Have you noticed strange lumps on the branches of your citrus trees? It could be citrus gall wasp. This pest is found all over Australia and may be the cause of those unsightly lumps and bumps on your lemons, limes, oranges and other citrus trees. We’ll look at why you should treat this citrus pest and the easiest way to do it.
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What are citrus gall wasps?
Citrus gall wasp are tiny black wasps – about 2-3mm long. Found in Australia, they are native to Queensland and New South Wales, but have spread to all parts of mainland Australia.
Adult wasps lay eggs on the new growth of citrus trees, where the eggs hatch and burrow into to the branch. The affected area becomes thickened and hard and develops the lumpy ‘gall’ that the wasps are named for. Citrus gall wasps affect all different types of citrus – lemons, limes, oranges, grapefruits, and even native citrus like finger limes.
Wasps are a problem not just for commercial growers, but for those of us who like to grow our own citrus at home too. I have a lot of citrus trees, and at first only found citrus gall wasp on one of my limes. Unfortunately it has now spread to several of my trees and I am trying to get rid of it once and for all.
Why you should treat citrus gall wasp
Citrus gall wasp lavae survive off the flesh of citrus trees. It’s thought that they can weaken ad affect the overall health of the citrus tree and potentially reduce the amount of fruit produced.
The other reason to treat citrus gall wasp is because the lumpy galls can look very unsightly, Especially if you have ornamental citrus. or dwarf citrus in pots, like I do. No one wants their pretty potted citrus covered in lumps and bumps.
When to treat
To know when to treat citrus gall wasp, you need to know a little about it’s life cycle. Adult wasps lay eggs in the bark of citrus trees. When the eggs hatch, the lavae burrow into the flesh of the branch. To start with there will only be a small thickening of the branch, but as the lavae mature you will see a large bump (or ‘gall’) on the branch. It may change from green to a brown or grey colour.
Once the lavae mature into wasps spring and summer, they leave the gall . You can tell when the wasps have left as the woody galls will have very small holes where the new wasps have escaped. If you see these tiny holes, it’s too late to stop the wasps this year.
The time when wasps emerge can vary depending where you live in Australia. In Queensland and New South Wales, wasps emerge in early spring (September to early November). Further south, it can happen later (October to December).
The wasps will start to lay new eggs as soon as they come out of their galls. So it’s very important to check your citrus trees for galls in late winter and early spring so that you can treat them in time.
Different treatments for citrus gall wasp
Commercial growers use insecticides to treat citrus gall wasps. This makes sense when you consider how many trees they need to treat at once. For those of us who grow citrus at home, there are some other options.
Citrus gall wasp sprays
I am not a fan of using chemicals on my fruit producing trees unless absolutely necessary, so I don’t use citrus gall wasp sprays. There are also some products available which you can paint on the galls to interrupt the breeding cycle.
A popular method of getting rid of citrus gall wasp is to physically remove all of the galls before the wasps emerge. Pruning off affected branches below the gall is effective. If you decide to do this, make sure that you place the removed galls in the bin, or wrap them in a bag and place in the sun for a couple of weeks to make sure any wasp lavae are dead before you put them in the compost.
I use to follow this advice to prune back my citrus trees and remove the galls altogether. This wasn’t a great solution for two reasons. My orange and lime trees ended up being quite harshly pruned for a start. Secondly, this encouraged lots of new growth, which is exactly where the galls wasps like to lay their eggs. In other words, I ended up with even more galls the following year.
Sticky insect traps
You might think that sticky insect traps would be a good alternative, but these aren’t a good option for citrus gall wasps. Sticky traps usually don’t have the right pheromones to attract citrus gall wasps and you’ll just end up trapping good insects instead. So I don’t recommend buying these traps, which are commonly sold at major hardware stores.
The easy way to treat citrus gall wasp
Thanks to Gardening Australia, I learnt a much better way to treat citrus gall wasp. It doesn’t involve harsh pruning. And it doesn’t involve any chemical sprays, which is perfect for organic gardening. It’s a cheap option too. You’ll only need a simple vegetable peeler!
Inspect all of your citrus trees for signs of citrus gall wasp in late winter and early spring. Wasps love to lay their eggs in the new green growth. Where you see a thickened gall developing, use a vegetable peeler to remove the thickest part. Only peel one side of the gall lump. as you don’t want to ring bark the branch. Peel layers gradually until you can see where the lavae are developing. You’ll see the cells as round spots in the flesh. Once exposed, the lavae will die and won’t grow into adult wasps. It’s as simple as that!
On the left above you can see where I have started shaving the galls on my potted lime – this needed a few more goes to expose all of the lavae. On the right are some galls on my mandarin orange, which is in another pot very close to my lime.
Tip: buy yourself a new vegetable peeler for cooking and use your old one to remove your citrus galls – it’s a good way to remember to replace your peeler with a nice shiny new one!
Get your neighbours involved
While citrus gall wasps can’t travel very far, your chances of eradicating them will be even better if you can get your neighbours with citrus to treat their trees too. Make sure to tell them about the vegetable peeler trick so they know how easy it is. Or offer to help them find and shave any galls on their lemon trees and other citrus. If you all work together, you might be able to achieve a gall wasp free zone in your neighbourhood.
Other citrus tree problems
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