Gall wasp is something that nearly every lemon grower in the country has to deal with. In fact, very few trees are exempt. It is a microscopic native wasp that burrows its eggs into the limbs of citrus -primarily lemons and also grapefruit - which then cause swellings or ‘galls’ on the plant, from which the insect hatches.
It’s easy to tell if the wasp has emerged because you will see tiny holes – like a prick from a needle – signifying their departure. Galls without holes means the culprits are still hiding out in the limbs of your plant.
Although gall wasp will not completely kill a tree, it will greatly reduce its health, and more importantly, productivity, when left to spiral out of control.
The best way to prevent gall wasps - along with a host of other citrus issues - is to ensure that your citrus is in good general health. That includes seasonal feeding, mulching and staking; this is particularly important if you have a young plant. Find out How to Care for Citrus here.
Such is the migratory nature of gall wasps that unless we all pruned and rid our trees of every single wasp at exactly the same time, they will inevitably strike back. But measures to reduce infestation include hanging sticky yellow traps and avoiding over-fertilising our plants in early spring, as the young delicate stem growth is the ideal breeding ground for its eggs.
We've also found an organic gall wasp powder to be quite helpful when applied during their hatching season (September - January)
Rather than prune out a swelling every time one surfaces, conduct a controlled prune seasonally to help limit infestation. There is never really the perfect time to prune - there will always be something happening whether fruit or flowers - but we find spring (post winter harvest) to be the best time; for both tree recovery and mitigating fruit loss.
Discard the affected limbs, making sure not to put unhatched galls in the compost. If you can't see pin head sized exit holes on the gall, there are still unhatched eggs inside it. Best to dispose in the bin or burn these limbs
Nearly impossible; the only way to eradicate gall wasp from your life would be to eradicate lemon trees from your life. Regular management is the only measure and it is another pest we have learned to live with.