Citrus tree owners called to stop the spread of citrus gall wasp
The Western Australian citrus industry is concerned about the spread of citrus gall wasp throughout the main growing regions of Western Australia.
Citrus gall wasp (Bruchophagus fellis) is a native Australian wasp whose original host was the Australian native finger lime found in northern New South Wales and Queensland.
Over time it has spread throughout the major citrus production regions of eastern Australia where it has become a major pest of citrus trees.
The pest was discovered in the Perth suburb of Eden Hill in 2013 and subsequently in a number of surrounding suburbs.
The spread of citrus gall wasp is usually the result of the introduction of infested citrus plants and the lack of monitoring of gall development in branches.
While these wasps have a limited flying range, infestations within a property occurs by proximity to infested citrus trees.
Spread over long distances is facilitated by the wind and through the movement of infested trees or by untreated infested branches.
Females lay around 100 eggs under the bark of new season flush growth in the first few days after their emergence.
The egg, larval, and pupal stages occur within the galls on branches which become larger and more obvious as time progresses.
Adult citrus gall wasps emerge from galls on citrus limbs in spring each year with most adults active in late September to mid-October.
The galls interfere with nutrient flow in the new shoots and affect fruit setting.
Uncontrolled, it can result in reduced fruit size, tree vigour and yield with extreme infestations causing branch dieback and potential tree death.
The prevention of its spread to commercial citrus growing areas will greatly assist local industry in keeping production costs down.
Control methods
Although chemicals exist to control this pest they are expensive and can be disruptive to integrated pest management systems.
The best control method is the disruption of wasp emergence.
The following tips will also help reduce infestations:
- 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 results 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.
An information campaign is currently underway to inform citrus tree growers about the steps they can take to control and stop the spread of the pest. Visit agric.wa.gov.au/citrusgallwasp
Commercial citrus growers also need to monitor their orchards for signs of citrus gall wasp and take appropriate steps to control it if required.
Early detection and control will greatly assist in reducing the damage caused and keeping pest numbers low.
The campaign is a joint action of the Department of Primary Industries and Regional Development and WACitrus.
Report citrus gall wasp and other citrus pests by using MyPestGuide Reporter.
Alternatively call the Pest and Disease Information Service on +61 (0)8 93683080.
For more information contact Kevin Lacey, Technical Officer, South Perth, +61(0)8 9368 3546.