Citrus gall wasp
Citrus gall wasp (Bruchophagus fellis) is a destructive pest threatening the citrus industry in South Australia.
They are not a declared pest under the Plant Health Act 2009, so you do not need to report their presence and Biosecurity SA will not be applying any specific measures of control.
Background
Citrus gall wasps (CGW) are native to eastern Australia and were first reported in SA in 2010. They are now widespread across the Adelaide metropolitan area.
CGW have a limited flying range, so infestations occur from close proximity of affected citrus trees. It spreads through orchards and across backyard fences of urban properties, usually following:
- introduction of infested citrus plants
- lack of monitoring for gall development in branches.
This pest spreads across long distances by wind and movement of infested trees, or by untreated infested branches.
Impacts
While its natural host is the Australian finger lime, the CGW has adapted to other varieties such as lemons and grapefruit.
The wasp feeding causes stem thickenings (galls) that can weaken trees and make them unproductive. Heavy infestations of CGW can reduce crop yield and cause branch dieback.
Management
Management
An integrated control approach is important for long-lasting results. Follow these steps if you own citrus trees:
- Monitor all citrus trees on your property for galls that signal CGW infestation.
- Target the different stages of the wasp lifecycle.
- Involve neighbours in an area-wide management regime.
Cultural practices
Prune out branches affected by galls – this is essential controlling this pest. Remove as many galls as possible at least one month prior to expected wasp emergence in spring.
Avoid pruning out the galls in winter, which causes the tree to grow vigorously in spring with a flush of new foliage. Yearly pruning regimes such as this perpetuates the wasp lifecycle.
Avoid heavily fertilising trees in winter or spring. Overfertilising, particularly heavy nitrogen applications, can promote excessive spring growth that the gall wasp prefers.
Avoid disposing of affected branches without treatment. Wasps can emerge from galls in off-cuts that are pruned too close to the normal emergence period. Discarded branches should be destroyed or treated so the larva or pre-emerging adults cannot develop. The method will depend on the amount and resources available. Consider:
- mulching
- burning
- freezing (24 hours)
- deep burying (at least >0.5 meters)
- tightly sealing in a plastic bag to be placed in a general waste bin.
Do not dispose of pruned gall off-cuts in normal household waste, green verge collection, or garden bags as it does not eliminate the pest – this spreads the wasp to other areas.
Chemical control
Contact your local nursery or garden centre for the appropriate chemical treatments.
Identification
Adult CGW are dark brown or black in colour and are less than 3mm in size.
Galls in newly infested branches are small and difficult to spot. Check for light-green coloured shoots coming out at right angles from branches during spring to early autumn.
Lifecycle
The CGW lifecycle spans one calendar year. The adult wasp emerges from its woody gall in late spring or early summer, when it is warm enough. Most emerge around the same time, within 20 days of each other. The wasp has only 5 to 7 days to mate and then lay up to 100 eggs under the green bark of a citrus tree.
The eggs hatch after 2 to 3 weeks and feed within the stem for the next 9 to 10 months, causing the tree to promote woody growth around the infected area. These galls become visible from December and gradually enlarge through autumn and winter.
After a short pupation period in spring, the adults emerge from little holes in the galls and the cycle continues.
