Citrus gall wasp is a pest that affects all citrus species. Citrus tree owners are encouraged to implement control measures on their property to reduce the threat to the citrus industry in Western Australia and continue to enjoy home-grown citrus fruit.
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.
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.
Visit www.agric.wa.gov.au for more information.