Gall Wasp Traps Don’t Work. Try This Simple Method Instead.

Anyone who has grown Citrus Trees in Australia will likely be familiar with the dreaded gall wasp, and the unsightly tree galls that they leave in their wake every Spring and Summer. 

These native insects have developed a reputation for being very hard to get rid of. The huge galls that they leave behind are often ugly and misshapen, and they have the potential to cause damage to your beloved citrus tree in the long run. 

What’s even worse is that the Gall Wasp traps sold in gardening and hardware stores are not particularly effective at eradicating these pests. Thankfully, there is one simple method you can use instead that gets you fast, easy results without much fuss. 

Read on to find out more about where Gall Wasps come from, how to easily remove an infestation from your tree, and how to prevent the pesky things from moving in to begin with. 

Gall Wasps Are A Widespread Problem In Australia

Gall Wasps (or Bruchophagus Fellis) originated in northern Australia, where the insects were naturally hosted by native Finger Limes and other local citrus varieties.

After citrus trees like lemons, oranges and grapefruit were introduced to the country, the Gall Wasp slowly spread south to New South Wales, Victoria, South Australia and even Western Australia. Now they are a widespread problem – particularly around suburban Melbourne, where citrus trees are highly popular in the warmer months.

At around 2-3mm in length, these tiny black wasps incubate their young inside the branches of your citrus trees during Spring and Summer. The tree will detect the growing wasp larvae as foreign bodies and try to reject them, causing the branch to break out in lumps called galls. This stresses your tree out, leading to weak branch growth and poorer fruit yields.

When the wasps hatch, they’ll drill themselves out of the gall and leave it pockmarked with tiny little holes everywhere. The shiny little nuisances then go on to breed and lay more eggs near where they’ve just hatched, spreading the infestation further throughout your citrus tree.

Gall Wasp Traps Are Not Effective.

As the problem has become more widespread, gardening and hardware stores have taken to selling Gall Wasp traps, usually in the form of sticky sheets or cylinders that hang from the tree and function like a traditional fruit fly trap. Unfortunately, they also trap and kill the helpful pollinating insects as well, potentially doing more harm than good to your citrus tree.

In our experience, these traps have proved totally ineffective in actually preventing wasps from moving in. This isn’t a controversial opinion either – many professional gardeners are outspoken in their dislike of Gall Wasp traps and there is little evidence they work at all.

Pruning Gall Branches

Another common method in the past has been to prune and dispose of any gall-afflicted branches before the wasps hatch. This is an effective method if you only have one or two heavily infested branches, but it’s useless if they are all through your tree. Cutting off too many branches is not viable – it leads to less fruit and gradually weakens the tree overall.

This Simple Trick Effectively Kills Gall Wasp Infestations.

Thankfully, gardeners have recently discovered that there is actually a much easier and more effective way to wipe out Gall Wasp infestations in your citrus trees.

We picked this trick up from a very informative ABC Gardening video a few years ago, and it’s called the ‘Peel and Reveal’ method. In our experience, it works like an absolute charm. All it takes is some keen observation skills and a sharp knife – even a potato peeler will do!

When you spot a gall on your citrus tree, use your blade to peel off one side of the active gall. You can also look for the most swollen section of the gall and slice it open right down the middle. This will ‘reveal’ the unhatched larvae and expose them to the outside air, killing the whole batch instantly and effectively.

No need for indiscriminate traps or heavy-handed pruning – it turns out killing Gall Wasps is really as simple as a quick cut. However, you’ll need to make sure you’re onto it right at the beginning of wasp season, usually around late Winter to early Spring. You should also make sure not to accidentally ringbark any of your branches, as that can do serious damage.

Gall Wasp Prevention

While the Peel-and-Reveal method is a great way to deal with galls as they appear, it can be better to try and prevent them from appearing in the first place. Following these tips can help to prevent you from creating the perfect Gall Wasp conditions in your citrus tree:

1. Avoid Pruning or Over-Fertilising in Winter: Pruning your trees heavily in late Winter will lead to soft new growth just as Spring is beginning. The wasps love to burrow into this soft moist wood, and it creates perfect conditions for laying eggs. Overfeeding or over-fertilising at this time can also have similar effects on growth, and the extra moisture and nutrient build-up may only attract insects further.

2. Coat Your Tree in Horticultural Oil: Another method that gardeners use to fend off Gall Wasps is oil. Coating the new growth in your tree with a plant-safe oil product from July through to August is thought to block the female wasps from laying their eggs in the soft wood. White Oil is a popular solution to this problem, and there is some suggestion that Eco-Oil may also help by attracting the Gall Wasp’s natural predators, which are even bigger wasps. Yep, lovely stuff.

3. Warn Thy Neighbor! Citrus trees are everywhere in Melbourne. Growing your own citrus is a tradition for the large Greek and Italian migrant populations, and the climate is absolutely perfect for it here. However, this abundance is also what gives the Gall Wasp such a foothold. If you notice a tree is infested, tell your neighbours to check their trees as well and prevent the wasps from moving straight back in. If you work together, you may manage to remove them from the entire area!

Other Common Citrus Pests To Watch Out For

If you follow these prevention tips and are quick to destroy any galls as they appear, you should be well prepared to defend your precious Citrus Trees over Spring and Summer.

Unfortunately, Gall Wasps are not the only pests you will have to look out for. Here are some quick tips for dealing with the other irritating pests that can affect citrus trees in Australia. You can check out this free, in-depth guide from Citrus Australia for even more detailed info.

Scale Insects

These annoying pests are one of the main pests that citrus trees deal with. Scale will settle on the leaves and fruit, and if left unchecked, it can seriously damage or even kill your tree. The presence of scale can also cause ants to move in and do further damage to fruit.

You can identify scale by the blemishes on fruit and leaves, and it can be easily treated with a White Oil Spray. In mild cases, you can use an alcohol-soaked cotton swab and pick off the insects by hand. In the long term, native plants that attract predator insects can help to prevent scale insect populations from growing out of control.

Mites

These tiny insects are a problem all across Australia, and they can cause settle on the fruit and leaves of your citrus tree. You should check vigilantly for mites from Spring through Autumn when these insects are most active. 

You can usually find them on the underside of the leaf, though you will probably need a magnifying glass to see them at all. A mite is so small that it damages leaves & fruit by biting through the plant cell wall and sucking out the contents – it’s creepy stuff.

To treat a mite infestation, either spray your tree with an extra-strong hose blast or wipe down infested areas of the tree with a soap mixture. Mix 1 tsp of soap with 1L of water, then spray the undersides of the affected leaves with it to make sure all the mites are covered.

Wash off the solution 2-3 hours later, and remove all of the soap residues from the foliage surface to avoid any leaf burn. Repeat this process every 4-7 days until the mites are gone.

Queensland Fruit Fly

Like Gall Wasps, these insects have been a huge problem in northern Australia for a long time. Unfortunately, there is evidence that they have recently spread to Melbourne and are causing headaches for both commercial and home gardeners, particularly between October and May when they are most active.

It pays to be vigilant against fruit flies as they can be quite devastating to your citrus tree. If you remove any affected fruit, be sure to seal it in a plastic bag before disposing of it in order to kill off any potential larvae. Netting your trees can also add extra protection. Agriculture Victoria has recently posted a useful & comprehensive guide for how to deal with these fruit flies in your home garden. 

---

Citrus trees are one of our favourite plants to grow, and a lot of love and care goes into them over the years. It can be stressful or even devastating to see your beloved tree affected by pests, which is why it’s so important to know how to get rid of them quickly and effectively!

Hopefully, this guide has given you the confidence to deal with infestations of Gall Wasps or other common citrus pests if they happen to occur in your garden. If you’re having trouble with a specific pest, or you have any garden questions at all, you can ask one of our friendly gardening experts for advice. They’ll be more than happy to help you figure it out.