergoing treatment one and two only) and post removal of all mature fruit.

Citrus Fertilizing Melbourne Yellow Leaves

Some of the lemon trees had yellowing leaves

Citrus Leaf Miner Prevention Melbourne

Feeding regimes did not seem to have an impact on susceptibility to Citrus Leaf Miner. However, the trees treated with Kaolin clay had no citrus leaf miner whatsoever.

Citrus Gall Wasp prevention Melbourne

Our Meyer Lemon trees, post gall wasp removal.

Pink Scale Citrus Leaf

This type of Pink Scale was present on many of the trees. Severity of infestation didn’t appear to be linked to any of the fertilizing regimes.

Tree NumberNumber of Citrus Galls present in treeLeaf Miner evident in TreeNumber of mature, ripe lemons on treeNumber of immature, second crop lemons on treeLeaf ConditionOther comments
1A2 x smallModerate40Dark leaves, new growth is lighter in colourFlowers starting to form. Pink scale evident
1B1 x smallVery little11Slight yellowing. New growth has been slightly burnt by frostFlowers starting to form. Pink scale evident
2A4 x small
1 x large
Severe40Light green coloured leavesPink Scale Evident
2B4 smallModerate03Slight yellowing but generally dark green leaves. Pink Scale Evident. Ladybug present.
3A5 smallVery little50Dark green leaves. Lots of new growthLady bugs present, NO scale.
3B3 smallVery little10Several leaves are yellow, otherwise mostly dark greenLots of flowers, NO scale
4AnoneModerate00Slight yellowing of leaves, mostly light greenPink Scale Evident
4BnoneVery little00Moderate amounts of yellowing in leavesLady Bug present, Pink scale evident
5AnoneNone30Slight yellowing of leaves, mostly dark greenPink Scale, Brown scale and Ant present
5BnoneNone20Slight yellowing of leaves, mostly dark greenFlowers starting to form

It is going to be interesting to continue observing the results of the trial. So far, the most promising results have been with the Kaolin treatment. However, we are only a year into the trial, so who knows what the coming years will bring?

Update December 2018

The gall wasps in our grapefruit, lemon and orange trees began to emerge in large numbers on 2nd December. This particular day was hot and windy. The high winds will help to disperse the wasps to infest other trees in the area. I suspect they may travel hundreds of metres, if not kilometres in the wind.

The 2018 peak emergence is three days later than 2017. Which shows just how much these wasps behave like clockwork. It also shows why “Prune in June” is such terrible timing for controlling the problem.

We noticed that wasps continued to emerge from local trees for most of December. Many galls stayed dormant and haven’t had any wasps emerge. We haven’t noticed this in previous years, but will look out for it more in the future. I suspect that this may be due to sterile eggs being laid under the bark. Perhaps this is enough to stimulate the tree to form a protective gall even though the eggs are unviable?

Update June 2019

Our gall wasp experiment is now two years old and we are starting to see some trends.

We recently moved all the trees into our warehouse to inspect them. Outcomes from these inspections are shown in the table below. During the inspection, we looked at the number of galls on each tree, the quantity of fruit and other observations such as incidence of pests.

Our citrus gall wasp experiment in June 2019 prior to harvest of fruit and “Prune in June” treatments to applicable trees.

After the initial inspection we performed the “prune in June” to the trees undergoing treatment one and two.

Our citrus gall wasp after the “Prune in June” treatment was applied to the trees in group 1 and 2.

Fruit were then harvested from the tree. Interestingly some of the trees (especially treatment 3) had lots of fruit, but they were very small. So we also weighed the total quantity of fruit harvested for each treatment.

Our citrus gall wasp experiment post harvest of fruit

Tree NumberNumber of Citrus Galls present in treeLeaf Miner evident in TreeNumber of mature, ripe lemons on treeTotal Weight of Crop for both trees (Kg)Other comments
1B5Moderate141.71 kg
2B3Very little81.10 kg
3A10None71 x fruit smaller than most
3B3Very little141.09 kgAll fruit small
4B4Moderate112.08 kg
5BNoneModerate102.76 kg

There were a few interesting observations that we made about our citrus gall wasp experiment this year:

  • Fertilizing regimes had a small impact on the quantity of fruit harvested, but didn’t have the clear cut influence that was observed last year. Could this be due to biennial cropping beginning to occur in the trees on the high fertilizer regimes?
  • The trees NOT undergoing the “Prune in June” approach are generally larger in size than those being subjected to prune in June (especially after this treatment was carried out). The trees not subject to prune in June also had slightly more fruit (by weight and total number
  • All trees except for two (2A and 5B) had galls present. Treatments One and Three both had large numbers of galls compared to the other treatments. The Kaolin treatment (Number 5) only had one small gall between the two trees.
  • All trees were suffering from scale regardless of their treatment
  • The Kaolin treatment (Number 5) still continues to be the most positive treatment regime. It had the least number of galls (only one) and by far the highest yield of fruit (both in number and by total weight)

All of the trees were suffering from scale. Most of them also had signs of leaf miner and sooty mould.

One of the trees (4A) was showing signs of collar rot. This is usually caused by poor airflow around the trunk. It indicates that it is time for us to give our depot a tidy up and make some more room for the trees to be spread out further.

Some of the citrus galls were quite large

Kaolin clay was still visible on many of the leaves of the trees in treatment five.

Stay Tuned!

This experiment will run for several years. We will be regularly observing  overall tree health as well as  productivity. Periodic updates will be added to this page as the results develop. We will also share them on our Facebook Page and in our newsletter. Sign up to the newsletter so that you don’t miss out on seeing the results.

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40 thoughts on “Experiment: Control of Citrus Gall Wasp

  • Martin T.

    My lemon tree is in the east of Melbourne and the gall wasp population is growing year by year. I do not believe June is the correct month to prune. Take this year I had to prune now to prevent them escaping the tree bark. While pruning a flying gall wasp landed on a branch which I squash with my finger. I don’t believe it came from my tree as they were not hatching out, but from some one else’s tree. With the dry weather maybe the wasps have multiple cycles in a year now ?

    • Leaf, Root & Fruit Post author

      Hi Martin,

      It is interesting that you say you’ve noticed gall wasps emerging now. I’ll keep an eye out on other trees to see if I can also spot some. Perhaps your flying gall wasp was another closely related species rather than the citrus gall wasp?

      Thanks for sharing your experience


  • Murray

    thank you for your time in this matter i will be intrested to now if you have tried taping the affected branch as so the little bastards cannot escape?

    • Leaf, Root & Fruit Post author

      Hi Murray,

      Thanks for your suggestion. No we haven’t tried this. Our efforts have been focused on preventing infection in the first place. If you trap the wasps inside the branch, then the tree is still susceptible to attack from wasps emerging from other trees. It’s also going to be very labor intensive. If you do trial this method, please let us all know how you get on.

      Good Luck and Happy Gardening!


    • Leaf, Root & Fruit Post author

      Hi Jasmine,

      We got ours from a large, rural horticulture supplies. We had to buy it in bulk. We’ll be offering small bags of kaolin clay for sale at the upcoming Spring Into Gardening Festival, where we will have a stall.

      Hope to see you there!


  • Marlene Stagoll

    Your experiment is going to be fabulous and intriguing to follow.

    I decided a couple of years ago to reduce heavy Spring feeding as many pests love that sappy Spring growth
    – aphids, citrus leaf miner, citrus gall wasps, scale.

    I have just liquid fed our citrus which are in the ground with Powerfeed flower And Fruit.
    We will sprinkle a light amount of Sheep manure around the outside of the drip line of these trees.
    Sheepmanure is low in Nitrogen. Sometimes they get worm wee.

    I’ve decided a little feed more often is better for all of our garden plants and maybe we are
    Encouraging pests & viruses with heavy feeds.( & overwatering). Maybe we have all become too enthusiastic
    (& gready!) with lots of Fertilizer.

    I’d like to get hold of some of that Kaolin clay.
    Is it available to purchase in Melbourne?

    Best wishes for your experiment. I look forward to following the results.
    Cheers Marlene

    • Leaf, Root & Fruit Post author

      Hi Marlene,

      Thanks for sharing your insights and experiences. I agree, heavy feeding your trees is akin to feeding them junk food.

      We got our Kaolin clay from a large, rural horticulture supplies. We had to buy it in bulk. We’ll be offering small bags of kaolin clay for sale at the upcoming Spring Into Gardening Festival, where we will have a stall.

      Good Luck & Happy Gardening!


    • Leaf, Root & Fruit Post author

      Hi Jasmine,

      We got ours from a large, rural horticulture supplies. We had to buy it in bulk. We’ll be offering small bags of kaolin clay for sale at the upcoming Spring Into Gardening Festival, where we will have a stall.

      Hope to see you there!


  • Serge

    I have tried Calcined Kaolin Clay (Surround®) on my 10 years old Eureka lemon on 23.10.18
    I’ve noticed that my new growth leaves were badly affected/burned.
    I think it only happened to actively growing leaves – they curled up and and will most likely die.
    I used the recommended rate of application – around 30 ml per liter of water in a 5 liter sprayer tank.
    Any idea what could go wrong?

    • Leaf, Root & Fruit Post author

      Hi Serge,

      We haven’t had that experience at all, even on new growth on young plants. Had the sprayer previously been used for any other products (eg weed killer, copper sulphate?). Perhaps some residues were left which have harmed the leaves?

      Can you please email some photos through to us as info@leafrootfruit.com.au so that we can see the extent of the damage?

      Thanks for the update


      • Serge

        Hi Duncan,
        I did use the spraying tank for feed & weed product on my lawn just before but I thoroughly washed it afterwards.
        I will make some photos and post it to you.

        • Jenny

          Hi Serge,
          The weed’n’feed residue must still be in the sprayer. If I were you I would have two sprayers, one for weed’n’feed and one for less toxic applications. I hope your tree recovered.

  • Harry

    Great citizen scientist analysis, I live in northcote Melbourne. Over the last 20 years galls are now growing on orange trees and not just lemon trees.

    My observation over many years is that galls don’t grow on citrus trees at seaside areas of Victoria. Could salt air be a deterrent to galls?


    • Leaf, Root & Fruit Post author

      Hi Harry,

      Thanks for the feedback. I’ve seen many galls on trees in seaside areas and hadn’t noticed the same correlation that you have. I’ll now pay more attention though and see if I can spot a similar trend. Perhaps the milder climate impacts their life cycle?

      Good Luck & Happy Gardening!


  • Libby


    Just wondering if you’ve noticed if the citrus gall wasps have hatched this year yet?

    My trees had a couple of galls but they still seem intact.


    • Leaf, Root & Fruit Post author

      Hi Libby,

      Our gall wasps started to emerge on December 2nd and many people in Melbourne had them emerge around the same time. They continued to emerge over a prolonged period of several weeks. That being said there are many galls on our trees with undeveloped wasps in them. I wondering if they were eggs that were laid that weren’t fertile? Of if they didn’t develop for some other reason.

      Good Luck & Happy Gardening!


  • Jennifer Crockett

    I live in the Outer East of Melbourne. I have a dwarf Lisbon lemon and a dwarf Eureka lemon. They were in the original pot I got them in from the nursery for about 18 months, No galls while in the pots, but some leaves chewed off by some type of caterpillar. I planted them in especially built raised beds in November 2018. (We have heavy clay soil.) I fertilised them infrequently while in the pots, but once planted out have given them Dynamic Lifter and watered with seaweed solution. Now (early Jan 2019) each tree has several small galls. There are a few immature lemons on each tree above the galls. If I prune these out I will lose the fruit and the trees will be mere sticks. The trees don’t look particularly healthy as the older leaves are yellowish, though the new growth is green and healthy – just what gall wasps love, I hear.
    Having read through the articles and suggestions I am still not sure what to do.

    • Leaf, Root & Fruit Post author

      Hi Jennifer,

      Thanks for sharing your experience. I can understand why you are still unsure of “what to do” about the “problem”. We are eagerly awaiting the outcomes of our citrus gall wasp experiment as the rest of you. In time a clearer management strategy should be evident. Stay tuned!

      Good Luck & Happy Gardening!


  • Megan

    Can you please update the results of this experiment for those of us not on Facebook? I have galls on my Kaffir Lime in Croydon (VIC) and am looking to see the best way of dealing with them (and hopefully not infect my new lemon, lime & native ginger lime!)

    • Leaf, Root & Fruit Post author

      Hi Megan,

      Thanks for your interest. Next week we will be performing our “prune in June” on the relevant trees and then putting together an update after that. We will have the trees on display at our next community night if you would like to see the trees in person. Details can be found on our events page.

      Stay tuned and thanks for your patience!


    • David

      Thanks for documenting and sharing.

      My concern is that if you have trees that are not being pruned then they will be the hive incubators and keep infecting the nearby pruned trees. I understand that having them far away from each other is difficult but having the two populations close together in my view is unfair when comparing the results.

      I raise this because my neighbour pruned very hard on a mature tree and now it’s looking great hardly any wasp and full of fruit. My mature tree just kept getting worse and unmanageable so I decided to remove all the green 28 June. I believe by culling all of the population on my tree it will help reduce infection when fresh green shoots start.


      • Leaf, Root & Fruit Post author

        Hi David,

        Yes, pruning all the galls from your tree will reduce the local population load. However, the wasps are so prevalent in Melbourne that eradication will be impossible.

        Pruning your tree makes it more susceptible to attack from neighboring trees. Hence why we advocate for not pruning. Hopefully this expeirment will give us some clarity over the years to come.

        Please keep us all updated on the outcome of the hard pruning that you gave your tree.


  • Pat Wooding

    I’m late to this experiment, but will follow your results with interest.
    I have about 15 citrus trees in my garden, (a mix of lemon, mandarin, grapefruit – even a finger lime) all of them are young and very susceptible to gall wasp.
    Last year I used the yellow sticky traps but with very limited success. I pruned where I could and probably too early but I’m hoping that maybe the damage they do won’t be too detrimental.
    I obviously missed the opportunity to buy the clay from you at the Spring into Gardening Festival last year and won’t be in the country for the next. Very annoying, I would have loved to come, but hey, some of us have to holiday in Thailand!!
    I’ve googled calcined kaolin clay to find stockists. It seems there are stockists in US but not sure about import regulations. Any advice on finding Melbourne stockists?
    Many thanks

    • Leaf, Root & Fruit Post author

      Hi Pat,

      Thanks for sharing your experience with us all.

      As it gets closer to being needed we will be making small sachets of Kaolin available for purchase at our community nights on the first Thursday of the month. See our events page for more details on these.

      Good Luck & Happy Gardening!

  • Jennifer Crockett

    For those interested in buying small amounts of Kaolin, Vasilis Garden sell what they call Citrus Gall Wasp Spray 600g for $49. {maybe a money making opportunity for Duncan to set up in competition with VG!) They didn’t say what was in it so I asked and it is just the clay. I did buy some when they had a special deal going at a reduced price and free postage.
    I plan to use it this spring on my trees. If it is successful I will buy in bulk next time. I emailed AgNova to find out where to buy it and they said ” You can buy Surround at Landmark in Wandin North, Elders Limited in Pakenham, Hoogies in Yarra Glen or at any EE Muir & Sons outlets around Melbourne ” pack size is 12.5kg
    Contact them on info@agnova.com.au if you need advice for where to buy in your area.

    • Leaf, Root & Fruit Post author

      Hi Jennifer,

      Thanks for sharing that info.

      As it gets closer to being needed we will be making small sachets of Kaolin available for purchase at our community nights on the first Thursday of the month. See our events page for more details on these.

      Good Luck & Happy Gardening!


  • Nicole

    Hi I was wondering whether you can just use pure Australian Kaolin Clay (non calcined), known as Eckalite or Eckaglass. You can buy it in bulk from pottery supply stores in Melbourne at a much cheaper price. Checked some US websites they say can use as a truly organic alternative to Surround. Apparently has been used as an organic pest control for many years. Also effective on leafy green crops and tomatoes (so the websites say, I haven’t tried it personally).

    • Leaf, Root & Fruit Post author

      Hi Nicole,

      I have no experience with that product, but it will be great if it works well without harming the tree. Please let us know how you get on with it.

      Good Luck & Happy Gardening!


  • Megan

    Thanks for the update Duncan!
    I have an infested Kaffir Lime that I pruned last year, however, having read your experiment, I think I might try the kaolin clay. Two questions;
    1. As we use the leaves in cooking, is it enough to wash the leaves before using, or would we not be able to use the leaves with this treatment?
    2. Should I prune before applying or leave the galls intact?
    Thanks for your help

    • Leaf, Root & Fruit Post author

      Hi Megan,

      The surround (R) product is used in the horticulture industry to prevent sunburn of fruit. Thoroughly washing the leaves with water should remove all of the residue.

      We are not bothering to prune the galls at all. We simply apply the Kaolin in mid-November, the start of December and mid-December.

      Good Luck and Happy Gardening!

    • Leaf, Root & Fruit Post author

      Hi Kate,

      The Kaolin clay that we use is very fine and readily suspends in water. Most sprayers that you buy at the local hardware store would be fine.

      Good Luck & Happy Gardening!