Bridal creeper - squeezing the juice out of the citrus industry
Raelene M. Kwong, Victorian Department of Primary Industries and CRC for Australian Weed Management, PO Box 48, Frankston, Vic 3199, Australia.
Bridal creeper, Asparagus asparagoides (L.) Druce, is largely regarded as an environmental weed, but to citrus growers, it is one of the worst weeds they have ever faced.
Citrus is an important horticultural industry and export earner for Australia. In 2000-01, the estimated gross value of production was $426 million, with exports valued at around $191 million. A total of 83% of Australia's citrus production occurs in southern Australia, mainly in the Riverland, Riverina and Sunraysia irrigation regions of South Australia, New South Wales and Victoria. Alarmingly, this entire region is under threat from bridal creeper invasion, which could pose a significant concern to Australia's citrus industry.
Bridal creeper has been rapidly invading citrus orchards causing a decline in tree health and fruit quality, interfering with harvesting and tree maintenance operations and increasing production costs. The continual invasion of the weed from infested shelterbelts, roadsides and bushland inflicts ongoing financial pressure on growers, which is estimated to cost growers an extra $2000 per hectare per year.
Following the initiation of a biological control program against bridal creeper in the late 1990s, growers were keen to use bridal creeper leafhoppers Zygina sp. and rust Puccinia myrsiphylli (Thuem.) Wint. within their orchards. Consequently, a pilot project funded by the Murray Valley Citrus Marketing Board and the Victorian Department of Primary Industries commenced in 2000 to determine if the biological control agents could persist within an intensively managed system.
The project demonstrated that the agents could establish within orchards and reach very damaging populations within a few years of release. A grower survey also revealed that pesticides and fungicides were not used as frequently as initially thought, and when they are used, they are mostly applied outside the periods of activity of the leafhopper and rust.
More recently, 'spore water' (a suspension of bridal creeper rust in water - see Overton and Overton, 2006) has been applied to citrus orchards using orchard sprayers, and an aerial application by plane has been trialled to achieve broader-scale delivery of the rust. Research into improving the spore water technique is still in progress.
More information about the biological control of bridal creeper in citrus orchards project can be found in Kwong and Clift (2004).
Plant Protection Quarterly (2006) 21 (2) 79.