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
Pruning is essential for controlling citrus gall wasp.
- Prune out galls before June 30 to avoid the need to treat before disposal. Larvae inside the galls will not survive and gall wasp will not be spread. This is essential for controlling the gall wasp. Pruned material can be kept at the property or go into green waste (bin or verge collection) or general rubbish.
- Galls removed after June should be treated before disposal. Wasps can emerge from galls in pruning offcuts if pruned too close to the usual emergence period, spreading the pest further around the State. Treat galls by either:
- Solarising by placing them in a well-sealed plastic bag and left in the sun for at least four weeks. For bulk cuttings, galls can be securely covered with a tarp.
- Shredding/mulching - if it is close to emergence (spring) make sure galls dry out or solarise this material.
- Burning (if permitted) - check your local government guidelines and total fire bans.
- Alternative options:
- Burial or heating – likely impractical and these options have not been researched, but wasps aren’t expected to be able to emerge from galls, if buried >30cm. Wasps won’t survive in galls that are heated to a temperature too hot to hold.
- Soaking in water - likely impractical and this option has not been researched. Consider solarising via bags or tarps to contain the wasps and encourage desiccation.
- 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.
- Work with your neighbours. For Perth gardeners, working with citrus tree owners in your area will have the most success.
- Check new trees before purchasing or moving and re-check in June. The spring-summer period can be a particularly risky time for spreading the pest unknowingly as the galls on an infested tree may not be visible.
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. Unfortunately, they are not present in sufficient numbers to control citrus gall wasp.
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. Make sure you include a photo of the galls and your location (suburb) when making your report as this is important information for us to confirm the pest and track its spread.