Citrus gall wasp (Bruchophagus fellis) is an Australian native insect from northern NSW and Queensland and now established in some Perth suburbs.
Preventing the spread of citrus gall wasp will help commercial and home citrus growers. The local citrus industry will be able to keep production costs down and home owners will be able to enjoy the fruit they have cared for.
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
The wasp produces characteristic woody galls which form around the developing larvae. Monitor for its presence between June and September (winter-early spring).
Search for forming and already formed galls on young, green twigs which contain the larva developing into mature pests.
Galls located further up the branch or on older branches can indicate that there have been older infestations (previous year or earlier). The presence of holes within the gall indicates that adults have already emerged.
Inspect for the presence of galls in all nursery stock and new plants prior to, and after planting for at least 12 months.
Check for galls on established trees all year round.
Prune out branches affected by galls. This is essential for controlling the gall wasp. Prune and remove as many galls as possible at least one month prior to expected wasp emergence in spring.
Avoid pruning out the galls in winter. This causes the tree to grow vigorously in spring and resulting in a flush of new foliage that the gall wasp prefers. Yearly pruning regimes such as this perpetuates the gall wasp cycle.
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.
Avoid disposing of affected branches without treatment. Wasps can emerge from galls in pruning off-cuts if pruned too close to the normal emergence period. Discarded branches should be mulched, burned or deep buried (1m). People growing citrus trees need to understand that disposing of pruned gall off-cuts in normal household waste, green verge collection or in garden bags does not eliminate the pest – it spreads the pest to other areas.
The wasps Megastigmus brevivalvus and M. trisulcus insert their eggs directly into the egg where it slowly develops in the host larva, eventually killing it.
DPIRD has released these parasitic wasps in 2015 to determine its potential estabishment as a biocontrol agent in Western Australia.
- Methidathion (Suprathion®, Aako Ridacide®) is an insecticide registered for the control of citrus gall wasp in commercial orchards. Applied four weeks after gall wasp emergence is completed, this non-systemic pesticide kills adults on contact.
- Clothiandin (Samurai®) is a systemic soil-applied insecticide used to control Mediterranean fruit fly which can significantly reduce galling.
- Although petroleum spray oils and Confidor® Guard are used against other citrus insect pests, citrus growers can use these insecticides 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.
NOTE: Pesticides are extremely disruptive to integrated pest management and organic food production.
Timing of control actions varies with locations. Follow citrus tree development suited to your region.
Report citrus gall wasp and other citrus pests
Use MyPestGuide reporter app or web tool — go to mypestguide.agric.wa.gov.au or call the Pest and Disease Information Service on (08) 93683080.