Citrus gall wasp (Bruchophagus fellis) is an Australian native insect from northern NSW and Queensland and now established in some Perth suburbs.
The spread of citrus gall wasp into orchards and backyard citrus trees is usually the result of the introduction of infested citrus plants and the lack of monitoring of gall development in branches.
Citrus gall wasps have a limited flying range meaning that infestations within a property occur by the close presence of infested citrus trees, including across the fence of urban properties. Spread over long distances is facilitated by the wind and by movement of infested trees or by untreated infested branches.
What to look for
- Prune out branches affected by galls. This is essential for controlling the gall wasp. Prune and remove as many galls as possible by June 30 each year. When pruning newly formed galls in April to June, dry them in the sun afterwards to kill the larvae before disposing of them in your green waste, compost or general rubbish.
- Treat affected branches before disposal. Wasps can emerge from galls in pruning offcuts if pruned too close to the usual emergence period.
- Galls removed after June should be shredded and solarised, or burnt and deep buried. Solarise galls by placing them in a well-sealed plastic bag, preferably by double bagging, and sitting the bag in the sun to bake for at least four weeks. Disposing of gall offcuts in normal household waste, a green verge collection or in garden bags will spread the pest to other areas
- Avoid heavily fertilising trees in winter or spring. Over-fertilising (particularly heavy nitrogen applications) can promote excessive amounts of spring growth that the gall wasp prefers.
Timing of control actions varies with locations. Follow citrus tree development suited to your region.
Chemical control in the home garden is problematic. Chemicals registered for gall wasp are only available in commercial quantities for use in commercial-sized orchards.
Always check the APVMA website and follow label instructions, witholding periods and permit conditions.
Confidor® Guard (Imidacloprid) and Samurai® (Clothiandin) are systemic soil-applied insecticides registered for the control of citrus gall wasp in commercial orchards. They are applied after flowering and control developing larvae before they form destructive galls.
Although petroleum spray oils are used against other citrus insect pests, citrus growers can use them to deter gall wasp adults from laying eggs.
NSW trials with calcined kaolin clay (Surround®) show promise to disrupt egg laying and reducing galls. Apply at least twice during spring when wasps emerge.
For home gardeners, horticultural glue (a sticky non-drying glue made from natural gum resins, vegetable oil and wax) can be pasted over galls in early September to trap emerging wasps, preventing reinfestation.
Megastigmus brevivalvus and M. trisulcus are two beneficial wasps present in WA. They lay their eggs directly into citrus gall wasp eggs, eventually killing the larvae.
Report citrus gall wasp
Use the MyPestGuide reporter app or web tool to report citrus gall wasp so we can keep track of its spread.